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Reader Chemistry TTO-3

Chapter 1. Atoms, molecules and properties of matter

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Contents

o 1.1 What is chemistry?

o 1.2 Performing research in natural sciences.

o 1.3 Safety rules.

o 1.4 Writing a report.

o 1.5 Properties of matter, pure substances and mixtures.

o 1.6 Building blocks of substances, kinds of atoms and elements.

o 1.7 Different types of substances.

o 1.8 Molecules, atoms and properties of matter.

o 1.9 Pure substance or mixture?

o 1.10 Separation of mixtures: making use of the differences in properties of matter.

o 1.11 Concluding: test-yourself.

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1.1 What is chemistry?

During the first and second grade you had a topic called Science which is an introduction to the

natural sciences biology, physics and chemistry. You learned to study the phenomena around you,

to understand them and sometimes even to explain them. In the third grade you will study these

subjects separately. But do you remember the differences between biology, physics and

chemistry?

1. Biology is the natural science studying living organisms. How do these

organisms behave, what is their interaction with each other and their

environment, their anatomy, what are their similarities and their

differences? Biology studies all aspects of life. It consists of many

subtopics, for instance:

o Ecology: the interaction between between living organisms

o Ethology: animal behaviour

o Paleontology: the knowledge of fossils

o Anatomy: the study of the different structures and the organisation of these different

structures within a living organism.

2. Physics is the natural science studying the general features of materials. It tries to

understand why these materials behave the way they do and to predict this behaviour.

Some well known subtopics are:

o Electricity

o Velocity

o Energy

o Forces

o Light

o Sound

3. Chemistry is the natural science studying the properties of

substances by looking at the way they are structured. With

chemistry you will study how the properties of a compound will

change when you change its chemical structure.

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So physics and chemistry both look into the properties of substances. But there is a clear

difference between them if you look at the change in properties:

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• A physical change is an action that can be restored to the original state. This is called

‘reversible’. Examples of such changes are: a block has moved up to a higher altitude, the

temperature of an iron bar has been increased, the velocity of a cyclist has been

diminished. All of these are physical changes. The block can be lowered, the temperature

of the iron bar can be brought down and the cyclist can speed up to its original velocity, as if

nothing happened. All changes are restored to the original situation, they are reversible

processes.

• A chemical change cannot so easily be restored to its original state, these changes are

irreversible. These changes bring about something definite to the the material. Example

given the burning of a piece of paper or the boiling of an egg. Both processes changed the

structure of the original material: the piece of paper and the egg. The piece of paper now is

a small heap of ashes and the egg has become white and solid. If you regret the burning of

this piece of paper, sorry, you cannot undo the process. The chemical structure of the

paper has completely changed, in an irreversible way.

In Science you’ve been taught that all three natural sciences play an important role in our daily

life. An example is pharmacochemistry, the science concerning the way medicins act on living

organisms. Knowledge of Biology shows us how a disease influences the organism, the effect

of this disease on the organism and how to handle the disease medically. Chemistry tries to

find the chemical structure of a medicine to cure the disease, to kill the pathogen or to

decrease the pain. Physics tries to find ways to administer the drug to patients, by using

systems (pumps) installed within the body. The system has to be very precise, so exactly the

right amount of medicine is released by the system within the body every hour.

Natural scientists perform experiments. These experiments always have a purpose, you perform

an experiment to find an answer to the question concerning the

experiment the goal of this experiment, your research question.

Quite often you expect certain results from this experiment,

your hypothesis. Doing experiments you can proof your

hypothesis is right or wrong. The coming year you will perform

experiments during your chemical class regularly and often

your purpose will be to proof that the results of your

experiments are in agreement with the Theory. Or, in other

words: you will proof this reader is right!

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1.2 Performing research in natural sciences

By doing experiments -by doing research- humanity is enlarging her knowledge. The possibilities

are increased and our views enlarged. Diseases are overcome, new technologies further

developed and put into practise and humanity is exploring space. Large discoveries always come

from small discoveries, from small experimental research.

Scientific research always follows a fixed number of steps (see figure 1):

• What is the problem? The research question

• What do you think is the answer to this question? The hypothesis

• You design an experiment to answer this question

• You plan exactly how to do the experiment

• You do the experiment

• You write down, very precisely, your results and other observations

• You check if the experiment is in agreement with the hypothesis or not: true or false.

• New questions lead to new experiments.

The progress of an experiment:

• An action: you do something, you execute an action;

• An observation: by executing an action something will change, you can observe this

change; in this step you need to use your senses;

• The conclusion: you think about your observations, your results, and draw your conclusion;

in this step you need your brain, you think about your observations.

Logbook:

• When you perform an experiment you keep a logbook. Very precisely you write down your

actions and your observations. A number of experiments are inserted in the reader and

there is always some blank space to to use as logbook. Important for the writing of a report,

but also for studying to a test!

Questions.

1) Explain how a research cycle works. 2) Describe the difference between an observation and a conclusion. 3) Explain why writing a logbook is important for an inventor.

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4) Decide if the following sentences are describing an action, an observation or a conclusion: a. Rianne writes a sentence in her logbook. b. She writes with blue ink. c. Jenno ignites the burner. d. He lights a piece of paper with the burner. e. The paper becomes black. f. Paper is flammable. g. During the combustion heat is released. h. It is a complete combustion. i. Less mass of ash is formed than the mass of paper combusted. j. During combustion, gasses are released.

5) “Large discoveries always come from small discoveries, from small experimental research”. Explain this statement by looking at the invention of a mobile phone.

Figure 1. Research cycle

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1.3 Safety rules

In daily life you have to follow all kinds of rules. And there is a reason for that, imagine football

without rules! When playing important football matches six (!) referees are needed to see if the

rules are followed well and even then something might go wrong. Therefore camera’s are installed

to solve misunderstandings and to create a fair match. Or: imagine how many students would

arrive at school alive without the traffic rules! So, now you understand why we have these rules:

life is a lot safer and we all know how to behave ourselves, in playing football, participating in

traffic and in life in general.

While doing an experiment in class, you also have to stick to the rules. These rules exist for your

own and other people’s safety and to make things clear for everyone. In chemistry we often work

with Bunsen burners and if something goes wrong serious burns may occur! Keep in mind that all

substances are real and toxic. You do experiments to practise your skills and link the real world to

Theory. As you know by now, we perform an experiment to answer a research question. This

means you read all instructions very well first:

o you have to know what is expected from you; which research question(s) are you

suppose to answer and how exactly are you going to perform the experiment?

o which dangers are involved in doing the experiment?

o what is needed?

o if you do an experiment work as a group: who is going to do what?

o what is your hypothesis?

o after all these preparations, and not before that, you can start with getting the things

for the experiment.

During chemistry experiments the safety rules have to be followed:

1. Each chemical substance might be poisonous / hazardous: never taste a substance

2. Eating and drinking in the laboratory is not allowed

3. Make sure you never get in touch with chemical substances

4. Never smell a chemical substance directly but bring the smell carefully (waft) to your nose

5. Protect your skin and clothes by wearing a lab(oratory)-coat during the experiment and

make sure it is buttoned up

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6. Always wear safety goggles if you

a. heat substances

b. work with hazardous substances

7. Long hair is tied up (pony tail); this is

absolutely necessary doing experiments with

the Bunsen burner

8. Make sure your working space is as empty as

possible and only have the the necessary

things there

9. Concentrate on the experiment and don’t do other distracting things

10. Stick to the instructions; it is highly forbidden to add some substances together by yourself

11. Never point the opening of a test tube at yourself or anybody else

12. Clean your working space thoroughly after finishing the experiment

13. Put everything you have used back to its proper place

14. Wash your hands well after the experiment and the cleaning up

15. When in doubt: ask your TOA or the teacher.

Figure 2. Safetylabels for chemicals.

Some of the substances you work with need special precautions, indicated on the label on the

container. This label shows a pictogram and these pictograms demonstrate a special hazard

working with that particular substance. The pictograms have been renewed beginning of 2015.

Figure 2 represents both sets of pictograms and for the test you have to learn both sets.

Experiment 1

Irritation Poisonous Flammable Corrosive Environment Explosive Radioactive

Old

New

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Questions.

6) Which substance is on the outside of the test tube after heating it with the yellow flame?

7) Which flame are you going to use heating a test tube filled with water? 8) Which flame are you going to use for heating a container with one litre of water? 9) Which flame is hottest: the yellow, the blue or the roaring blue flame? 10) You just carried out the experiment with the Bunsen burner.

a. Which safety rules did you apply? b. Which safety rule do you consider most important? And which one less

important? Explain your answer well! c. Why are all safety rules important according to your teacher?

11) Why does a candle burn with a yellow flame?

1.4 Writing a report.

It is very important to write down all your measurements and observations during the time you

perform an experiment. This allows you to write a proper and accurate report of the experiment

later on. In the report you give your results, your measurements/observations and the conclusions.

Sections of a report:

The following notes demonstrate the contents of a report. For a proper report you simply follow

these notes. Not always all notes are have to be included. Therefore you have to ask your teacher

which notes have to be included in the report and which ones can be left out. Often students ask

how many pages the report should be. This is hard to say upfront. A report must be as elaborate

as needed for your team to show the teacher that you have done a good experiment and that you

completely understand it.

1. Title (only a couple of words):

The title of the experiment. Quite often this title is included in the instructions of the experiment. If

not, try to summarise the experiment. Most of the time, the title is on the front page together with

the names of the authors and the date.

2. Introduction (1 paragraph):

A short introduction to the experiment. You summarise the purpose of the experiment, why you did

the experiment and how you performed the experiment. The purpose of the introduction is to raise

the curiosity of the reader. Often, topics 3-6 are combined in the introduction.

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3.Inclusive theory (1 paragraph or 1 A4, depending on the level of complexity of the experiment)

Explain the principles of the experiment. What does the reader has to know to be capable of

understanding the experiment? Try to keep this part concise. Formulae and reaction equations

have to be included. If you use abbreviations in the formulae, explain their meaning in a table.

4. Research question (1 sentence)

You simply state the purpose of the experiment. What are you going to research?

5. Purpose of the experiment (1 paragraph)

State concisely the purpose of the experiment, but also which kind of research you are going to

perform. Is it mainly practical research? Or is your research descriptive? This is important for the

results and conclusions in your report.

6. Hypothesis (1 paragraph)

A prediction of the results and conclusion, based on theory. What do you expect to happen and

what do you expect the results and conclusion will be?

7. Materials

A shopping-list of the things needed for the experiment.

8. Method (depending on the experiment)

Describe step by step what you are going to do or what you have done. The reader has to

understand what is happening. It is not necessary to include the logical safety precautions like ‘put

on a labcoat’ or ‘make a ponytail’. Also in this section you draw your apparatus if used.

9. Observations (depending on the experiment)

In this section you write down all observations made. If you made drawings of your observations,

they have to be in this section.

10. Results (depending on the experiment)

All measurements and calculations have to be in this section. If a formula is used, you refer this

formula in this part of the report (normally the formula can be found in the theory).

11. Conclusion (a couple of lines)

The answer to your research question. The conclusion contains intelligence because you draw a

conclusion coming from the results and the observations of your experiment.

12. Discussion

A short discussion about the running of the experiment. Did it all go well or did something go

wrong? Do you think this influenced your results and if so, in what way? This specifically doesn’t

mean that we want to hear about the collaboration or the lack of collaboration in your group. You

have to take a close look at your workings an the outcome of the experiment, are the results

thrustworthy? Also you can indicate how to continue this research. If the results could not be

trusted or were strange in any way, you should suggest a follow-on experiment.

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So far we have repeated the easy stuff of the science classes.

Things you have to know from paragraphs 1-4

• Differences between chemistry, biology and physics

• How research works

• Differences between a conclusion, an observation and an action

• The safety rules

• How a Bunsen burner works

• How to write a report

Questions

12) Explain what the difference is between a reserach question and a hypothesis. 13) Explain what the difference is between a conclusion and a discussion in a report. 14) Joost dissolves a white solid substance in water and this gives a blue fluid. Are the

following statements a conclusion, a discussion, a hypothesis or a research question in the report of this experiment?

Na het oplossen van de witte stof kregen we een helder blauwe oplossing. After the white solid was added to the water, we obtained a blue fluid.

Can a white solid in water give a blue solution? I expect that the solution of a white substance will not turn blue. Sugar

and table salt in water don’t give blue solutions, so why would this one? When the white solid was added to the water, the water became blue.

However, we also saw that a gas was formed and in addition, the fluid became warm. It looks like a chemical reaction happened because a gas and heat were formed.

Dissolving a white substance can give a blue solution. However, this is not true for all white substances.

Assignment 1

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1.5 Properties of matter, pure substances and mixtures.

Molecules

Coke is a tasty, dark liquid which people in the Netherlands drink a lot. Every year about 559

million liters of Coke is sold in this country! And all this for a drink mainly consisting of water.

Mainly, because Coke contains quite a number of other substances in addition to water. The drink

is dark-brown and pure water is not brown. So, Coke contains a substance causing this brown

colour. Water is tasteless and Coke is pretty sweet.

The sweet taste is caused by a huge amount of sugar

in Coke. There also has to be a gas in Coke, because

it bubbles. This gas is called carbondioxide. Coke

contains many more substances and all together they

make the product Coca Cola. So, Coke is a mixture of

quite a number of different substances. And: not all

types of Coke are the same. For instance: some people prefer Coca Cola to Pepsi Cola or vice

versa. Also Coke is sold in many different types, with sugar or without, with vanilla or not, etcetera.

All different types are produced by omitting substances or adding substances to the original recipe

of Coca Cola.

In the past centuries many scientists asked themselves the question how to define ‘a substance’.

They concluded that substances consist of very tiny particles, so small that they are not visible to

the naked eye. Even using a microscope the particles cannot be seen. We call these particles

molecules. All matter consists of molecules.

Molecules are so small that we cannot draw them at their real size. So, to represent molecules we

work with models. In the second grade you’ve been taught to use a simple model, that is to

represent each particle by a little ball. In this model each ball represents the smallest amount of a

substance, a molecule, so each ball represents one molecule.

Figure 3. Pure liquid water A solution of sugar in liquid water

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A pure substance consists of only one type of particle, only one kind of molecules, so in the model

all balls will be of the same colour. A mixture consists out of balls with different colours, so

different types of molecules. This is represented in Figure 3. A red ball represents a water

molecule and a black ball represents a sugar molecule. The first model shows pure water, only red

balls. In the second model, water with sugar, red and black balls can be seen. Water with sugar

consists out of two different types of molecules, water molecules and sugar molecules.

A pure substance consists of one kind of molecules

A mixture consists of two or more kinds of molecules

Representing Coke as a model, you would need quite a number of different coloured balls. By now

you know that Coke is a mixture of quite a number of different substances. Coke doesn’t only

contain water molecules, but also molecules of sugar, molecules of the gas carbondioxide,

molecules of a brown pigment and many more. And all those molecules together make that lovely

tasty drink.

Assignment 2

Questions

15) Explain if the next substances are a pure substance or a mixture.

a) orange juice; b) 7-up; c) wood; d) paracetamol; e) fresh air

16) Name a substance that can be called chemically pure. 17) For which types of substances purity can be really important?

Assignment 3 Assignment 4

Everything around us consists out of substances, matter. A lot of people define a substance as

something you can touch, but that definition is not completely correct. A better definition of a

substance is: a substance is something with mass. This definition is also correct for air, because

air has mass. Each substance also has properties. These properties are caused by its molecules.

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Different substances have different properties of matter. For example at room temperature, air is a

gas but the substance water is a liquid and iron is a solid. Sometimes substances have a number

of properties of matter in common, but differ in other properties. An example will clarify this.

Suppose you find a jar containing a white powder. You may conclude ‘this is table salt’, because it

is a solid white substance, but in doing so you could make a very big and dangerous mistake. You

even may become seriously ill! As you know, there are quite a number of white substances. If the

white powder is icing sugar, it is not that horrible. Maybe your egg doesn’t taste the way you want

it to, but that is not dangerous. But if the white substance turns out to be poisonous, you might die

after eating your egg! So it is very important to describe a substance as well as possible using

specific properties of matter.

All substances consist of molecules. Molecules have mass. A property of matter is a property specific for that substance/molecules.

In chemistry we prefer to use properties of matter specific to a substance, so preferably we use

properties which are not very common. If only a few substances have this specific property, the

chance you have that specific substance with that property is quite big. The less substances with

that specific property, the more you can be certain that the substance is the substance you think it

is. Of course you first have to determine this specific property experimentally and precisely. A

number of properties of matter have already been explained during science class: boiling point,

melting point and density are very specific properties of matter.

Experiment 2

Assignment 5

1. Melting and boiling.

When ice melts it changes from the solid state of matter to the liquid state of matter. This change

of state is caused by heating, by changing the temperature. The temperature at which this change

of state occurs is a specific property of matter. The temperature at which a substance melts is

called the melting point, and the temperature at which a substance boils is called the boiling point.

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Melting point and boiling point are examples of constant of matter. You can find a melting point or

a boiling point in a book of data. It is represented as a number followed by a unit, °C, degrees

Celsius.

A constant of matter is a property of matter which you can express with a number followed by a unit

Ice (solid water) becomes a liquid above 0°C (melting) and even a gas when heated up to 100°C

(boiling). These temperatures are very specific for the substance ‘water’. But what is happening

specifically during the change of state?

Figure 4. Triangle of phases.

You can explain this by looking at the particles separately, as you did in science class (figure 4).

Heating gives a form of energy to the substance, in our case ice. In ice the particles are very close

together. The energy makes the particles move more, and therefore they need more space and

become more extended, so less close and less structured.The ice has melted and is by now

water, a liquid. If the heating is continued, the particles gain even more energy so move even

more. If the water has obtained enough energy, the particles will let go of each other and the water

will evaporate and becomes water vapour, a gas. The more you heat the water, the more particles

will have enough energy to leave the water surface. At 100°C each particle at the water surface

has enough energy to leave that surface: the water boils. Plotted in a graph with temperature

against time, this phenomenon would look like figure 5.

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Figure 5. Temperature-time diagram

We know water boils at 100 oC (the water is changing phase, liquid to gas) and melts at 0oC (the

phase changes from solid to liquid).These are very specific properties of water. If you look at

Table 1 you will find a list with some common substances, their melting points and their boiling

points.

Table 1. Melting and boiling points of some common substances.

substance melting point (°C) boiling point (°C) alcohol -114 78 aluminium 660 2467 carbondioxide -79 -57 copper 1084 2570 iron 1538 2750 glycerol 19 290 gold 1064 2808 lead 327 1751 mercury -39 357 oxygen -219 -183 silver 962 2155 sulphur 113 445 tin 232 2625 water 0 100

At room temperature, alcohol is a colourless liquid, just like water. However, both the melting point

and boiling point are completely different. Below -114oC alcohol is a solid and it already boils at

78oC. So water and alcohol differ in these specific properties of matter, while they share the more

common properties like being a liquid at room temperature and being colourless.

Quesions

18) a) Describe what will happen to the water molecules in heating water of 20°C to 100°C. Just mentioning a phase shift is not enough!

b) Do the water molecules change when the water is boiling?

c) Draw, in a model, the change from liquid water to water in the gas phase.

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19) Explain the blurring of glasses going from outside to inside during winter time. 20) a) Explain the difference between sublimation and evaporation.

b) Name the phase shift going from a gas to a solid.

c) 100g of water is going from the liquid to the gas phase, resulting in a huge increase in volume. Explain this phenomenon.

21) a) Explain what will happen if you transfer a bottle of Coke from the cupboard (22°C) to the refrigerator (4°C). Just saying that the Coke is getting cold is not enough!

b) Someone buys a bottle of Coke to take to the beach. But, this person forgets to take the bottle from the car and leaves it in the hot car for 8 hours. When he wants to go home, he notices the bottle has exploded and the car is quite dirty. Explain why the bottle has exploded.

22) Try to think about what the density of cola will be incomparison to the density of water. Explain your answer.

2. Density

We know substances have mass. And each substance consists of particles being very close

together in a structured way (solid), slightly further apart in an unstructured way (liquid) or very far

from each other, completely without touching (gas). The space between the particles (the volume)

and at which temperature changes in this space will occur (melting point and boiling point) is

specific for each substance. Combining these two factors you can conclude that each phase

holds a specific number of particles within a known volume. And those particles have a mass. This

way you get the term ‘density’ (ρ). Density is defined as the mass of a substance per volume at a

known temperature. For this temperature we normally take room temperature (20oC).

ρ = m/V at T = 20oC

The density of a substance is the mass of that substance per unit of volume

Complicated? Don’t worry, it’s not! Lets look at the following example. Suppose: you have three

bottles, one litre each. So the volume (V) of each bottle equals one litre. And now you fill these

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three bottles with three different substances and with the aid of density you can predict which

bottle will be heaviest. You fill the first bottle with air, the second with pure water and the third one

with solid gold. Your expectation, your hypothesis, probably tells you the bottle with gold will be

heaviest and the bottle with air lightest. You are right. Look at the density of the substances (see

Table 2): for gold: 19.30 g/cm3, for water: 1.00 g/cm3 and for air: 0.00129 g/cm3.

One litre = 1dm3 = 1000 cm3. So you can convert these densities to:

gold: 19.30 kg/L, water: 1,00 kg/L and air: 0,00129 kg/L. So one litre of air, according to the

density of air, contains only 0.00129 kg = 1.29 gram of substance. One litre of gold has a much

higher mass: 19.3 kg! That bottle is heavy!

Table 2. Density of a number of substances.

Substance Density (g/cm3) Solid substances aluminium 2.70 diamond 3.52 glass 2.60 gold 19.30 ice 0.92 iron 7.87 lead 11.35 paper 0.90 salt 2.17 sugar 1.58 wood balsa 0.15 wood oak 0.78 Liquids alcohol 0.79 milk 1.03 oil 0.90 petrol 0.72 seawater 1.02 water 1.00 Gasses Air 0.00129 carbondioxide 0.002 natural gas 0.0000833 oxygen 0.00143 water vapour 0.000598

The quantity density is rather important in chemistry. You will work with calculations involving

mass, volume and density rather often and you need to be able to transform units from small to big

and back again. In addition, it is important that you realize that density is a compound specific

characteristic. This means that if you know the density of a substance, you can look at table 2 to

find out whether it is one of those substances. You can also see from the size of the density what

the phase of the substance is. Gasses always have a very small density (fewer particles per litre),

while solids have many more particles per litre and therefore also more mass per litre and as such

a higher density.

Experiment 3

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Mixture or pure?

The densitiy of a substance is a specific

property of matter. If you know the density

of a substance, you can tell, using Table 2,

if it is one of the common substances from

Table 2. Properties of matter are properties

specific for a substance only made of that

specific material. All melting points and

boiling points (Table 1) and densities (Table

2) are specific for those substances. Of course it is possible to mix two or more pure substances,

which will give a mixture. This new substance, the mixture, has

completely different properties. Dissolving kitchen salt in water, you

observe the white kitchen salt disappearing in the water quite quickly.

But the water doesn’t seem to have changed. However, if you would

taste this water, you immediately notice the presence of the table

salt. The properties have changed: the white powder, the table salt,

has disappeared, but its taste is still present. Water has obtained taste, but it still is a colourless

liquid. In addition, properties of matter as melting point, boiling point and density also change for

mixtures, for instance notice the change in density of sea-water in comparison to pure water

(Table 2). We all know that sea-water will solidify at a temperature far below 0°C. That is because

sea-water doesn’t consist of one substance (water), but also contains a lot of salt. Mixing

substances gives a new substance with new properties and a different value for the substance

specific properties.

By looking at the properties of a substance you will receive information about:

• Which substance you have

• Is this substance a pure substance or a mixture

A mixture is a substance / a material consisting of two or more pure substances A pure substance only consists out of one type of substance

You can visualize the difference between a pure substance and a mixture well with coloured

marbles. Suppose you have a jar with only red marbles. This represents a pure substance, only

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red marbles. Another jar contains red, yellow and blue marbles, this jar represents a mixture.

Closing your eyes and taking one marble from the first jar you can be certain you picked a red

marble. All marbles in that jar are red ones! But if you take a marble from the second jar, you don’t

know which colour you will get: a red one, a yellow one or a blue one. In chemistry, the same

principle can be applied for substances, only we don’t work with marbles but with very small

particles like molecules. In the following paragraphs of this reader you will learn more about

mixtures and pure substances. You will learn how to recognise them with the eyes of a chemist.

Questions.

23) Explain what the difference is between a mixture and a pure substance. 24) Draw a model representation of the substances below. In this drawing each particle has

to be represented by a coloured ball. a. Pure water b. Sugar in water c. A mixture of iron and carbon d. Pure air

25) In the kitchen you see a container with a white powder. In this container usually one of the following substances is kept: sugar, kitchen salt or flour. Ian wants to know which of the three substances is kept in there at the moment and decides to do some experiments.

a. First of all he tries to dissolve the powder in water. The powder dissolves well. Which substance can therefore be excluded and why?

b. Secondly he heats the substance in a little dish. The white powder starts to bubble and the colour changes from white to yellowish brown. Which substance did Ian demonstrate?

c. Are there other ways of discriminating between these substances? 26) For the next assignment you need Table 2.

a. Calculate the mass of 3.21 litre of aluminium. b. Calculate the volume of 0.834 grams of oxygen. c. An object is made of a pure material, has a volume of 3 litres and a mass of

57.9 kg. Of which material is the object made? d. What is the mass of 2400 litres of air? e. What is the volume of 231g of gasoline (benzine)?

27) Trying to mix oil and water you will see they don’t mix. You will get two layers on top of each other. Which substance is the top layer and how do you know?

28) Why do people float more easily in the Dead Sea than in the North Sea?

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29) Someone finds a heavy, yellow metal bar. He thinks he is rich, he has found gold! He brings the bar to abuyer of gold. He receives the bad news that it only looks like gold, but it is actually mainly iron. Think of a workable way how the gold buyer has found out that the bar is not made of gold.

30) Go to the site: www.snapput.nl/video/stofeigenschappen. Watch the video and do the questions.

In paragraph 5 you have learned:

• What a substance is and what a substance characteristic is.

• Which phases a substance can have and what the names are of the phase transitions

• What a temperaturecurve is

• What density is and how it can be used

• What a pure substance is and what a mixture is

• How compound characteristics can be used to find out whether a substance is pure or a

mixture.

1.6 Pure substance or mixture?

In this paragraph you will learn a bit more about ‘pure substances’ and ‘mixtures’. You already

know that a pure substance consists of one kind of molecules. So a substance only containing

water molecules is pure water. But, if you dissolve only one little grain of salt in one litre of pure

water, this liquid is not pure anymore: you have a mixture of a lot of water and a little bit of salt.

The properties of this mixture barely change in comparison to pure water. The boiling point and

the taste are almost the same. But if you consider the chemical structure, you will find, next to

water particles, particles of salt, which are not present in pure water. As you dissolve more salt in

the water, the effect on the properties of the mixture will increase. The taste will be more salty and

the boiling point will rise.

From the beginning of this reader you already know what will happen if you heat ice. In Figure 5

you see this in a diagram. If you start heating pure ice, pure solid water, the temperature of the ice

will increase till the melting point is reached at 0°C. In the diagram you see that for some time the

temperature will stay at 0°C. The reason for this phenomenon is that the energy (the heat) you add

is used to melt the ice. At the moment all the ice has become liquid water, the added energy is

used to heat up the liquid water.

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Figure 5. temperature-time curve of a pure substance

So the temperature of the water increases. If you continue heating up the water, at a certain

moment the temperature of 100°C will be reached, the boiling point of water. At that moment, the

water will start to boil and all the added energy will be used to bring about the change of state from

a liquid to a gas. During the boiling, the temperature will be 100°C constantly. This is a property of

pure substances: during a the change of state like melting, boiling, solidifying and condensing the

temperature will remain constant. A pure substance has a melting point, boiling point, solidifying

point and a condensation point.

Figure 6. Temperature-time curve for a mixture of compounds

This will change when you do not have a pure substance anymore but a mixture. Figure 6 shows a

diagram which looks similar to the diagram in figure 5, but this time it is not a diagram for pure

water, but for a mixture, for instance icecream, which is a mixture of ice, sugar, pigments and

flavouring and other substances. Again, the temperature of the ice-cream rises when heated. But

at the moment the ice-cream starts melting you see something different in the diagram. During the

melting process the temperature of the ice-cream still increases! Why? Part of the energy you add

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to the ice-cream is used to melt the ice-cream, but another part of the added energy is used to

heat up the other substances within the ice-cream, the sugar and other substances added.

Therefore the temperature of the mixture rises slightly. So, the mixture has a melting range, not a

melting point. During melting, boiling, solidifying and condensing the temperature of a mixture will

still change. A mixture has a melting range, boiling range, solidifying range and a condensing

range. This way you can determine if a substance is a pure substance or a mixture: if the

temperature will be exactly the same during melting you know you have a pure substance, if the

temperature will change slightly, you know you have a mixture.

Questions.

31) Every substance has its own melting point and boiling point. Explain this. 32) a) At what temperature will water boil?

b) Does pure water has a boiling point or a boiling range?

c) Do the water molecules change during the process of boiling?

33) Figure 5 and 6 demonstrate the changes in temperature during melting and boiling of a pure substance and of a mixture. Draw similar diagrams for the condensing and solidifying of a pure substance and a mixture.

34) Draw the temperature-time curve (1000-3000 degrees Celsius) of pure iron. 35) Show how the temperature-time curve might change if you would add a bit of tin to the

pure iron.

In this paragraph you have learned:

• How a temperature-time curve works • What happens during the heating of a pure compound and a mixture • How you can determine whether a substance is made from only one type of molecule or not

Experiment 4

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1.7 Building stones of substances, kinds of atoms and elements

Building stones of molecules

But: what causes these molecules to be different? Why do sugar molecules dissolve in water and

oil molecules don’t? Why is rat poison deadly and what makes sugar sweet? Every substance has

specific properties and if the molecules change, so do the properties. Therefore, molecules have

to be made out of ‘something’ to make them specific and to be different from other molecules.

John Dalton, a scientist with a very broad interest, lived from 1766-1844, so

a long time ago! He thought about all different types of phenomena like the

wheather, colour-blindness ánd chemistry! He also wondered what was the

reason that molecules differ from each other. He considered that molecules

had to be built up by even smaller particles to make them all different, so

molecules could have different properties. He called those smaller particles

atoms (from the Greek atomos, non divisible) or elements.

The most important issues of Dalton’s theory of atoms are:

1. Molecules consist out of very tiny particles: atoms

2. All atoms of the same type are identical, i.e. have the same properties like size and mass

3. Atoms of different types have different properties like size and mass

4. Atoms are indivisible and indestructible.

In general the essence of Dalton’s theory remains valid, allthough his model has been adapted

quite a few times later on. Another scientist discovered, almost 100 years later, that even atoms

could be split up in even more tiny particles! You will learn about this later this year in module 4.

Nowadays more than 110 different elements are known. To distinguish one type of atom from

another, all atoms have their own name and symbol. Quite often the symbol is the first letter of the

name of that atom. But sometimes that letter is already used for a different type of atom and so

two letters are used. The first letter of the symbol always is a capital. The smallest atom known is

hydrogen with the symbol H. Helium also starts with H and therefore got a symbol with 2 letters:

He, a capital and a small letter. The tabular display of all the chemical elements is called the

Periodic table, see table 3.

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Table 3 Periodic Table

In Table 4 you see about 40 different atoms, their names and their symbols. You have to know

these names and their symbols ánd vice versa. So, if the symbol is given you have to state the

complete name of the atom and if the name is given the matching symbol. You don’t have to know

the Latin name (given between brackets), but sometimes this clarifies the symbol. You also have

to know if the atom is a metal or a non-metal. You will need this knowledge later this year.

Questions.

36) To practise for the quiz, you can use the following site (select the atoms you have to know):

http://education.jlab.org/elementflashcards/question.php

Practise regularly. Remember which elements are metals and which ones are non-metals. You don’t need to know the Latin names of the elements.

37) Complete the sentence below by filling in the next words in the proper spaces.

Atoms, molecules, particles, substances

All ………… around us are made up of very small ……….. also called ………….

These ………., however, are made up of even smaller building stones, the ……………….

38) Explain why it is impossible to talk about Coca cola molecules. 39) A group of students are discussing the reader. They are looking at figure 3 on page12.

Wilco claims each ball to be an atom. Ann disagrees: she claims each ball to be a molecule. Who is right? Explain your answer.

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Table 4. Names and symbols of important kinds of atoms

Kinds of atoms Metals Non-metals

Aluminium Al Argon Ar Noble gas

Barium Ba Helium He Noble gas

Calcium Ca Neon Ne Noble gas

Chromium Cr Bromine Br Halogen

Cobalt Co Chlorine Cl Halogen

Copper (Cuprum) Cu Iodine(Iodum) I Halogen

Gold (Aurum) Au Fluorine F Halogen

Iron (Ferrum) Fe Carbon (Carboneum) C

Lead (Plumbum) Pb Hydrogen H

Magnesium Mg Nitrogen (Nitrogenium) N

Manganese Mn Oxygen (Oxygenium) O

Mercury

(hydrargyrum)

Hg Phosphorus

(Phosphorus)

P

Nickel Ni Silicon Si

Platinum Pt Sulfur (Sulfur) S

Potassium K

Radium Ra

Silver (Argentum) Ag

Sodium Na

Tin (Stannum) Sn

Titanium Ti

Tungsten W

Uranium U

Zinc Zn

In paragraph 1.7 you have learned:

• That molecules are made from small particles called atoms.

• That we know more than 110 different atom types at the moment

• The symbols of the most common atoms

• What the periodic table is.

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1.8 Different types of substances

The properties of a substance are determined by the building stones of that substance: the

molecules. Because molecules exist of groups of atoms the properties of matter of that substance

is determined by the number and the way the atoms are structured within the molecule. What kind

of atoms the substance is built out of? In this paragraph we will look at the types of substances we

have on earth. Chemists grouped all substances on their properties and in this paragraph a

number of these groups will be discussed.

To start, you can split up all substances into two big groups:

1. Elements (the non-decomposable substances or elemental substances)

Some substances can be heated for a long time without them decompose or splitt up into

other substances. For instance, you can heat gold for a long time at a high temperature, but

you you will not produce a new substance. The gold may melt, but it still will be, molten

gold. Slightly over 100 elemental substances are known, for instance hydrogen, oxygen,

gold, iron and carbon. Elemental substances are made up out of one type of atom only. So:

elemental substances are made up of one type of atom only!

2. Compounds (the decomposable substances or non-elemental substances)

1. Most substances however will decompose into other substances by heating at a high

temperature (for a prolonged period of time), they are broken down into other substances.

These substances are called compounds or decomposable substances. So: compounds

are made up out of more than one type of atom, at least two different types of atom!

Almost all substances in nature are compounds. For instance aluminium doesn’t exist in nature as

aluminium the element, but as a compound, aluminium with oxygen in the ore bauxite. In nature,

only a small number of elemental substances exists. For instance: in the soil carbon (cokes), gold

and platinum occur as elemental substances and in the air oxygen and nitrogen occur as

elemental substances.

Elements (non-decomposable substances, elemental substances) are made up out of one type of atom only. These substances cannot splitt up into other substancese even when a lot of energy is added.

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Compounds (decomposable substances) are made up out of more than one type of atom. These substances splitt up into other substances when (a lot of) energy is added.

Another way to classify substances is by their properties into:

1. Metals; 2. Salts and 3. Molecular substances.

1. Metals

A metal is a substance in which only one kind of atom occurs, the kind of atom of that

metal. For instance: gold only contains gold atoms. So: metals are elements. About 80

kinds of atoms are classified as metals.

All metals:

• have a shiny surface

• conduct heat and electricity

• are malleable (sometimes only after heating)

• can, when molten, be mixed with other metals: alloys.

Well known alloys are solder, bronze and stainless

steel.

• don’t dissolve in water

• have a high melting and boiling point

2. Salts

Salts are substances in which at least two kinds of atom are present: at least one metal and

one non-metal atom. Therefor salts are decomposable substances (compounds). You know

salts as table salt (NaCl) or plaster (CaSO4.2H2O).

Salts:

• are mostly crystalline or powders

• are sometimes dissolvable in water

• have a high melting and boiling point

• conduct electricity if dissolved in water or molten

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3. Molecular substances

Molecular substances exist of molecules. There are over a million molecular substances.

Very well known examples are water, sugar and oil. Their molecules are made up out of

more than one kind of atoms and all these atoms are non-metals. So, like salts, molecular

compounds are decomposable compounds. The difference can be found in the type of

atoms: salts are always made of at least one metal and one non-metal, while molecules are

made of only non-metals.

Molecular substances:

• do not have a high melting and boiling point

• sometimes dissolve in water

• do not conduct electricity, not even when dissolved or molten

Each group has its own characteristic properties. Chemistry is mainly concerned with studying the

structure of substances at the molecular and atomic level and tries to explain, even to predict, the

properties of matter of a substance.

Questions.

40) In the text above the characteristics of metals, salts and molecular compounds are listed. From the results of an experiment you can conclude if a substance is a metal, a salt or a moleculair substance. Design such an experiment.

41) The group of metals can be subdivided into different categories. The metal gold (Au) goes into the categorie of precious (noble) metals.

a) Write down two other precious metals.

b) Why are these metals called ‘precious’?

c) Google which metals belong to the category of ‘heavy metals’.

d) Describe the dangers of heavy metals.

Pure or not?

Another way to classify substances according to their purity: 1. pure compounds and 2. mixtures. It

is not easy to obtain completely pure compounds. Most of the time a substance of we which we

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consider to be pure still contains a very small percentage of something else, an impurity, thus it is

a mixture. For instance, what we call pure water is made of about 99.5% of water molecules and

for 0.5% out of other particles like other molecules or salts. Most of the time, in daily life, we use

mixtures. Mixtures can be manufactured in such a way that the combination of molecules will have

the properties that are needed.

Types of mixtures.

It is a lot more difficult to predict the properties of a mixture. Quite a number of different mixtures

occur. The mixtures mentioned below you have to know ánd you have to be able to recognise

them.

1. A suspension is a cloudy mixture of a solid substance and a liquid. Quite often the

density of the solid substance is larger than that of the liquid. If so, the solid substance

will sink to the bottom this is called the sediment. Also a number of solid substances are

known with quite a small density. For instance some kinds of wood have a density of

around 0.75 kg/L and therefore float on the water surface. If you clearly see two layers

of a substance within a mixture you call it a heterogeneous mixture. Some solid

substances however don’t clearly float on the water, but neither do they sink to the

bottom. This happens when the densities of both substances are about equal and you

will get a homogeneous mixture in which the solid substance seems to floats within the

liquid. Think about a mixture of paint and mud.

If a mixture is thoroughly mixed you call this mixture a homogeneous mixture

If within a mixture more the one layer is observed, you call this

mixture a heterogeneous mixture

2. If you add sugar to water and you stir, you will see the grains of sugar getting smaller

and the amount of grains diminish. Finally it seems like the sugar has disappeared

completely. The mixture is transparent. But: if you taste the water you notice the sweet

taste. So the sugar is still present. Now you have a mixture in which the sugar is

completely mixed with the water, at a molecular level a homogeneous mixture. These

mixtures are called solutions. It is also possible to mix a liquid in a liquid or a gas in a

liquid these are also solutions, when homogenous.

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3. If small, solid particles of a substance are present in air you call it smoke. Smoke arises

at (big) fires: in the air small solid particles are present very harmful for your lungs. If this

smoke comes into contact with other objects, the solid particles will stick to these

objects.

4. A mixture of drops of a liquid in another liquid is called an emulsion. An emulsion is also

cloudy. But: after some time you will see two layers in this emulsion, because the liquid

with the lower density will be on top of the liquid with the higher density. A

hetereogeneous mixture. By using an additive, the separation will be delayed. Such an

additive is called an emulsifier. Well-known examples are

mayonnaise and cleansing cream.

5. A mist is finely divided liquid in a gas, for instance fog and your

deodorant!

6. A mixture of metals is called an alloy. Metals are almost always

solids and therefore difficult to mix. To make an alloy, both metals are molten and the

molten metals are thoroughly mixed into a homogeneous mixture. After cooling down

the mixture, a new substance is created with new properties. Solder is an alloy of tin and

lead and has a low melting point. After cooling down the solder is quite strong, so it is a

good material for soldering.

7. A gas enclosed in a liquid is called foam. Examples are bath foam and seafoam.

Concentration of a substance in a solution.

If you want to make sweet water, for instance for a lemonade, than you dissolve sugar in a certain

amount of water. The ratio sugar to water determines how sweet your lemonade will be. If you

take only a bit of sugar and a lot of water, your lemonade will not be that sweet and obviously, if

you take a lot of sugar in only a bit of water (often the preferred choice) you will get a very sweet

lemonade. Chemists call the amount of a substance dissolved in a solvent, the concentration of

the substance. The concentration is expressed in the unit mass per volume, simply because you

dissolve a certain amount of a substance (expressed in grams) in a certain amount of solvent

(expressed in litres). If you dissolve 2g of sugar in 1L water the concentration of sugar is 2g/L. If

you dissolve 2g of sugar to 2L, the concencentration will be 2g/2L = 1g/L. The unit should be

chosen in correspondence to the situation. If you measure the amount of sugar in Cola, the unit

g/L is used. However, if you consider the amount of alcohol that can be found in the blood of a

person, g/L is not appropriate, the order of magnitude is more like mg of alcohol per litre of blood.

The concentration will therefore be expressed in the unit mg/L.

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The concentration of a substance in a solution is the amount of that substance (in g) per litre of solution

So the concentration of a substance in a solution expresses the amount of that substance per litre

of mixture. A solution of sugar in water with a concentration of 2g/L tastes less sweet than a

solution of 2mg/L.

Concentration is also used as a measure to express acceptable impurities or amounts of

medication that is needed to be applied to a person. For instance, after a fire in a city people are

often recommended to close all windows and doors and to stay inside because the concentration

of dangerous compounds in the air had become too high during the fire.

Bottles with a suspension of antibiotics often carry a label with the

concentration of the active antibiotic, usually an amount of 0.25g

per 5ml suspension is used. If the suspension would have a

concentration of 2.5g per 5 ml it would mean that the patient has to

use 10 times less of the suspension this a too small amount to

administer easily. If too much of the suspension is applied it could

lead to serious negative effects.

While making a solution, you have to take into account the maximum amount of a substance that

can dissolve in 1 litre of the solvent. Saccharose (a type of sugar) has a maximum solubility of

200g in 100 mL at room temperature. If you try to dissolve more, let’s say 210g in 100mL of water,

you will notice that 10g remains behind as a solid, in the form of solid particles (suspension).The

temperature plays an important role in the process of dissolving. The higher the temperature of the

solvent the more of a solid solute dissolves. You can try the following at home: try to dissolve three

spoonfulls of sugar in a small cup of cold water and determine the time this will take. Do the same

with hot water. Yo will notice a big difference!

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Figure 7. Solubility-temperature curve

The correlation between temperature and solubility is depicted in figure 7 which shows the

maximum solubility of sacharose in 100ml water in correspondence to the temperature. At room

temperature (20oC) the maxiuml amount of sacharose that dissolves in 100 ml water is 200g, while

at 85oC this has increased to 400g.

Questions.

42) Explain, in a scientific way, why bath foam doesn’t sink to the bottom of your bath. 43) Mayonnaise is a mixture of vinegar and salad oil to which an egg yolk has been added.

Explain the role of the egg yolk. 44) Make a word-web with all underlined words on this paragraph. 45) On page 29 a bottle with the pink suspension of the antibiotic amoxil is shown. Can you

see the concentration of amoxil in this suspension on the label? 46) In the text it is mentioned that the concentration of antibiotics is often 0.25g/5ml of

suspension. Does this correspond to the amount mentioned on the bottle?

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47) Fill out the table:

Alloy Properties Components Properties

Solder

Tin

Lead

Brass

Bronze

Stainless steel

48) What is wrong in the following sentence: “The concentration of the alcohol in blood was 1,25mg”.

49) You dissolve 2.9 g sacharose in 1L of water. What will be the concentration of sacharose?

50) What will be the concentration if you dissolve the same amount of sacharose in 2.9L water?

51) Which solution of the previous two questions is the most concentrated? 52) Use figure 7 for the following questions

a) Joke dissolves 250 g sacharose in 100ml of water. What is the minimum temperature that the water should have?

b) What is the maximal amount of sacharose that can dissolve at 80oC? c) John tries to dissolve 500 g of sacharose in 125 ml at 80oC. Will John be

succesfull? d) How much sacharose will be left behind in the solid phase?

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e) Emma dissolves 375g of sacharose in 100ml water of 80oC. After this, she cools down the solution to a temperature of 45oC. How much sacharose will precipitate (crystalize to sacharose in the solid form)?

In paragraph 1.8 you have learned:

• Which types of mixtures there are

• What a concentration means

• How you can work with concentrations

1.9 Molecules, atoms and properties of matter

Molecular formulas.

By now you know that substances

consist of particles, molecules, and those

particles consist of atoms. So the

building stones of all substances are the 118 elements occurring on earth.

When you were younger, you’ve probably played with lego a lot. The little

blocks of lego are used as building blocks and if you have enough stones you can build the most

beautiful constructions. As you can see in the picture, the Colosseum in Rome has been

reconstructed with thousands of little lego blocks. By exactly placing the right blocks at the right

time on top of each other, such enormous construction could be realised. Building molecules can

be realised in a similar way. The atoms are forged together in a certain way: the number of atoms

ánd the type of atoms available ánd the order of the atoms determine the structure of the molecule

and the properties of that structure.

The structure of molecular substances.

Molecules are built up out of two or more non-metal atoms. For

instance water: water is built up out of two hydrogen atoms (symbol H)

and one oxygen atom (O). The notation for this molecule is H2O, and

we call this a molecular formula. The ‘2’ is smaller and a little lower down the line it is called

subscript. The subscript is the number of atoms within a molecule and always two or more. If you

36

want to indicate that you have 3 molecules of water, you put a 3 in front of the molecular formula.

This 3 is called the coëfficient. So: three molecules of water = 3 H2O. The coefficient indicates the

number of molecules.

Every water molecule looks the same. They are

identical. 2 hydrogen atoms holding on to one oxygen

atom. Taking up an addition oxygen in the molecule

would give a completely new molecule. The same for

taking away an hydrogen atom, this would lead to a

completely new particle with different characteristics.

We already know that molecules are very small. If you

want to indicate the number of molecules present in a

glass of water of 180 mL, you come up with the number

of 6.000.000.000.000.000.000.000.000H2O! 1

A molecular formula indicates which atoms and the number of atoms a molecule consists of

The subscript is the small and lower figure after a symbol of an atom, it indicates the number of atoms within the molecule

The coëfficient is put in front of the molecular formula and it indicates the number of molecules present

1 In comparison: suppose you would have a similar amount of moles (the small furry animals) these moles would take up enough space to make a second moon! https://what-if.xkcd.com/4/

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The phase in which the substance occurs is indicated by a letter between brackets.

• A solid is indicated by (s). So ice, solid water, is H2O(s)

• A liquid is indicated by (l). The substance alcohol has the molecular formula C2H6O, at

room temperature alcohol is a liquid and indicated by C2H6O(l).

• A gas is indicated by (g). The substance methane (an important part of natural gas) has the

molecular formula CH4 and is gaseous at room temperature, indicated by

CH4(g).

• A substance dissolved in water is indicated by (aq) aqueous. If you dissolve

pure acetic acid in water, you will get vinegar, C2H4O2(aq), a solution you use

as part of the salad dressing for a nice taste.

Questions

53. a) How many molecules are indicated by 6H2O?

b) How many oxygen atoms are present in H2O?

c) How many oxygen atoms are present in 6H2O?

d) How many hydrogen atoms are present in 12H2O?

e) Draw 3H2O(g).

54. Look at the drawing in Figure 3 (page 12), but don’t use little balls as particles, but use the molecular structures of water. You have to draw at least five molecules.

55. a) Glucose is a molecule consisting of 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. What is the molecular formula of glucose?

b) How do you indicate six glucose molecules as a solid?

c) Why do you think chemists prefer molecular formula’s in stead of words?

56. Given: the notation 3C6Cl5OH. Answer the following questions.

a) What number has the coefficient?

b)What exactly is indicated by the coefficient?

c)What types of atom are present within these molecules?

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d)How do you call the figure ‘6’ in this formula?

e) In total, how many atoms of chlorine are present within this chemical notation?

f) In total, how many atoms are present within this notation?

57. Sulphuric acid is a compound with the molecular formula H2SO4. In words, the notation 2H2SO4 means: two molecules of sulphuric acid are present and each molecule consists out of 2 hydrogen atoms, one sulphur atom and 4 oxygen atoms. So in total the notation shows 4 hydrogen atoms, 2 sulphur atoms and 8 oxygen atoms. Do a similar description for:

a) 4CO (carbonmonoxide) b) 3NH3 (ammonia) c) 5C2H6O (ethanol)

Molecular formula becomes structural formula.

A molecular formula is a formula which shows the number of atoms of each element in a molecule

of a compound. A structural formula indicates how all these atoms are grouped together. A line

indicates how two atoms are connected = bonded. The water molecule has three building blocks,

2x an H en 1x an O. You can connect these three building blocks in two ways: H-H-O en H-O-H.

The second way is the right one. We will explain in more detail why this is the case in reader 4. A

drawing of a molecule showing how the atoms are bonded can be represented in different ways:

Figure 8.

Two other ways of showing structures are the “ball-and-stick” model and the space-filling model. In

the last one the connection lines are left out and the atoms are ‘fused together’ to indicate

bonding.

The elements a molecule consist of, the number of atoms and how they are grouped together

(structure) determines the properties of the molecule to a very high degree. One atom more or

less really makes a hugh difference! Lets compare the following two molecules with each other:

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H2O en H2O2, respectively water and hydrogenperoxide. We know water is a liquid at room

temperature, you can drink it and you can have a nice hot shower using water. The molecular

formula of hydrogenperoxide looks a lot like the one of water. Hydrogenperoxide has only one

extra O atom, making the molecular formula H2O2. The presence of this extra O atom gives the

substance completely different properties. It still is a liquid at room temperature and also

colourless.

Figure 9. H2O2 H2O

But: the addition of an extra O atom, makes hydrogenperoxide a poisonous substances compared

to water. One drop of hydrogenperoxide can damage your skin depending on it’s concentration.

And: if you make a solution of a little hydrogenperoxide in water, you can bleach hair, so

somebody with dark hair will look completely different after applying hydogenperoxide!

The constants of substances are completely changed. The melting point, boiling point and density

of water and hydrogenperoxide are completely different!

A structural formula shows in a drawing how the atoms in the molecular formula are bonded.

At the moment you don’t know a lot of chemical structures and you certainly don’t know these

structures by heart. Don’t worry, by using them you will get to know more of them in the near

future. At the end of the year, in module 4, we will discuss in more detail how molecules are made

and how atoms are bonded to each other.

Questions

58) Google water and hydrogenperoxide and find at least six different properties. Put these properties in a table and compare them. Are water and hydrogenperoxide quite different in their structure? And in their properties?

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59) Below you see the drawings of a molecule of ethanol, a molecule of acetic acid and a molecule of propane. A black ball is a carbon atom, a red ball an oxygen atom and a white one is a hydrogen atom.

Ethanol Acetic acid Propane

a) What is the difference between a propane molecule and the two other ones? b) What is the difference between acetic acid and ethanol? c) Give the molecular formula of these three compounds.

60) Testosterone is a male sex hormone. During puberty, the amount of this hormone increases and sometimes makes boys do what they do during puberty. The structural formula of testosterone is given below. The black balls indicate a carbon atom, the white balls a hydrogen atom and the red one an oxygen atom.

a) According to Wikipedia the molecular formula of testosterone is C19H28O2. Correct?

b) If these atoms are arranged in the way as above, you will get the molecule testosterone as we know it, with all the properties we know of this molecule. Do you expect the properties of a substance in which only one atom is different to be changed a lot? Explain your answer.

61) Look at the three pictures below.

a) Which of the three substances is a pure substance?

b) Which picture demonstrates a mixture?

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c) How many different molecules are shown?

d) How many different atoms are shown?

In paragraph 1.9 you have learned:

• What a molecular formula is

• What the index and the coefficient mean with molecular formulas

• How one has to indicate the phase in a molecular formula

• What a structural formula is

In daily life most substances we use are mixtures. In fact it is quite difficult to get a substance that

is completely pure and quite often it is not necessary. But sometimes we do want a substance to

be100% pure. Imagine yourself as a worker in a factory making medicines. Medicines should be

pure, at least without detrimental substances. To do so, chemists use separation techniques. You

will learn more about these techniques in the next paragraph.

A B C

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1.10 Separation of mixtures: making use of the differences in properties of matter

In separating mixtures, we split up the mixture into its pure substances by making use of the

differences in properties of both substances. So, in separating a mixture, you are sorting the

different molecules from each other. The substances do not change itself and the molecules

remain unchanged. We simply separate the mixture into it’s pure substances. Figure 10 shows the

separation of a salt water mixture into water and salt.

= water

= salt

Figure 10. Separation of substances

In order to be able to separate molecules from a mixture into the pure substances we can use a

number of separation techniques which make use of the different specific properties of the

molecules in the mixture.

In this paragraph you will learn about the separation techniques:

• Filtration/decantation

• Extraction

• Evaporation

• Distillation

• Adsorbtion

Filtration and decantation

In filtration and decantation you make use of the difference in size of the particles in the mixture.

Grains of sand are big particles in comparison to the water and sand molecules so if you run a

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mixture of sand and salty water through a filter, the big

grains of sand will stay in the filter and the small water and

salt molecules will pass through the filter.

This way you have separated the grains of sand from the

salty water by using the difference in size between the

particles. The liquid passing through the filter is called the

filtrate and the particles remaining on the filter the residue.

A similar technique is called decantation. Suppose you

have a mixture of a solid in a liquid, for instance sand in

water. The sand will slowly sink to the bottom and is called

sediment. The liquid on top of the sediment can be poured

off, very carefully. This is called decantation.

Figure 11. Filtration

Extraction

Extraction is based on the difference in solubility of the substances

in the mixture. Suppose you have a mixture of salt and sand and

you want to remove the salt from the sand. By now you know salt

will dissolve in water and sand does not. You add water to the salty

sand the salt will dissolve, the sand does not. By filtration you can

purify the sand from the salty water. The liquid, in this case water,

is called extraction solvent, the water containing the salt is called

the extract. This technique is used a lot in obtaining salt from the

earth. But also in making a cup of tea or coffee!

Experiment 5

Evaporation

After the extraction you are left with water containing salt. Suppose you are interested in the salt.

How to obtain the salt? Evaporation is based on the diffenrence in boiling point. Water boils at

100°C, salt only boils at 1465°C and it only melts at 801°C! Heating the saline mixture for some

time at a temperature below 800°C but above 100°C, the water will evaporate and the pure salt

will be left.

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Figure 12. Evaporation

Distillation

In distillation is also based on the difference in boiling point. Only, this time you are interested in

obtaining the liquid, unlike the evaporation above. Suppose you have wine, a mixture of water and

alcohol (ethanol). You are interested in the ethanol as a pure substance. Evaporation will not be of

any help because if you heat the mixture it will result in the evaporation of the ethanol. The

substance with the lower boiling point. The boiling point of ethanol is 78.4°C quite close to the

boiling point of water.

Adding the mixture in the distillation flask (kolf) (Figure 13). In heating the distillation flask slowly,

the boiling point of ethanol will be reached before the boiling point of water. The molecules of

ethanol will become gaseous, and go up the flask and down into the cooler and condensate again

as the temperature of the cooler is around 20°C. This way you will get the pure condensated

ethanol in the erlenmeyer flask. In the distillation flask less and less ethanol will remain and mainly

water will be left. You call this the residue. The pure ethanol you get in the erlenmeyer flask is

called the distillate.

Figure 13. Distillation of wine

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Adsorbtion.

Some mixtures contain pigments, flavouring and / or aromatic substances. These are very difficult

to remove from a mixture by extraction or distillation. By adding tiny grains of carbon (Norit, active

coal) you can remove these substances easily. This technique is called adsorption. Because the

carbon grains are really tiny and also have little holes in them, the surface area is huge. The

dissolved pigments, flavouring and aromatic substances can go into these little holes and stick to

the surface of the carbon grains. After filtration the active coal with all the pigments, flavouring

and aromatic substances will remain on the filter paper as the residue. The filtrate will the pure

liquid, without these annoying substances.

Experiment 6

Assignments.

62) Google ‘alembic’. This technique preceded one of the separation techniques you just learnt. Which one? Explain the advantages of this new technique in comparison to alembic.

63) Explain why extraction is not a chemical reaction.

64) Explain which technique or combination of techniques you would use to separate the following mixtures:

a) pigments (color molecules) in water

b) tea-leaves from tea

c) flavouring agents from coffee-beans

65) Look up (internet) the boiling points of ethylacetate, diethylether and hexane.

Design an experiment to separate these three substances in a mixture into three pure substances.

66) Look up (internet) which separation techniques are used to purify groundwater and surface water into pure tapwater.

67) For the purification of alcohol, distillation is used and not evaporation. Give two reasons for this.

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So purification of a mixture means that you separate different molecules from each other by

making use of their characteristics like phase, solubility, boiling point and adhesion capability. In

the following experiment you will be asked to use the techniques described above to separate a

mixture of three different compounds. Make your own workplan for this! Good luck.

Experiment 7

You have learned in this paragraph:

• What a purification is

• That during a purification compounds are separated from each others, not the atoms from

the particles

• Which purification ways we can use

• How to separate a mixture of three substances

Final conclusion

Now you’ve come to the end of Reader 1.

Youy have learnt a lot of new things:

• You can explain what the difference is between biology, chemistry and physics

• You can explain (and give examples of) reversible and irreversible changes

• You know how doing research works, you understand the research cycle.

• You know what a research question is and what a hypothesis is.

• You know the safety rules

• You know which safety rule has tob e used in which occasion

• You know the parts of a report

• You can explain what a substance is

• You know what substance properties are.

• You can use properties for explaining which compound you have in a flask

• You can do calculations with density

• You can work with boiling and melting points.

• You can use table 1 and 2 for the determination of the identity of a substance

• You know what molecules and atoms are

• You can explain the difference between pure and not pure

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• You understand the calculations with concentration and you can work with solubility graphs

• You know the most common separation techniques

In the last paragraph a number of questions are given like the ones you can expect on the test.

Practise these questions well!

1.11 Concluding: test-yourself.

1) The coldest temperature ever recorded on earth is -89°C on the antarctic. The melting point of oxygen is -219°C and the boiling point is -183°C. Explain if the amount of oxygen in the air has become less at -89°C.

2) Jasper claims that the sugar bought in the shop is a pure substance. Kees disagrees and says no, it is a mixture.

a) Do you agree with Jasper or Kees? Explain why. Or do you think it is not possible to know if sugar is pure or not? Explain your answer.

b) Thereupon Kees explains why he thinks sugar is a mixture. He googled ‘sugar’ and found the molecular formula for sugar: C12H22O11. So to him it is clear sugar is a mixture. Explain if this true or false.

c) How many carbon atoms are there in one molecule of sugar?

d) How do you write down six molecules of sugar in the solid state?

3) a) Give the names of the following symbols: Au; Ag; Ne; Cl; C; H

b) Give the symbols of the following kinds of atom: copper, nickel, argon, bromine, nitrogen, oxygen

4) a) Write down 4 general characteristics of metals.

b) Write down 3 characteristics of metals which clearly make them differ from water.

c) Write down 3 characteristics of metals which clearly make them differ from salts.

d) What is an alloy? Explain.

5) Cooking utensils quite often are made of stainless steel. This is an alloy of iron, nickel and chromium.

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a) Give the symbols for these kinds of atom.

b) What is the advantage of stainless steel? Explain!

6) a) Draw a homogeneous mixture of salt and water. Use a little coloured ball for salt and a different coloured one for water.

b) What would a drawing of a heterogeneous mixture of salt and sand look like? Again, use different coloured balls for sand and salt.

c) How would you separate a mixture of sand and salt? Explain.

7) Describe briefly the difference between evaporation and distillation. Which technique is used in which situation?

8) Debby has a warm, liquid substance. During the cooling down of this liquid, she measures the temperature of the liquid every 30 seconds. She plots her data in a graph. What would the graph look like?

9) In this chapter you learned to notate molecules in two different ways: as a drawing or as a formula. When is best to use a drawing? Explain.

10) Calculate the mass of 344 ml oxygen. Show your workings.

11) Calculate the volume of 1.2kg of lead. Show your workings.

12) a) A company makes a new painkiller pill (oral intake), one that works exceptionally well against the pain caused by migraine (severe headaches). What do you think, is this painkiller soluble in water?

b) Yosemite dissolves 212mg of the painkiller in 2.3 ml of water. Calculate the concentration of this solution expressed in mg/ml.

c) Express the answer of question b) in mg/L

d) The maximum solubility of this painkiller in water is 100mg/ml at 25oC. What would happen if you try to dissolve 212mg of the painkiller in 1.5 ml water of 25oC?

13) In the graph on the next page you see four solubilitycurves.

a) Explain why the curve goes from low solubility to a higher solubility.

b) Of which of the 4 compounds shown in the graph is the influence on the solubility the most pronounced?

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c)How much KNO3 is soluble at 60oC?

d) What happens if you dissolve 130g of KBr in 200ml water at 70oC?

e) What happens if you dissolve 130g of KBr in 100ml water at 70oC?

f) What happens if you dissolve 90g of KBr in 100ml water at 70oC?

g) What happens if you dissolve 90g of KBr in 100ml water at 70oC and subsequently coll down to 50oC?

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Experiment 1 Bunsen burner-experiment

Research question:

How does the burner operate?

Theory

In the Bunsen-burner natural gas is mixed with air. After heating this mixture, for instance with a match, it will ignite and burn. In the figure you see a cross-sectional drawing of the burner. With the gas regular knob you can handle the supply of natural gas and with the air regulator thumbwheel the supply of air.

Special safety precautions

– Fasten the wooden test tube holder at the top of the test tube. If you fasten it lower, you run the risk of setting the wooden test tube holder on fire.

– When heating a liquid, you regularly have to move the test tube a little bit. If you don’t do so, you run the risk of getting a boiling liquid at the bottom of the test tube resulting in a splashing liquid.

You need:

– burner – gauze – tongs

– matches – test tube holder – test tube stand

– 2 test tubes – wash bottle with demineralised or distilled water

This experiment consists of 5 parts.

1. Light the burner.

– Turn up the air regulator thumbwheel completely.

– Shut off the gas regulator knob completely.

– Open the gas supply on the bench (yellow knob).

– Keep a burning match slightly above the burner.

– Open the gas regulator knob slightly and light the burner.

– Note the colour and the sound of the flame and write these observations down on the following page.

2. Regulate the colour of the flame.

– Open the air regulator thumbwheel just a little bit to get an colourless (slightly blue) and soundless flame.

– Open the air regulator thumbwheel a bit more to get a roaring blue flame.

– Write down these observations in the table.

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The air regulator thumbwheel Colour of the flame Roaring sound?

Up (closed)

Halfway: a little bit opened

Down: completely opened

3. Regulate the size of the flame.

– The burner should be on with a soundless and colourless flame.

– Slowly turn the gas regulator knob up and down again.

4. Check the where the roaring blue flame reaches the highest temperature.

– Get a roaring blue flame.

– Keep, with tongs, a gauze horizontally in the blue roaring flame.

– Write down, in the table on the next page, the colour of the gauze at three different heights:

a in the blue cone;

b exactly on top of the blue cone;

c above the blue cone.

location colour of the gauze conclusion about temperature

in the blue cone

on top of the blue cone

above the blue cone

5. Heat a liquid in a test tube.

– Before you start, carefully read the second remark of the special safety precautions. This remark concerns the heating of a liquid in a test tube.

– Into two test tubes, put water from a wash bottle up to about 4 cm.

– Thoroughly dry the outside of the test tubes.

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– Heat one of the test tubes in the yellow flame until the water boils.

– Heat the other test tube in a non-roaring blue flame until the water boils.

– Write down in the table on the next page in which test tube the water boils fastest.

– Note the colour of the outside of both test tubes after finishing the experiment and write down your observations in the table on the next page.

flame Time, fastest or slowest, until the water boils?

Colour of the outside of the test tube after the experiment?

conclusion

yellow flame

colourless blue flame

6. Turn off the burner.

– Completely turn up the air regulator thumbwheel.

– Turn off the gas regulator knob.

– Turn off the gas supply on the bench.

Logbook Experiment 1

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Experiment 2 Substances: how to identify them.

Research question

How to recognise a substance?

Theory

You can identify substances by their differences in properties. Is the substance a gas, a liquid or a solid at room temperature? What is the colour? Does the substance smell? Can you dissolve it in water or in another liquid, is it flammable? In this experiment you are going to identify five white, solid substances by using their differences in properties. You are also going classify the substance as a metal, a salt or a molecular substance. Can you tell if the substance is a decomposable substance or not?

Special safety precautions

Maybe some of the substances are quite flammable. So always keep the spoon on top of heat-resisting material, like the tile. Be careful: the spoon which you use to burn the substance is still hot when you take it out of the flame. Don’t get burned!!

You need:

– burner – matches – metal spoon

– heat-resisting material (for instance a tile) – tissues – spatula

– wash bottle with demineralised water – five test tubes, numbered 1 to 5

– five white substances:

calciumcarbonate (chalk), citric acid, sodiumchloride (kitchen salt), camphor and glucose (grape sugar or dextrose)

You have to:

Investigate the properties of the five substances.

Therefor you have to perform four experiments with all five substances. Write down your observations and conclusions in the Table on the next page.

– Experiment 2.1

Have a close look at the substance. Describe the substance as well as you can. For instance, is the substance a real powder or does it have crystals? Small crystals or large crystals? Write down your observations in the table on the next page.

– Experiment 2.2

Smell the substance carefully by wafting. Never put your nose immediately on top of the test tube! Write down the smell in the table.

– Experiment 2.3

Put a little bit of the substance on the spoon and heat it carefully using the non-roaring blue flame. If you think the substance is burning, take the spoon out of the flame for a short period of time and return it to the flame.

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Repeat. If the substance is still burning when taken outside the flame, it is a flammable substance. Write down your observations for each flammable substance as well as you can in the table, for instance how the substance burns.

After every experiment you have to rinse the spoon with demineralised water and clean it with a tissue.

– Experiment 2.4

Put about 1 to 2 cm demineralised water in a test tube an shake carefully for a couple of minutes, holding the test tube at the top. Write down in the table on the next page if the substance is dissolvable in water.

Be carefull, some substances might be flammable!

Logbook:

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Observations and Conclusion

number of the substance

Experiments

Experiment 1

What does the substance look like?

Experiment 2

What type of smell has the substance?

Experiment 3

Is the substance flammable? What else do you notice?

Experiment 4

Does the substance dissolve in water?

Conclusion

Salt, metal or molecular substance?

1

2

3

4

5

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Experiment 3

A mixture of solid substances

-Mix two, differently coloured, types of chalk. Has the colour of the mixture changed completely?

-Are the two colours you started off with completely vanished?

-Use a microscope to find out what happened to the two colours.

-Are the particles you see, using the microscope, molecules?

Logbook experiment 3

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Experiment 4 Pure substance or mixture?

Research question

You get two substances. Which one is the pure substance and which one is the mixture and how can you demonstrate this?

Theory

During melting and boiling the temperature of a pure substance doesn’t change. A pure substance has a melting point and a boiling point. During melting and boiling the temperature of a mixture will change slowly. A mixture has a melting range and a boiling range. So by continuously measuring the temperature of a solidifying sample, you can determine if the sample is a pure substance or a mixture.

Special safety precautions

You will do this experiment with hot test tubes. Take are!

You need: – water bath – 2 test tubes – thermometer

– test tube stand – 5 gram beeswax – 5 gram palmitic acid

– stopwatch

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Logbook experiment 4

You have to:

1 Take the test tube with the molten substance 1 from the water bath and immediately read off the temperature. This is the temperature at t=0.

2 Read of the temperature every 30 seconds for 6 minutes

3 Write down your observations. When do you observe the first crystals? When is the liquid completely solidified?

4 Repeat all of the above with substance 2.

5 Make one table for substance 1 and 2 with all your results, observations and conclusion.

6 Draw for both substances a temperature-time diagram.

Observations and conclusion:

sample Observations in the temperature-time diagram: temperature course during solidifying.

Conclusion: pure substance or mixture?

Palmitic acid

beeswax

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Experiment 5 Sand from Zandvoort?

Research question

Which of the two samples of sand is taken in Zandvoort?

Theory

Sand coming from the beach always contains a bit of salt, sand coming from the inland does not. By using three separation techniques, extraction, filtration and evaporation, you can separate the salt from the mixture and obtain it as a pure, solid substance. This way you can determine if a sample of sand actually was takes from the beach or for instance from the Veluwe.

Special safety precautions

In this experiment you work according to the safety precautions you have to follow working with a bunsen-burner. Make sure you have a small blue flame only when you evaporate the filtrate in the evaporation disk. Otherwise you may get a lot of splashing! Don’t try it.

You need:

– burner, matches – tripod – gauze

– evaporation disc – tongs – two beakers, 50 mL

– glass rodd to stirr – two test tubes – test tube stand

– funnel – filter paper – wash bottle with demineralised water

– 10 mL sand sample l – 10 mL sand sample ll

You have to:

1 Extraction

– Put a little water in each of the beakers with the sand samples.

– Stirr the mixture with the glass rod, in both beakers.

2 Filtration

– Put a mark on the test tubes, I and II.

– Fold the filter paper and put it in the funnel.

– Put the funnel on top of test tube I.

– Pour the contents of beaker I in the funnel.

– Wash the the beaker with a little bit of demineralised water and also pour these contents in the funnel.

– Repeat the procedure for beaker II with the sand sample II. Use test tube II.

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3 Evaporation

– Put the evaporation disc on the gauze on the tripod.

– Pour (part of) the contents of test tube I in the evaporation disc.

Make sure the evaporation disc is only filled halfway.

– Ignite the burner, make sure the flame is halfway maximally, put the burner underneath the evaporation disc and evaporate the liquid completely.

– Repeat this procedure for test tube II.

Observations and conclusion

Sample of sand observations conclusion: salt in the sample?

I

II

Experiment 6

How to discolour a colored solution with Norit?

Research question

How to remove the colour from methylated spirit or another coloured solution?

Theory

Liquids may hold dissolved pigments, flavouring and / or aromatic substances. To remove these substances from the liquid you can add active coal, Norit. The active coal consists of tiny grains of carbon with holes in them and in the holes of each tiny grain these substances can be bound to the active coal. The technique is called adsorption. Thereafter you can separate the active coal from the liquid by filtration: the annoying substances, together with the

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active coal, will remain in the filter. In this experiment you are going to remove the blue colour from methylated spirit with active coal.

You need:

– test tube stand – test tubes – bung

– funnel – filter paper – spatula

– active coal (Norit) – methylated spirit

You have to:

1 Fill two test tubes halfway with methylated spirit.

2 Filtrate the contents of the first test tube using the filter paper and the funnel. Collect the filtrate in a test tube.

3 Add a spatula of active coal to the second test tube. Put the bung on top of the test tube and shake well but carefully.

4 Filtrate the suspension of methylated spirit and Norit and collect the filtrate in a test tube.

5 Compare the filtrate from ‘2’ with the one of ‘4’.

Observations and conclusions:

Note down your observations and conclusions in the logbook. Also answer the following 3 questions.

1 Is filtration only enough to remove the blue colouring from the methylated spirit?

2 How did you remove the blue colouring from the methylated spirit?

3 Which separation technique did you use to remove the blue colouring from the methylated spirit?

Logbook experiment 6

Clean up

The filter papers with Norit go into the bin. Ask the TOA what to do with the other materials used.

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Experiment 7. Dossierexperiment Report (1x)

You have a mixture of three solid substances: sand, salt and iodine. You also have three solvents: water, hexane and ethanol.

The solubility of the three solid substances is as follows: sand doesn’t dissolve in any of the solvents. Salt barely dissolves in ethanol, not at all in hexane and quite well in water. Iodine barely dissolves in ethanol, badly in water and quite well in hexane.

Using these data, set up an experimental design for an experiment to separate these three solid substances. Before you start the experiment, have your teacher or the TOA approve of your experimental design.

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Additional Assignments

https://www.youtube.com/watch?v=pzHiVGeevZE

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Assignment 1

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Assignment 2

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Assignment 3

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Assignment 4

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Assignment 5

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