Topic 1.2: Experimental Chemistry

Learning outcome

1.5 Laboratory Rules and Precautions

A laboratory rule is what must or must not be done inside a laboratory.

Laboratory Precautions are steps taken by a laboratory user in order to avoid accidents while

inside a laboratory.

Or Laboratory rules are dos and don’ts that are observed in the laboratory in order to avoid

accidents

After you have studied this topic, you will be able to:

1. Know laboratory rules and regulations and understand the importance of

risk assessment in order to work safely. Know action required incase of

accident.

2. Know and use laboratory equipment appropriately for measuring time,

temperature, mass, volume.

3. Understand the scientific method to carry out investigations and

importance of risk assessment to keep self and others safe.

4. Know how to purify mixtures, basing on information given

5. Know how to purify substances and their purity by using their melting and

boiling points

Student’s task 2.1

(i) The table below shows the laboratory rules and precautions, by “writing rule or precaution”

against each statement, indicate which one is a rule and which one is a precaution.

Rules or PrecautionsWhy is it necessary to observe the rule/take the precaution(which danger/accident is being avoided)

1 Keep your place of work tidy and clean

2 Tie up long hair and tuck in ties and loose clothing

3 Ask if you are not sure of anything

4 Keep the bottle below eye level when pouring liquid from bottle

5 Use test-tube holder whenever you

are heating from a test tube

6 Heat only at the bottom of the test

tube

7 Always collect solutions with a measuring cylinder or graduated container

8 All containers must be clearly labeled before collecting chemicals

9 Read practical instructions carefully before you begin on any practical

10 Record your results immediately by

use of a pen

11 Dismantle the apparatus before you

leave the laboratory

12 Keep bags, coats and books safely out

of the way

13 Never run inside the laboratory

14 Never eat or drink in the laboratory

15 Never play with fire, electrical

switches or chemicals

16 Never look down a test tube that is being heated or point it at your neighbor

17 Never overload spatula with chemicals

18 Avoid wasting chemicals

Student’s task 2.2

A group of five students is required to carry out a practical activity of recovering salt that had accidently got mixed with sea sand.

As a member of this group of five;

i) List the materials would require to successfully carry out the activityii) Explain the procedure, highlighting all precautions required, you would undertake in

this activity (diagrams may be used for better illustrations)

An apparatusis a tool (or equipment) that is used in the laboratory to carry out experiments. This tool could be glass, wood, plastic or rubber.Chemistry practical work employs a wide range of apparatus. School chemistry laboratories are usually stocked with the common simple laboratory apparatus.Below are some of the apparatus used in a chemistry laboratory:

Plastic beakers, wash bottles. Desiccators Separating funnels Fractional distillation apparatus

Bunsen burner Triple beam balance Digital weighing balance

Retort stand, Clamp, boss holder. Pair of tongs, motor & pestle Test tubes, volumetric flasks Conical flask

Students Task 2.3

Identify and give the use for each of the following named apparatus

Apparatus Description of use in relation to material(s) from which its made

Wash bottle

Boiling tube

Beehive

Delivery tube

Filter funnel

Test tube

Water trough

Gas jar

Thistle funnel

Tap/ dropping funnel

Flat bottom volumetric flask

Stirring rod

Motor and pestle

Pair of tongs

Pipette

Round bottom volumetric flask

Separating

funnel

Flagrating spoon /burning

spoon

Test-tube holder

Stirring rod

Tripod stand

U-tube

Heating Apparatus in the laboratory

Laboratory heating apparatuses

The chimney

The collar

The base

The air hole Gas tube

The Bunsen burner

2.1 Structure of the Bunsen burner

This is a heating apparatus that uses butane fuel gas in the laboratory. It was invented in 1854 by a German chemist called by Wilhelm Bunsen.The Bunsen burner has four main externally visible parts;

1. The base. 2. The chimney. 3. The collar. 4. The air holeDiagram of a Bunsen burner showing the main externally visible parts

Task 2.4

Bunsen BurnerThe Bunsen burner is one of the most well-known pieces of laboratory equipment found within school science labs. It consists of a mixing tube which is used to generate a mixture of gas and air. Once lit, the intensity of the flame can be varied by opening or closing an adjustable air hole. Bunsen burners are typically used to heat beakers of liquid in order to induce chemical reactions. Bunsen burners also pose disadvantages: They cannot control the temperature as accurately as electronic heaters and using an open flame can be dangerous.Laboratory OvenYou use a laboratory oven to heat samples (usually solids) to a set temperature, for a given amount of time, within an enclosed environment

Laboratory IncubatorYou use a laboratory incubator to heat a biological

Gas from the gas tap

The Jet

A:………………………..

B:…………………..……

C:…………………………

Diagram showing the Structure of a Bunsen Bur ner in a longitudinal section

Students Task: Name the unlabeled parts A,B and C of the Bunsen burner

Task 2.5

Explain the functions of the main parts of a Bunsen burner

Part Use of the main part

The Flange

The Chimney

The collar

The air hole

The jet

The base

Lighting a Bunsen burner To avoid fire accidents, a Bunsen burner must be lit following a particular sequence of steps. The steps are;

(i) Connect the Bunsen burner to the gas tap by use of gas tubing.(ii) Close the air hole of the Bunsen burner(iii) Open the gas tap(iv) Apply a lighted splint to the top of the chimney.(v) Slowly open the air hole of the Bunsen burner.

Students self assessmentSuggest a sequence of four steps you would follow to put out a Bunsen flame

Caution: The commonest accidents associated with a Bunsen burner, is burning backBurning back is the tendency for a Bunsen flame to burn inside a chimney at the jet. This can cause a fire accident. To avoid burning back, students should follow the sequence of lighting out a bunsen burner2.3 Bunsen Flames

A flame is a mass of burning gas, which gives out light and heat.A burner produces two types of flames namely:

(i) Luminous flame (ii) Non-luminous flameLuminous Flame Non-luminous flame

This is a sooty yellow flame that is easily visible. A luminous flame is produced when the air hole of a Bunsen burner closed.

This is a non-sooty pale blue flame, which is faintly visible. A non-luminous aflame is produced when the air hole of a Bunsen burner is open

Yellow Zone

Zone of unburnt gas

Blue Zone

Part of Chimney

Luminous Zone(Orange)

Pale blue Outer zone

Blue Intermediate Zone

Zone of unburnt gas

Part of Chimney

Hottest part of the FlameX

Structure of a luminous flame Structure of non-luminous flame

Student’s task 2.6

a) Explain 5 differences between a luminous and non luminous flame

b) Charcoal and paraffin stoves are common heating apparatuses in our homes. Basing on

nature of fuels the stoves use and flames produced write a sensitization message to fellow

students highlighting;

i) Nature and source of fuel used by each heating apparatus

ii) Their appropriate use

iii) Precautions to be taken when used

Advantages of using a Bunsen burner for heating in the laboratory (i) It produces a very hot flame(ii) Its flame can be adjusted without necessarily turning it off(iii) It produces a flame without soot (a clean flame)(iv) It is light and portable(v) It is easy to light(vi) It uses a relatively cheap fuel gas.

Let’s think about it

What is common cause of fire accidents in a home

Fire Triangle This is a triangular representation of the three conditions for fire to burn.

(a) Complete the fire triangle by naming part A.

Heat A

Fire

Fuel

2.5 Fire ExtinguishersA fire extinguisher is an active fire protection device used to extinguish fire in emergency

situations.

Fire fighting foam

Dry Chemical fire extinguishers extinguish the fire primarily by interrupting the chemical reaction of the fire triangle.

Wet Chemical is a new agent that extinguishes the fire by removing the heat of the fire triangle and prevents re-ignition by creating a barrier between the oxygen and fuel elements.

Halogenated or Clean Agent extinguishers include the halon agents as well as the newer and less ozone depleting halocarbon agents. They extinguish the fire by interrupting the chemical reaction of the fire triangle.

Water Mist extinguishers are a recent development that extinguish the fire by taking away the heat element of the fire triangle. They are an alternative to the clean agent extinguishers where contamination is a concern.

Which chemicals are used in fire extinguishers?Nitrogen, carbon dioxide, potassium bicarbonate, liquid water, fluorocarbon like bromo diflouro methane

Water and Foam

Water and Foam fire extinguishers extinguish the fire by taking away the heat element of the fire triangle. Foam agents also separate the oxygen element from the other elements.

Carbon Dioxide

Carbon Dioxide fire extinguishers extinguish fire by taking away the oxygen element of the fire triangle and also be removing the heat with a very cold discharge.

What are the common causes of house fire accidents?

Rules of fighting fire

Only fight a fire if; The fire is small and contained, you are safe from toxic smoke, you have a

means of escape and your instincts tell you it's OK

How to use a fire extinguisher.

Fire extinguishers can be heavy, so it's a good idea to practice picking up and holding an extinguisher to get an idea of the weight and feel.

Take time to read the operating instructions and warnings found on the fire extinguisher label. Not all fire extinguishers look alike.

Practice releasing the discharge hose or horn and aiming it at the base of an imagined fire. Do not pull the pin or squeeze the lever. This will break the extinguisher seal and cause it to lose pressure.

When it is time to use the extinguisher on a fire, just remember PASS!

Pull the pin, and Aim the nozzle or hose at the base of the fire from the recommended safe distance.

Squeeze the operating lever to discharge the fire extinguishing agent.

Starting at the recommended distance, Sweep the nozzle or hose from side to side until the fire is out. Move forward or around the fire area as the fire diminishes. Watch the area in case of re-ignition

1. Electrical short circuit due to poor electrical wiring

2. Candles and fuel lamps being left unattended to, or left burning while asleep

3. Cooking equipment. People get destructed and leave their cooking unattended.

4. Careless smoking. Placing ash tray near anything combustible

5. Children playing with fire inside the house6. Short circuits from electrical appliances7. Light fire close to flammable substances e.g.

fuels, solvents, cleaning agents, and adhesive paints

1.4 what is Scientific inquiry.A scientific inquiry is a systematic (step by step) procedure of investigating (finding about) nature. It goes through six main stages, which are:

How do we make an observation?

.We make observations using the four senses, namely: sight, hearing, smelling and tactile feeling

by use of the hands.

Students’ task 2.8 (practical activity)

Grey iron fillings are mixed with sulphur powder on a white sheet of paper. The mixture is

transferred into a porcelain dish and heated.

a) What is the color of;

i) Iron fillings

ii) Sulphur powder

iii) Mixture of iron fillings and sulphur powder?

b) What is observed when the mixture is being heated and after heating?

c) What happens to the mixture of iron and sulphur on heating?

What is a hypothesis?

This is a suggested explanation to an observation. A hypothesis may be true or wrong, it has to

be experimented and tested.

A Theory

This is a scientific idea thought forwarded by somebody, communicated to other scientists, tested

and found to correctly explain an observation. A theory must be consistent with known facts.

A theory is built as a result of repeated experimental work to test a hypothesis, e.g. theories of

evolution, or origins of life.

(i) Observation (ii) Building a hypothesis(iii) Experimentation(iv) Building a theory(v) Theory testing(vi) The scientific law

Thermometer

Beaker

Molten Naphthalene

Heat

Clamp

The Scientific Law.

These are proven statements that are universal and consistent with observed behaviour of nature.

The scientific law predicts behavior of nature e.g. the law of gravitation force, the law of

electrolys

Determination of purity of substances

Whether in manufacturing, cooking or cleaning, substances are most efficient when they're

pure. Purity can be defined as the absence of any impurities

You can use numerous tests to check for purity, ranging from simple visual comparison to

sophisticated laboratory techniques.Techniques of determining purity

i) Visual techniques which involves looking for any other substance mixed with the

substance under test, for example, dirt/dust/foreign particles that may be suspended in

the liquid or settled at the bottom. This technique is very inaccurate. Why do you

think this technique is very inaccurate?

ii) Smell, can be used for non odoriferous substances that are non toxic. This technique

varies among individuals and limited to substances that are non toxic.

Accurate techniques include determination of;

i) Melting point

ii) Boiling point

iii) Density

iv) Refractive index

Task 2.7 (experimental)

Determining Melting and Boiling points

Experiment 3.11

a) AIM: To determine the melting point of Naphthalene.

Experiment 3.12: To determine the melting point of Naphthalene

Procedure:

Put about 2cm depth of Napthalein into a test tube and clamp it in a beaker, which is

half filled width glycerol & heat the glycerol on gauze supported on a tripod as shown

above

When naphthalene melts, insert the thermometer and continue heating the melt to rise

another 10 degrees. Lift the test tube out of the glycerol and wipe it clean.

Thermometer

Beaker

Ethanol

Heat

Retort stand

Water

Experiment 3.13

AIM:To determine the boiling point of Ethanol

Procedure:

Clamp the thermometer just above the surface of ethanol in a boiling tube immersed

in water.

Heat the water in the beaker and note the thermometer reading.

Procedure:

Put about 2cm depth of Napthalein into a test tube and clamp it in a beaker, which is

half filled width glycerol & heat the glycerol on gauze supported on a tripod as shown

above

When naphthalene melts, insert the thermometer and continue heating the melt to rise

another 10 degrees. Lift the test tube out of the glycerol and wipe it clean.

When the ethanol begins to boil and the thermometer reading is steady, record the

thermometer reading.

Boiling point of ethanol =………………………………….

Definition of terms:

Melting point:This is the constant temperature at which solid changes to a liquid.

The melting point of a substance is also the freezing point of that substance

when in liquid state.

Boiling point: This is the constant temperature at which the vapor pressure of a liquid equals to

the atmospheric pressure. Boiling is the process of formation of water bubbles at

the bottom of the container in which a liquid is placed and rapidly move to the

surface of the liquid.

Similarities between boiling and Evaporation:

(i) Both lead to the formation of a vapour

(ii) Both are affected by prevailing pressure.

Different Between Boiling and Evaporation

Boiling Evaporation

Occurs at a fixed temperature which varies

from one substance to another

Occurs over a wide range of temperature.

Boiling occurs throughout the bulk of the

liquid

Occurs only on the surface of the liquid

It is affected by impurities It is not affected by impurities.

N.B.: impurities may lower or elevate the boiling point of a liquid.

Vapor

This is a gaseous form of a substance which is normally a liquid or a solid at room temperature

and pressure.

Liquefaction of a gas

..0

Filter paperBlack dot at the center

Petri dish

This is the process of changing from a gas into a liquid. Liquefaction is normally done by

increasing pressure on the gas (compressing the gas) while lowering the temperature of the

compressed gas.

Separation of mixtures by chromatography Chromatography is a technique used to separate two or more components of a mixture by use of

a solvent over an absorbent medium.

The principle on which Chromatography works is that the different components of the mixture

spread at different rates as they are carried by the solvent front.

The term Chromatography was coined from the Greek word “chromos” which means colour.

In the earlier days Chromatography was used to separate only colored substances.

Today, Chromatography is used to separate a wide range of substances including the white and

colourless.

Examples of mixtures separated by Chromatography include: plant pigments e.g.

chlorophyll, dyes, proteins, fats, Blood Serum and other organic mixtures.

Student’s task 2.8 (practical investigation)

Aim: To separate Components of black Ink by use of Radial Paper Chromatography

Method:

A filter paper is placed on a clean dry tile.

By use of ballpoint pen, a black dot if ink is placed in the center of the filter paper.

The filter paper is then placed over the top of a petri dish.

By the use of a teat pipette a drop at a time of solvent is added to the very spot

containing the black dot. The drops are added at an interval of 15 seconds.

The solvent is allowed to spread out as far as possible: allow to dry.

Questions:

Retort stand

Absorbent paper

Pigment dot

Propanone solvent

(i) Name the colors that have spread out.

(ii) Draw a diagram to show the arrangement of the colours on the filter paper.

(iii) Identify the substance by color that spreads fastest.

(iv) Suggest one other mixture other than chlorophyll that can have its components separated by this method.

N.B.: The arrangement of colors (components) shown on the filter paper is called a

Chromatogram.

Vertical column Chromatography (Ascending Column Chromatography)This involves the use of an adsorbent medium (normally adsorbent paper) in a vertical position and partly immersed in the solvent. Column chromatography works on a much larger scale by packing the same materials into a vertical glass column. Experiment 4.13Aim: To separate components of chlorophyll pigment by use of vertical column paper ChromatographyMethod: Place some chopped beans (e.g. goat weed or lantana) in a mortar containing little sand. Cover the leaves with little propane and crush with a pestle to form a paste. Cut adsorbent paper (e.g. Filter) into a rectangular shape of about 10cm in length. Mark off a

point at 2cm from the bottom. Squeeze the paste to drop thick solution at exactly the marked point. Allow it to dry.

(Capillary tube may be used) Pour propane into a beaker to about 1cm height. Slowly insert the adsorbent paper in the beaker such that the pigment dot is above the surface

of propane Make the adsorbent paper vertically stand in propane by mounting it with a retort stand. Allow the solvent (propane) to ascend on the adsorbent paper until it is about 1 cm from the

top. Remove the paper and allow it to dry

Diagram:

Precaution: experiment should not be done under direct sunlight.

Questions:

(i) By the use of colour, identify the components of chlorophyll

(ii) Which component is likely to be in the greatest amounts?

(iii) Draw a well-labeled chromatogram formed.

Advantages of using Chromatography

(i) Can be used for both separation of the components of the mixture and identification

of the components in a mixture.

(ii) It requires very small samples for analysis

Application of Chromatography

(i) Identification of poison in blood serum (crime investigation)

(ii) Determination of purity of substances e.g. fats, proteins or food coloring.

(iii) Identification of components of plant pigments (biochemistry or molecular biology)

(iv) Determination of the content of alcohol in blood (traffic police in breath analyzer)

(v) Identification of drugs in blood for sportsmen and women (Dope test)

Student’s task 2.9

Introduction

You have been elected a member of the village youth committee in your home area. On this

committee you are in charge of health, environment and natural resources. The you youth

committee is in preparation to receive visitors from the Lottery club of lindberg-Mexico.

Task

You are require to give a report on level of contamination of the water resources in your village located as follows

i) Borehole water in the trading centerii) Spring well in the valleyiii) Open well behind the local leather industry

For each water source describe the different tests of purity would carry out to test the purity of water.