DCHS SW 1

West Lothian Council

HydrocarbonsReadFossil fuels like coal, oil and natural gas contain a mixture of chemicals. The main chemicals in these fossil fuels are called hydrocarbons. A hydrocarbon is a compound made from only hydrogen and carbon atoms joined together.

You already know that burning is a chemical reaction. This means that at least one new substance must be made.

Watch your teacher demonstrate what happens when a candle is burned. Candles are made from oil so they contain hydrocarbons. This apparatus will let us see what new substances are made when hydrocarbons are burned in air.

The following things happened:

A colourless liquid collected in the first test tube. This liquid was heated and was found to boil at 100C.

The limewater turned cloudy. This tells us that carbon dioxide gas was also made when the candle burned.

Write a heading and do the work below.1. The main chemicals in fossil fuels are called H__________________.

DCHS SW 2

burning candle (hydrocarbon)

ice/salt bath

limewater

suction pump

2. a) Complete the table below by looking at the models around the classroom . Remember the atoms are colour-coded: white = hydrogen; black = carbon; red = oxygen; blue = nitrogen; green = chlorine; yellow = sulphur.

b) The molecules which are hydrocarbons are __________________.3. In the test tube in the ice bath I seen ___________ forming.4. The limewater in the last test tube turned _____________.5. Copy and complete the following sentences.

6.R

emember when a hydrocarbon burns it reacts with oxygen to make new substances. Copy and complete the word equation for the reaction of a hydrocarbon burning.

hydrocarbon + __________ _________ + ___________ ___________

Burning hydrocarbons in a poor supply of airReadWhen the hole of a bunsen burner is open, the methane burns completely because there is plenty of air available. This is called complete combustion. However when the hole is closed, the methane gas burns in a low supply of air. This means that the hydrocarbon does not burn completely. This is called incomplete combustion. When the amount of air for burning is low, the new substances that are made in the burning reaction are different.

Write a heading and do the work below.

DCHS SW 3

When a hydrocarbon is burned in air the two new substances that are made are w_________ and c___________ d___________ gas.

model formulaABCDE

1. The type of combustion which happens when there is plenty air is called _______________________________________________.

2. The type of combustion which happens when the amount of air is low is called _______________________________________________.

3. Collect a bunsen burner, heat mat, white tile and tongs and do the experiment shown below.

a) After I had held the white tile beside the blue flame I noticed _________________________________________________________________. b) I noted _____________________ had formed on the tile after I held it

beside the orange flame.c) The flame which was the sootiest is the blue/orange flame.

4. Collect the information sheet about pollution from fossil fuels and answer the questions below.a) The names of the two substances that are made when a hydrocarbon

burns in a low supply of oxygen are ______________ and ___________ _________________.

b) Carbon monoxide is a dangerous gas because _________________________________________________________________________

c) The name of the poisonous gas which is made when fuels containing sulphur are burned is called _____________ ______________.

d) The name of the gas which is made when nitrogen and oxygen react in a car engine is _____________ _______________.

e) The names of two gases that can cause acid rain are ___________ ____________ and _______________ _________________.

f) Lead causes pollution because _______________________________________________________________________________________.g) You be exposed to benzene fumes _____________________and

they are dangerous because ______________________________

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Hold the tile beside the blue flame for 1 to 2 minutes. Then repeat the experiment but this time with the orange flame.

_______________________________________________________h) List two ways that pollution from cars can be reduced.

____________________________________________________________________________________________________________

Look at the sheet called “More pollution problems” about carbon monoxide poisoning. You may have time to design a poster to warn people of the dangers of carbon monoxide.

Separating liquidsReadTo separate a mixture of liquids we use a process called distillation. You may have seen some distillation in S1 and S2 science.

To separate liquids by distillation we need two steps:

1. The mixture is heated until the first liquid boils and turns into a gas.

2. The gas that is made is then cooled down again and turns back into a liquid again.

Watch your teacher carry out the distillation demonstration 2.43. You may also be shown another demonstration involving coloured water.

The liquid in the boiling tube is a mixture of alcohol and water.

Alcohol will boil at 79C and water will boil at 100C.

The mixture is heated up to 79C. This means that the alcohol will boil and turn to a gas but the water will stay as a liquid. The alcohol gas will move along the tube and when it cools it turns to a liquid and can be collected.

DCHS SW 5

heat

alcohol and water mixture alcohol

Write a heading and do the work below.1. The name of the process that is used to separate a mixture of liquids is

_____________________.2. The two steps which need to happen in distillation are _________________________________________________________________________.3. Look at the diagram of the alcohol experiment and label the diagram

with the following two labels:

4. Copy and complete the following sentences.

Separating crude oil into fractions

Crude oil is oil that comes straight from the ground. It contains a mixture of different hydrocarbons. The crude oil can be separated into useful hydrocarbons using fractional distillation because the hydrocarbons have different boiling points. The different substances that are made after the crude oil has been separated are called fractions.

The process can be carried out in the laboratory on a small scale.

DCHS SW 6

This means that we have separated the mixture because the liquids have different boiling points.

liquid turns into a gas here gas turns into a liquid here

Fractional distillation is used to separate l_____________. It works because the liquids have different b__________ p__________.

heat

crude oil

fraction

Your teacher may show you a demonstration of the fractional distillation of crude oil.

The crude oil is heated until the first fraction boils and turns into a gas. This gas goes along the tube, cools down and turns back into a liquid that can be collected.

After the first fraction is collected the oil is heated to a higher temperature and the second fraction collected.

This is repeated until all the different fractions have been collected.

Write a heading and do the work below.1. The kind of chemicals which are found in crude oil are ____________.2. The name of the process that is used to separate crude oil is _________

_________________________________________________________3. This process works because

___________________________________ _________________________________________________________

4. The liquids are called ___________________ after they are separated.5. Look at the fractional distillation diagram and describe what is done to

separate the crude oil. ____________________________________________________________________________________________________________________________________________________________________________________

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Each fraction contains a group of hydrocarbons that have similar boiling points.

Using fractionsReadThe fractions that are made from crude oil have been given names and have many uses. eg

The fraction that is called petroleum gas is used as a fuel for cooking and central heating

The fraction that is called petrol is used as a fuel for cars

The fraction called diesel is used as a fuel for trains, buses and lorries

The fraction called kerosine is used as fuel for aircraft.

Lubricating oil is the name of a fraction that can be used to make candles.

Bitumen is a fraction that is used to make tar for building roads.

6. Copy the sentence below.

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Most of the fractions that are made from crude oil are used as fuels.

7. Complete the table below to show the names of some of the fractions from crude oil and what they are used for (you can choose whether to write in the use or draw a picture to illustrate the use).

Fractional distillation in industryReadIn Britain, 250,000 tonnes of crude oil are separated into fractions every day. This is done on a large scale in a large structure called a fractionating tower. You might have seen these if you have been in Grangemouth. The fractions are piped away from the tower at different heights depending on their boiling points.

Write a heading and try the work below.1. The building where crude oil is separated in industry is called _______

_______________.2. The height of the pipes depends on _____________________________

_________________________________________________________.3. Collect a copy of the sheet called “fractional distillation in industry”

and stick it into your jotter.

DCHS SW 9

name of fraction use (picture or words)petroleum gas

petrol

diesel

kerosine

lubricating oil

bitumen

4. The smallest molecules come out at the top/bottom of the fractionating tower.

5. The largest molecules come out at the top/bottom of the fractionating tower?

More about the molecules in crude oil

You should already know that the molecules in crude oil can be separated by fractional distillation because they have different boiling points but this is not the only difference. The molecules in the fractions are different sizes. We can get an idea of how big the molecules are by counting the number of carbon atoms that are in each molecule.

Write a heading and do the work below.1. Look at the display of models on the wall that shows the types of

molecules that we can get from crude oil.

a) Make three lists beside each other with the headings “name of the fraction”, “number of carbon atoms” and “boiling point” (clue: carbon atoms are black)

b) Now turn your three lists into a table by drawing lines with a ruler.

2. What is the name of the fraction that has the smallest molecules?3. What is the name of the fraction that has the largest molecules?4. Copy and complete the sentence below.

5. Use the table below to help you answera) What fraction would have 17 carbon atoms in the molecules?b) What fraction would have a boiling point of –10C?c) What can you say about the size of the molecules in diesel compared to

the size of the molecules in petrol?

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name of fraction Number of carbon atoms in the molecules

Boiling point C

petroleum gas 1 to 4 below 20petrol 5 to 9 about 70kerosine 10 to 16 about 130diesel 15 to 20 about 250lubricating oil more than 20 about 350bitumen more than 40 about 400

The bigger the molecules the ____________ the boiling point.

What other properties are different?

Apart from the size and the boiling point, the fractions from crude oil also have other differences.

They are different in colour.They are different in how runny they are.They are different in how easily they can evaporate.They are different in how easily they catch fire.

In chemistry we use scientific words to describe different properties.

Viscosity means how runny a substance is. The more viscous the thicker and less runny (syrup is more viscous than water).

Flammability means how easily it catches fire. The more flammable the easier it catches fire.

Write a heading and do the work below.1. What four other properties can be different about the fractions from

crude oil?2. What does viscosity mean?3. What liquid is more viscous between water and syrup?4. What does flammability mean?5. Copy the table below and complete the colour column by looking at the

display of crude oil fractions.

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name of fraction

Number of carbon atoms in the molecules

colour viscos-ity

evaporati-on

flammability

petroleum gas 1 to 4 not viscous

easy to evaporate

burns easily

petrol 5 to 9kerosine 10 to 16diesel 15 to 20lubricating oil more than 20bitumen more than 40 very

viscoushard to evaporate

hard to burn

6. Now copy and complete the sentences below choosing the correct word.

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The bigger the molecules the lighter/darker the colour.The bigger the molecules the more/less viscous.The bigger the molecules the harder/ easier to evaporate.The bigger the molecules the harder/easier to burn

Supply and demand The amount of each of the fractions we can get from crude oil is called the supply. The amount of each of the fractions that the world needs is called the demand. Crude oil contains much more of the larger molecules than smaller ones. This means that the amount of the smaller molecules we can get from crude oil is not always enough to match how much the world needs. This means that supply does not meet demand.

Write a heading and try the work below.1. What does supply mean?2. What does demand mean?3. Which type of molecules is there more of in crude oil. 4. Why does supply not meet demand?

Look at the graph below to answer the next set of questions.

5. For which two fractions is the supply much less than the demand?

6. Suggest a reason for the high demand for these fractions.

7. Which two fractions do we have too much of?

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Gas Petrol Kerosene Diesel Bitumen

supply

demand

CrackingTo solve the problem of supply not meeting demand, scientists have found a way to change the larger molecules into smaller ones. The way they do this is in a reaction called cracking. (like cracking an egg into smaller pieces, the large molecules are broken up into smaller, more useful molecules).

Your teacher may demonstrate how to do a cracking reaction in the lab.

Write a heading and do the work below.1. What is the reaction called that lets us break up large molecules into

smaller ones to make sure that supply meets demand.2. Copy the diagram of the cracking experiment.3. Look at the drawing of a molecule below.

This molecule is a hydrocarbon because it only contains hydrogen and carbon. It is called duodecane and has the molecular formula C12H26 (remember to work out a formula all we need to do is count the atoms).

Draw the molecule and beside it write its formula.

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indicator solution

aluminium oxide on mineral wool

thin plug of mineral wool

mineral wool soaked in paraffin

HEAT

4. Collect a model kit and build the duodecane molecule (carbon atoms are black and hydrogen ones are white).

Now break up your model to make two smaller molecules but you need to make sure that there are no empty holes left. You might need to use the bendy bonds.

Draw the two molecules you have made when you cracked the duodecane and write the formula beside each one.

5. Copy and complete the equation below for the molecule that you made:

C12H26 ________ + _________

DCHS SW 15