YEAR 11

Combined Chemistry – Booklet

2Lesson Recall Knowledge

Check1. Hydrocarbons and Fractional Distillation /8 /82. Products and Trends of Fractional Distillation /8 /83. Cracking and Testing Alkanes and Alkenes /8 /84. Purity, Formulations and Identification of Gases /8 /85. Chromatography /8 /86. Chromatography Practical /8 /8

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Name: ____________________________________________

Teacher: __________________________________________

Class: _____________________________________________

Chemistry Knowledge Web

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Overview of the topics and skills taught over Year 11

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Knowledge

Biology

Inheritance, Variation and Evolution

Ecology

Chemistry

The Rate and Extent of Chemical Change

Organic Chemistry

Chemical Analysis

Physics

Waves

Magnetism and Electromagnetism

Space (Separate Science Only)

Key Skills

Using laboratory equipment safely

Practical skills using scientific equipment

Making and recording observations

Using models to understand concepts

Using key vocabulary

Topic Big Statement

The aim of the topics taught in this booklet is to explain how useful products can be obtained from crude oil and to understand how different techniques can be used to separate mixtures and identify the chemicals that they are made of.

Where the Unit Fits in the Sequence

These are the final topics you will learn in chemistry, as they build on all of the ideas you have learned so far and require you to use the skills that you have acquired.

The target 9 activities in this booklet will extend your knowledge.

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Threshold Concepts

By the end of the unit you should be able to: R A G

State the general formula of alkanes.

Describe the process of fractional distillation.

Identify alkanes and alkenes using bromine water.

Explain how mixtures are separated by chromatography.

Calculate Rf values.

Use simple tests to identify common gases.

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Relevant core questions, linked to this unit:

Core Question: Answer:Define the term hydrocarbon.

Hydrocarbons are compounds that contain hydrogen and carbon only.

Name the process used to separate crude oil.

Fractional distillation.

Describe how the flammability of hydrocarbons changes as the length of hydrocarbon increases.

As hydrocarbons get longer, their flammability decreases.

Describe the products of cracking.

During cracking, long alkanes are split into a shorter alkane and alkene.

Explain why pencil is used to draw the start line on a chromatogram.

Pencil does not dissolve in the solvent and therefore it will not affect the results.

Describe the test for hydrogen gas.

There is a squeaky pop sound when you insert a burning splint into a tube of the gas.

Describe the test for carbon dioxide

When carbon dioxide is bubbled through limewater, the limewater changes from clear and colourless to cloudy and milky.

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Knowledge OrganiserThe keywords for this topic will appear in this order:

Word Meaning

crude oil A fossil fuel, in the liquid state, formed from the remains of microscopic dead plants and animals that lived in the sea.

fractional distillation

A method of separating a mixture of liquids with different boiling points into individual components (fractions).

viscosity How thick or runny a liquid is. Low viscosity is very runny, high viscosity is thick.

alkane A hydrocarbon in which all the bonds between the carbon atoms are single bonds.

general formula A type of formula that represents the composition of any member of an homologous series.

alkene A hydrocarbon in which there are one or more double bonds between carbon atoms.

cracking A chemical reaction in which large alkane molecules are split into two or more smaller alkanes and alkenes.

chromatography A technique for separating the components of a mixture – for example different food colouring agents.

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Tier 3 Vocabulary

Word Meaning In a sentence

crude oil A fossil fuel, in the liquid state, formed from the remains of microscopic dead plants and animals that lived in the sea.

Crude oil is a mixture of hydrocarbons.

hydrocarbon A compound containing hydrogen and carbon only.

Hydrocarbons are found in crude oil.

fraction A component of a mixture that has been separated by fractional distillation.

The different hydrocarbons in crude oil are called fractions.

fractional distillation

A method of separating a mixture of liquids with different boiling points into individual components (fractions).

Fractional distillation is used to separate the different fractions in crude oil.

viscosity How thick or runny a liquid is. Low viscosity is very runny, high viscosity is thick.

Higher viscosity hydrocarbon have higher boiling points.

alkane A hydrocarbon in which all the bonds between the carbon atoms are single bonds.

Alkanes are saturated hydrocarbons.

general formula A type of formula that represents the composition of any member of an homologous series.

The general formula for an alkane is CnH2n+2.

alkene A hydrocarbon in which there are one or more double bonds between carbon atoms.

Alkenes are unsaturated hydrocarbons.

cracking A chemical reaction in which large alkane molecules are split into two or more smaller alkanes and alkenes.

Cracking turns large alkanes into shorter, more useful alkanes and alkenes.

saturated A molecule that contains only single bonds between the carbon atoms in a chain.

Saturated hydrocarbons only contain single bonds.

unsaturated A molecule that contains one or more Unsaturated hydrocarbons 8

Word Meaning In a sentence

double bonds between carbon atoms in a chain.

contain one or more double bonds.

homologous series

A family of compounds that have the same general formula and similar properties, but have different numbers of carbon atoms.

Compounds in a homologous series have the same general formula.

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Baseline Assessment

1 What happens in all chemical changes?

a A gas is produced.

b Heat energy is given out.

c Elements change into a compound.

d One or more new substances are formed.

2 A compound contains:

a only one type of atom.

b only one element.

c only two elements joined together.

d at least two elements joined together.

3 Which of the following always happens during a chemical reaction?a Compounds react and split up into free

atoms.b Elements join together to make new

elements.c Atoms are broken down into smaller

particles.d The atoms in the reactants are rearranged

to make the products.

4 This chromatogram was made using black ink. How many different coloured inks were in the mixture?

a 4 b 6

c 5 d 7

5 What is chromatography used for?

a to separate a solid from a liquid

b to separate out dissolved solids

c to separate a liquid from a solution

d to separate a mixture of liquids

6 Why do the substances separate in a chromatogram?

a The solvent dissolves the substances and carries them up the paper.

b Some of the substances evaporate before the others.

c The solvent carries the substances at different speeds.

d The solvent evaporates at different points up the chromatogram.

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7 In this chromatography experiment, why are the sample points placed above the water line?

a so that the samples don’t dissolve in the water at the bottom

b so that the pencil line dissolves as the water moves up the paper

c so that the samples evaporate

d so that the samples mix together

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Lesson 1 – Hydrocarbons and Fractional DistillationRecall

1. Name three non-metal elements.

2. Describe what is meant by a mixture.

3. Define the term ‘boiling point’.

4. Explain why the hydrocarbons in crude oil have different boiling points

5. Describe what distillation is used for.

6. Define the term fuel.

7. Describe what happens to electrons during the formation of a covalent bond.8. Name the elements found in methane (CH4).

Crude oil

Crude oil is a finite resource found in rocks. Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud. Crude oil is a mixture of a very large number of compounds.

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https://www.youtube.com/watch?v=8YHsxXEVB1M

Task - during the video either make notes or jot down some key / tier 3 vocabulary that you hear.

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Task – now use your notes to answer the following questions. Your aim is to complete ALL levels and pick up as many points as you can.

My answers-

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Hydrocarbons

Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only. Here are a selection of hydrocarbon structure diagrams:

Most of the hydrocarbons in crude oil are called alkanes.

An alkane is a type of hydrocarbon where the carbon and hydrogen are all joined by SINGLE covalent bonds. This is indicated in structure diagrams by a single straight line, see below:

The general formula for the homologous series of alkanes is CnH2n+2.

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A single covalent bond – this means there is one shared pair of electrons between the atoms on either end of the line

Tier 3 language - homologous series

This simply refers to a chemical family, or a group of compounds that share a common structure and therefore certain properties.

The general formula means that for every one carbon atom to work out the number of hydrogen atoms in that formula you simply multiply that number by 2 and then add 2.

Task - Look at this worked example and then fill in the missing formulae

Name of alkane and number of carbon atoms

Working out Formula

Methane (1) Carbon = 1Hydrogen = 1 x 2 = 22+2 = 4

CH4

Ethane (2)

Propane (3)

Butane (4)

The first four members of the alkanes are methane, ethane, propane and butane.

When naming alkanes be aware that the prefix links to the number of carbons in the hydrocarbon - meth=1, eth=2, prop=3 and but =4. The suffix indicates what kind of hydrocarbon it is, ane = alkane and ene=alkene (more about these in another lesson).

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Fractional distillation

As we have mentioned, crude oil is a mixture of a very large number of compounds. In order to get the most out of each part of the mixture, the substances must be separated and purified. The process used to separate the different compounds in crude oil is called fractional distillation. Each of the fractions share a similar number of carbons and boiling point.

Look at this image of the process of fractional distillation:

A tall fractionating column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.

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Knowledge Check

1. Define the term ‘finite resource’.

2. Name the substances found in crude oil.

3. Define the term ‘hydrocarbon’.

4. State what is represented by each line on this diagram.

5. Explain why a general formula is useful.

6. State the purpose of fractional distillation.7. Explain what chemicals have in common at each level in the fractioning column. 8. Describe a property of molecules found at the top of the fractionating column.

Target 9 extension task: [check answers in appendix]

(a)     Methane is burned in a plentiful supply of oxygen.

Which is the correct balanced chemical equation?

Tick one box. 

CH4 + O2 → CO2 + H2O

CH4 + 2O2 → CO2 + H2O

CH4 + 2O2 → CO2 + 2H2O

CH4 + 3O2 → 2CO2 + 2H2O

(1)

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(b)     Burning fuels causes atmospheric pollution.

Write one effect for each pollutant in Table 1. 

Table 1

Pollutant Effect

Carbon monoxide  

Sulfur dioxide  

Particulates  

(3)

(c)     Methane, petrol and coal are fuels.

Table 2 shows information about these fuels. 

Table 2

Fuel State Energy content in kJ per g

Mass in mg of CO2

produced for one kJ of energy released

Methane Gas 52 53

Petrol Liquid 43 71

Coal Solid 24 93

Evaluate the use of the fuels.

Use in the information in Table 2 and your knowledge.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (6)

Lesson 2 – Products of Fractional DistillationRecall

1. Describe how crude oil is formed.

2. Name the process that separates the substances in crude oil.

3-5. Draw a diagram of a solid, liquid and gas.

6. Describe some differences between liquids and gases.

7. Describe what happens during a displacement reaction.

8. Describe how ions are formed.

In our last lesson we considered the important natural material called crude oil. We learnt that it is a complex mixture of hydrocarbons. We now know that a process called fractional distillation can be used to separate the different compounds found in this mixture. This process uses the different boiling points of the fractions to separate them through heating, evaporation and condensing of the chemicals.

The reason scientists go to the trouble of separating the mixture is because the products are so useful. The fractions can be processed to produce fuels and feedstock for the petrochemical industry. Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil. Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergents.

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Sequencing Task

Put the steps of fractional distillation in the correct order.

The vaporised crude oil enters the fractionating column, which is hottest at the bottom.The vapours condense when they become cool enough.

The shortest hydrocarbons leave the fractionating column at the top.

Vapours from the oil rise through the column.

The different fractions (in liquid form) are led out of the column at different heights.Crude oil is heated until it evaporates.

Watch the attached video with your teacher and make any notes you think would be useful to revise from: https://www.youtube.com/watch?v=PYMWUz7TC3A

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Extended writing challenge: Hydrocarbons

Describe and explain how the different hydrocarbons are separated from the mixture in crude oil.

Use the diagram to help you with your answer.

Properties of the fractions:

You have been previously told that different chemicals have different properties and that these properties fall into two main categories. Those categories where chemical and physical properties. Chemical properties cover the way the chemical reacts with others and the reasons for this relating to electron configuration. The physical properties were all the other traits that chemical has such as colour, boiling point, and viscosity.

Here we will consider how the structure of the chemical from the fractioning column links the properties it has. We need to recall that the smallest carbon chain hydrocarbons are found to condense and collect at the top of the column and the largest at the bottom.

As we can see from the image here, the size of the carbon chain impacts the chemical’s following physical properties: boiling point, viscosity and flammability. But what does that mean? Take a look at the definitions below –

Boiling point – the temperature at which a substance changes from a liquid to a gas

Viscosity – the ease with which a substance flows (how runny is it, very viscous means not runny)

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(6 marks)

Flammability- the ease with which something ignites or combusts

1. Where in the fractionating column do you find hydrocarbons with the highest viscosity?

____________________________________________

2. Where in the column do you find hydrocarbons with the highest flammability?

____________________________________________

3. Where in the column do you find hydrocarbons with the highest boiling point?

____________________________________________

4. Where in the column do you find hydrocarbons with the longest hydrocarbon chains?

____________________________________________

You need to remember your chemistry of combustion from Year 8 - The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water, like in this equation –

Knowledge Check

1-2. Give 2 examples of physical properties chemicals have3. Define the word viscosity

4. Describe how viscosity changes as you move up the fractionating column.5. Describe how the flammability of the chemical changes as you move up the fractioning column 6. Describe how carbon chain length affects the boiling point a substance has7. Explain why people burn fuels.

8. Explain why both the carbon and

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hydrogen are said to be oxidised during the combustion of a hydrocarbon fuel.

Target 9 extension task: [check answers in appendix]

The table shows some information about alkanes. 

Name Formula Relative formula mass Boiling point in °C

methane CH4 16 –160

ethane C2H6 30 –90

propane   44 –40

butane C4H10 58  

pentane C5H12 72 36

hexane C6H14 86 68

          (a)     Give the formula of propane.

___________________________________________________________________(1)

          (b)     (i)      What happens to the boiling points of the alkanes as the relative formula mass increases?

______________________________________________________________(1)

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(ii)     Draw a graph. Plot the points and draw a best fit line.

 (3)

(iii)     What is the boiling point of butane?

______________________________________________________________(1)

(iv)    Show clearly on the graph how you found the boiling point of butane.(1)

(c)     Circle which of the following is not an alkane.

          C71116                C9H18                C11H24                  C24H50

(1)(Total 8 marks)

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Lesson 3 – Cracking and Testing Alkanes and AlkenesRecall

1. Describe the effect of increasing temperature on the rate of a reaction.2. Define the term “reversible reaction”.

3. Give the pH of a strong alkali.

4. Complete the equation: Lithium oxide + sulfuric acid

5. State which part of the fractionating column is the hottest.6. Define the term “hydrocarbon”.

7. Give the name for a positive ion and the name of the electrode it is attracted to.8. Draw the electron configuration of chlorine and sodium, show the electron transfer with an arrow and then draw the ions produced.

Alkanes vs Alkenes

So far, we have learned about hydrocarbons called alkanes. They have a general formula of CnH2n+2, they only contain single bonds and each carbon atom is bonded to as many other atoms as possible, which is why we refer to them as saturated hydrocarbons.

This is butane.

You can tell that the bonds are all single in butane because they are all single lines.

Alkenes are hydrocarbons that contain a double bond. This makes them more reactive than alkanes.

This is butene.

The double bond is shown as a double line. There is only one double bond in alkenes.

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Because alkenes contain a double bond, each carbon is not bonded to the maximum number of other atoms, so alkenes are referred to as unsaturated hydrocarbons.

Polymers and Chemical Production

Ethene is the shortest alkene. It is also one of the most useful because it is used to make the plastic polythene, which is used to make plastic bags and plastic bottles. In order to make polythene, the double bond in the ethene is broken and then they are joined together – this process is called polymerisation and polythene is an example of a polymer.

Several shorter alkenes are also the starting materials for the production of many chemicals.

Keyword Comprehension Task

1. Which type of hydrocarbon is saturated?

____________________________

2. Which type of hydrocarbon contains a double bond?

____________________________

3. How can you tell from a diagram that there is a double bond?

_____________________________________________________________________________

_____________________________________________________________________________

4. Which alkene is the shortest?

____________________________

5. What is the name for the substance produced when alkenes are joined together?

____________________________

Cover Write Check Task

These are the key facts that you need to know about alkanes and alkenes. Learn them off by heart, cover write check them on the next page and then answer the questions.

AlkanesContains only single bonds

Saturated

AlkenesContains a double bond

Unsaturated29

Alkanes Alkenes

Alkanes Alkenes

Alkanes Alkenes

Mini Test

1. Which hydrocarbon has only single bonds?

_____________________

2. Which hydrocarbon is unsaturated?

_____________________

3. Which bonds are found in alkenes?

_____________________

4. Which hydrocarbon is saturated?

_____________________

5. Which bonds are found in alkanes?

_____________________

6. Which adjective would be used to describe an alkene?

_____________________

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Testing for Alkenes

Misconception Warning!Do not mix up colourless and clear: they have different meanings.

Colourless is when a substance has no colour. Clear is when a substance is transparent.

This is a red, but clear liquid.

We can use bromine water to distinguish between alkanes and alkenes. Bromine water is orange. If an alkane is added to bromine water, it stays orange. If an alkene is added to bromine water, it will change to colourless.

Addition of Bromine Water:

Practical Activity

Use bromine water to distinguish between an alkane and an alkene.

Observations:

_____________________________________________________________________________

_____________________________________________________________________________

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_____________________________________________________________________________

Cracking

The fractional distillation of crude oil produces alkanes that are different lengths. The shorter alkanes are in high demand because they are used as fuels, but the longer alkanes are not in very high demand and therefore there is a large surplus (left over amount) of long alkanes.

To produce more short alkanes, for fuels, and alkenes, to make polymers, we can crack the long alkane chains. This process is called cracking.

Cracking is an example of thermal decomposition. This is when you heat up a substance to get it to break into smaller parts.

There are two methods of cracking:

Catalytic Cracking: heat the alkanes to vaporise them and then pass them over a hot catalyst.

Steam Cracking: heat the alkanes to vaporise them, mix them with steam and then heat them to very high temperatures.

Balancing Equations

Because cracking is a chemical reaction, there will be the same number of carbon and hydrogen atoms in the reactants and products.

The equations for these reactions should be balanced in the same way as any other reaction (by adding big numbers in front of the chemicals).

Worked Example (to go through with your teacher):

C14H30 ------> C6H14 + C4H8

C = C =

H = H =32

Balancing Equations Task

1. C18H38 ------> C12H26 + C3H6

C = C =

H = H =

2. C20H42 ------> C12H26 + C2H6

C = C =

H = H =

3. C18H38 ------> C10H22 + C4H8 + C2H4

C = C =

H = H =

4. C25H52 ------> C11H24 + C4H8 + C3H6

C = C =

H = H =

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Knowledge Check

1. Give the name of the hydrocarbon that contains a double bond.2-4. Describe the test to see if a hydrocarbon is an alkene or alkane and how you would interpret the results.

Test:

Result for alkane:

Result for alkene:

5. Name the substance produced when alkenes are joined together.6. Define the term “cracking”.

7. Name the two types of cracking.

8. Balance this equation: C25H52 ------> C13H28 + C4H8

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Target 9 extension task: [check answers in appendix]

Q3.

(a) The table shows information about two alkenes.They are named in the same pattern as alkanes.      Complete the table to show the names and structures of these alkenes.

(2)

 (b) (i) Ethene is an unsaturated compound.           State what is meant by unsaturated.

(1)      ..............................................................................................................................................(ii) Describe what is seen when ethene is passed into bromine water.

(2)      ..............................................................................................................................................      ..............................................................................................................................................      ..............................................................................................................................................

 (c) Alkenes can be obtained by cracking some fractions obtained from crude oil.   Explain what is meant by cracking.

(2)      ..............................................................................................................................................      ..............................................................................................................................................      ..............................................................................................................................................

 (d) (i) Complete the sentence by putting a cross ( ) in the box next to your answer.            Molecules of ethene are reacted together to form poly(ethene).            The reaction taking place is

(1)    A   combustion    B   photosynthesis    C   decomposition    D   polymerisation

(ii) Poly(ethene) is used to make plastic carrier bags.      Many of these bags are put into landfill sites.

Explain why the presence of waste plastic in landfill sites causes problems.(2)

      ..............................................................................................................................................      ..............................................................................................................................................      ..............................................................................................................................................      ..............................................................................................................................................

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      ..............................................................................................................................................(Total for Question = 10 marks)

Lesson 4 – Purity, Formulations and Identification of GasesRecall

1. State the group of the periodic table that contains the alkali metals.2. Describe the arrangement and movement of particles in a liquid.

3-7. Sand and salt are stirred in water and then filtered. Complete the 5 labels in the diagram.

8. Which method would be used to extract a very reactive metal, like sodium?

Pure Substances vs Mixtures

A pure substance is a single element or compound, so we could have pure oxygen (an element) or pure water (a compound).

Mixtures contain more than one substance and could contain elements and/or compounds, for example, orange juice is a mixture of water, citric acid, vitamin C, glucose and other substances.

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A scientist would not consider this orange juice to be pure.

The melting point of a substance is the temperature where it changes from a solid to a liquid as it is heated. As freezing is just the opposite of melting, a substance would also freeze at this temperature and change from a liquid into a solid as it is cooled. The boiling point of a substance the temperature where it boils and the substance rapidly changes from a liquid into a gas.

Tier 3 Vocab Task

Use the information above, to write a definition for each term.

Tier 3 Vocab DefinitionPure

Mixture

Melting Point

Boiling Point

Pure substances melt and boil at specific temperatures. For example, pure water melts at 0⁰C and boils at 100⁰C. During a state change, the substance stays at this temperature – so boiling water stays at 100⁰C – it will only exceed this temperature when all of the water has turned into steam.

Mixtures, however, change state over a range of temperatures. We use this knowledge a lot in everyday life: for example, salt water (a mixture) freezes between – 5 and – 10⁰C, which is why the salt in grit stops roads from freezing in winter.

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Look at the freezing point on these graphs and work out which graph shows a pure substance and how you can tell?

_______________________________

_______________________________

_______________________________

A B

Formulation

A formulation is a mixture that has been designed as a useful product. Several substances are mixed together in very carefully measured quantities to make sure that the product has the properties that you want.

Eg. Calpol is a mixture of paracetamol (to relieve pain), malitol (to make it sweeter) and some solvents for these substances to dissolve in, so that it is a liquid medicine and therefore suitable for children.

Imagine you have been asked to design a metal alloy for aeroplane wings. What properties do you think your formulation would need?

_____________________________________________________________________________

_____________________________________________________________________________

What could happen if you chose the wrong metals, in the wrong quantities, for your formulation?

_____________________________________________________________________________

_____________________________________________________________________________

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Identifying Gases

Over the course of your GCSE so far, you have learned about many experiments that produce a gas during the reaction. Most of these gases are odourless and colourless, it is therefore important to understand the scientific tests that can be used to identify which gas has been produced.

Do the following tests and describe the results.

Gas Test Picture of Experiment Result Oxygen (O2) Insert a glowing

splint into a tube of the gas.

Hydrogen (H2) Insert a lit (burning) splint into a tube of the gas.

Carbon Dioxide (CO2) Bubble the gas through limewater (calcium hydroxide solution).

Chlorine (Cl2) Insert damp blue or red litmus into the gas.

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Knowledge Check

1. Define the term “pure”.

2. Describe how boiling points are different in pure substances and mixtures.3. Give the melting and boiling point of water.

MP =BP =

4. Explain why alloys are considered to be formulations, not simple mixtures.5. Describe the test for oxygen.

6. Name the gas that produces a squeaky pop when tested using a lit splint.7. Describe the test for chlorine.

8. Name the chemical used in the test for carbon dioxide.

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Target 9 extension task: [check answers in appendix]

Understanding Melting Points

1. At 20⁰C, would the element be a solid, liquid or gas?

HINT: If the temperature is higher than the melting point, the substance would be a liquid. If the temperature is higher than the boiling point, the substance would be a gas.

Fluorine –

Chlorine –

Bromine –

Iodine –

Astatine –

2. The boiling point of water is 100⁰C.

The boiling point of salt is 801⁰C.

If I had some salt water, what temperature would it boil at? ___________________

____________________________________________________________________

When you have a ___________ of substances, they melt and boil over a _______ of temperatures. _______ substances have a ___________ boiling point.

range / pure / mixture / specific

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Lesson 5 – ChromatographyRecall

1. Define the term “hydrocarbon”.

2. Explain why graphite can conduct electricity but diamond can’t.

3. Complete the half equation: Al3+ + e– Al

4. Calculate the number of neutrons in an argon atom – its mass number is 40 and its atomic number is 18.5 – 6. Name the products when sodium and water react together.

Sodium + water ________________ + _____________

7. Define the term “pure”.

8. Describe the colour change when carbon dioxide is bubbled through limewater.

Chromatography Required Practical

You have completed this practical in year 7 and year 9, but we are now going to look into the experiment in more detail and interpret the results more thoroughly.

Paper chromatography is a technique used to separate mixtures of soluble substances. It is particularly important for scientists testing food colourings, inks and dyes to see if they are safe.

Watch the video and put the steps of the chromatography practical in order:

https://www.youtube.com/watch?v=pnTGNAfu6GE

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Allow the solvent (water) to move through the paper, but remove the chromatogram before the solvent reaches the top.Add small spots of ink/dye to the pencil line on the paper.

Measure the distance travelled by the solvent and by the different dyes in each spot.

Place the paper into the container with a very small amount of the solvent in the bottom. Make sure the pencil line and spots are above the level of the solvent.Allow the chromatogram to dry.

Draw a pencil line across the chromatography paper, 1-2cm from the bottom.

Understanding Chromatography

Use the words below to fill-in the gaps.

A ______ substance will always produce one spot in chromatography, no matter which solvent you use. ___________ usually produce more than one _______, one for each ____________ in the mixture. It is possible that two _____________ in a mixture will show up as one spot in some solvents and you may need to ____________ the experiment with a different ___________ to distinguish between the substances.

The paper is known as the _______________ phase of chromatography because it stays still and the solvent is known as the _________________ phase because it moves up the sheet.

It is important to draw the line in _____________: if you drew the line in ink, the ink could ____________ in the solvent and disrupt the experiment. The substances that are most ___________ travel furthest up the paper. Any ____________ substances would not move up the paper at all.

stationary / insoluble / spot / substance / solvent / mobile / pencil / substances / pure / dissolve / mixtures / soluble / repeat

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Rf Values

In order to identify specific substances by chromatography, we need to calculate the retention factor for the substance.

Solvent front = the distance travelled by the solvent

New position of compound = the distance travelled by a particular dye

Origin/baseline = the pencil line on which you placed the dots of dye/ink

The calculation for the Rf value is:

Rf value = distance travelled by the substance

distance travelled by the solvent

In the example above: Rf = 2.1

2.8

= 0.75

Rf values are ALWAYS a decimal between 0 and 1, as the substance cannot move further than the solvent. If a substance had an Rf value of 0, that would mean that the ink spot did not move from the origin line because it was insoluble in the solvent.

Use the information from the diagram to calculate the Rf value for each substance in the reaction mixture:

A =

B =

C =

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For each of the following chromatograms calculate the Rf values for all of the spots.

Red = Purple =

Yellow = Light Green =

Light Blue = Orange =

Calculate the Rf value of

A, B and C and work out

which colour they are

likely to be:

Bright Blue = A =

Dark Green = B =

Dark Blue = C =

Which of these felt tip pens contained an ink that was insoluble in water? How can you tell?

____________________________

____________________________

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____________________________

____________________________

Knowledge Check

1. Name the process used to identify the dyes used in food colourings and inks.2. Explain why the origin line is drawn in pencil, not ink.

3. Describe how to place the paper into the container during chromatography.

4. Name the two phases of chromatography.

5. Suggest where the spot of the most soluble dye would be found on a chromatogram.6. Describe where a spot of an insoluble dye would be found on a chromatogram.7. State the calculation for an Rf value.

8. Calculate the Rf value when a solvent has moved 6cm and the dot of a substance has moved 1.5cm.

Target 9 extension task: [check answers in appendix]

Questions

Q1. Some food colourings are a mixture of soluble, coloured substances. Mixtures of soluble substances can be separated by paper chromatography.

Paper chromatography was used to try to separate the coloured substances in five food colourings, V, W, X, Y and Z.

Figure 3 shows the spots for the five food colourings on the chromatography paper at the start of the experiment. The paper was placed in a beaker with the bottom of the paper in the solvent.

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Figure 3(i)   Identify the stationary phase in this experiment.

(1) .............................................................................................................................................

(ii)  Give a reason why the spots of the food colourings must be above the level of the solvent when the paper is placed in the solvent.

(1) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(iii)  Figure 4 shows the chromatogram at the end of the experiment.

Figure 4Give the reason why the spot of food colouring V has not moved during the chromatography experiment.

(1) .............................................................................................................................................

.............................................................................................................................................

(iv)  Explain, by referring to Figure 4, which food colouring contained the greatest number of soluble, coloured substances.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

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.............................................................................................................................................

(v)  One coloured substance in food colouring X moved 5.8 cm when the solvent front moved 6.6 cm.

Calculate the Rf value for this substance, giving your answer to two significant figures.(2)

Rf value = ...........................................................

(Total for question = 7 marks)

 Lesson 6 – Chromatography PracticalRecall

1-2. Name the two changes of state that occur during simple distillation.

3. Beryllium is in group 2, describe how beryllium atoms become ions.4. State the charge will beryllium ions have as a result.5. Describe what happens when alkenes are tested using bromine water.

6. Describe the trend in flammability as you move up the fractionating column in fractional distillation.7. Name the type of substance that melts over a range of temperatures instead of having a distinct melting point.8. Describe how you would test to see if a gas was hydrogen.

Chromatography Recap

Use a pencil to draw a _______ 2cm from the bottom of the _______. We use pencil, not pen, because it is __________ and therefore won’t _________ up the paper. Spots of ______ are then placed on the line. A small amount of __________ (normally water) is then placed in the bottom of a beaker. The paper is then put in the beaker so that the line is __________ the

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solvent – if it was below, the ink would just go _______ into the solvent and not go up the paper. The chromatogram is left for about 15 __________ so that the solvent moves up the paper. The place where the solvent ___________ is then marked on the paper and then measured along with the ____________ moved by the dot of each ___________ in the ink. These measurements can then be used to calculate the ____________ factor (Rf).

above / insoluble / line / colour / down / distance / paper / travel / retention / minutes / ink solvent / reached

Interpreting Results

This is a chromatogram produced from a grey felt tip pen.

1. How many different coloured dyes are found in the grey ink? ________2. Calculate the retention factor (Rf) value for the purple dye.

Rf = ___________3. If you did another chromatogram of a different felt tip, how would you know if it contained the same purple dye?____________________________________________________________________________________________________

Understanding the Process

Look at the chromatography recap on the previous page and write down some important do’s and don’ts when you are doing a chromatography experiment and say why each thing is important.

Do’s Don’ts

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50

Extended writing challenge: Chromatography

The diagram shows chromatography equipment set up with two mistakes.

Identify the mistakes and explain why they need to be changed.

A, B and C are blue food colouring samples and X is an unknown substance that contains one of the food colourings. Explain how chromatography could be used to identify which food colouring the substance contained.

Knowledge Check

1. Describe how to draw the origin line on the chromatogram.

2. Name the solvent used in most chromatography experiments.3. State the term that is abbreviated to Rf.

4. Describe what would happen if the inks were below the level of the solvent.

5. Describe how you can tell if the same dye is in two different inks.

6. Name the equipment used to measure the distance travelled by the different spots of dye.7. Explain why the origin line should not the drawn in pen. 8. Suggest why a lid would be put on the beaker during chromatography.

Target 9 extension task: [check answers in appendix]

Q1. P, Q, R and S are mixtures of food colourings. They are investigated using paper chromatography. Figure 4 shows the chromatogram at the end of the experiment.

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(6 marks)

(i)  Which mixture contains an insoluble food colouring?

(1)

   A    mixture P

   B    mixture Q

   C    mixture R

   D    mixture S

Figure 4 (ii)  Give a change that could be made to the experiment to obtain an Rf value for the insoluble colouring.

(1) .............................................................................................................................................

.............................................................................................................................................

(iii)  Explain, by referring to Figure 4, which mixture is separated into the greatest number of soluble food colourings by this chromatography experiment.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

 

(Total for question = 4 marks) 

Q2. 

Mixtures of coloured substances can be separated by paper chromatography.

Paper chromatography was used to separate a mixture of blue and red inks. A spot of the mixture was placed on chromatography paper as shown in Figure 1.

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Figure 1(i)  Give a reason why the start line is drawn in pencil rather than in ink.

(1) .............................................................................................................................................

.............................................................................................................................................

(ii)  The chromatography paper, with the spot of mixture on it, was placed in a beaker with the bottom of the paper in water.

On Figure 2, complete the diagram showing the position of the chromatography paper with the spot of mixture at the start of the experiment.

(1)

Figure 2(iii)  The chromatography was carried out and the result is shown in Figure 3.

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Figure 3The blue spot had moved 14.5 cm and the solvent front had moved 15.3 cm.Calculate the Rf value of the substance in the blue spot, giving your answer to 2 significant figures.

(2)

Rf value = ........................................................... (Total for question = 4 marks)

Appendix 1 – Answers to target 9 questions

Lesson 1 – Mark Scheme

(a)     CH4 + 2O2 → CO2 + 2H2O1

(b)     toxicaccept causes death

1

acid rain

or

respiratory problemsaccept respiratory problems / asthma

1

global dimming1

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(c)    

Level 3: A judgement, strongly linked and logically supported by a sufficient range of correct reasons, is given. 5-6

Level 2: Some logically linked reasons are given. There may also be a simple judgement. 3-4

Level 1: Relevant points are made. They are not logically linked. 1-2

No relevant content 0

Indicative content•   methane is the best fuel because it gives more energy

per gram than coal, and gives less carbon dioxide per kJ of energy produced

•   petrol is best because it being a liquid is easier to handle than gas or coal - although the energy content is lower than the others, it gives out less carbon dioxide than coal

•   methane has more energy per gram than coal

•   coal produces most carbon dioxide

•   coal can produce sulfur dioxide

 

6

Lesson 2 – Mark Scheme

(a)     C3H8

1

(b)     (i)      increases / gets larger1

(ii)     all 5 points plotted correctlydeduct 1 mark for each incorrectly plotted pointbut ignore –90, 30allow error of one square in any direction

2

smooth line graph

55

 1

(iii)     boiling point estimate from their graphallow 2 °C

1

(iv)    shown clearly on graphallow just one construction line drawn

1

(c)     C9H18

1

[8]

Lesson 3 – Mark Scheme

Q3.

  Answer Acceptable answers

Mark

56

(a)

Allow CH2=CH2       Allow prope(e)n(e) only

(2)(b)(i) (molecule contains

a) double bond multiple bond(s) ignore spare bonds (1)

(b)(ii) (colour change) from orange (1) to colourless (1)

red/yellow/brown decolorised ignore clear/ discoloured (2)

(c) 1st mark long molecules/ hydrocarbon / alkane/ chain or break down/ decompose/ split (1) 2nd mark into smaller molecules / alkane / alkene / hydrocarbon/ chain or more useful product

 

  (2) (d)(i) D polymerisation   (1)(d)(ii) An explanation

linking two of the following poly(ethene) does not rot/biodegrade (1) remains for many years in landfill/ fills up land(fill) (1) (may) harm animals / landfill unsightly (1)

       

(2)

 

Lesson 4 – Mark Scheme

1. Fluorine – gas

Chlorine – gas

Bromine – liquid

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Iodine – solid

Astatine – solid

2. The boiling point of water is 100⁰C.

The boiling point of salt is 801⁰C.

If I had some salt water, what temperature would it boil at? it wouldn’t have a specific boiling point – it would boil from 100⁰C to 801⁰C.

When you have a mixture of substances, they melt and boil over a range of temperatures. Pure substances have a specific boiling point.

Lesson 5 - Mark Scheme

Q1. 

58

59

 

60

Lesson 6 - Mark Scheme

Q1. 

 

Q2. 

 

61