Specification Points

Year 10 – Organic Chemistry

Crude oil, hydrocarbons and alkanes Crude oil is a finite resource found in rocks made from the remains of an ancient biomass, mainly plankton that was buried in mud. Crude oil is a mixture of a very large number of compounds, mainly hydrocarbons (molecules made of hydrogen and carbon only). Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. Alkanes are a homologous series with a general formula of CnH2n+2 The first four members of the alkanes are methane, ethane, propane and butane. Alkane molecules can be represented in the following forms: C2H6 or structural formula.

Fractional distillation and petrochemicals Hydrocarbons in crude oil can be separated into fractions by fractional distillation by evaporating the oil and allowing it to condense at different temperatures. Fractions contain molecules with a similar number of carbon atoms. The fractions are 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.

Properties of hydrocarbons Some properties of hydrocarbons depend on the size of their molecules, including boiling point and viscosity which increase with increasing molecular size and flammability which decreases with increasing molecular size. These properties influence how hydrocarbons are used as fuels. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water and energy. Students should be able to write balanced equations for the complete combustion of hydrocarbons with a given formula. Knowledge of trends in properties of hydrocarbons is limited to boiling points, viscosity and flammability.

Cracking and alkenes Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules. This process involves heating the hydrocarbons to vaporise them. The vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur. Be able to balance cracking equations. The products of cracking include alkanes and another type of hydrocarbon called alkenes. Alkenes are more reactive than alkanes and react with bromine water, turning it from orange to colourless. Cracking produces small molecules which have high demand for use in fuels. Alkenes are used to make polymers and as starting material to make many other chemicals.

Organic Chemistry

Structure and formulae of alkenes Alkenes are hydrocarbons with a double carbon to carbon bond. The general formula for the homologous series of alkenes is CnH2n Alkenes are unsaturated, they have two fewer hydrogen atoms than the comparable alkane The first 4 members of the homologous series are ethene, propene, butene and pentene. Alkene molecules can be represented in the following forms: C3H6 or structural formulae.

Reactions of alkenes Alkenes are hydrocarbons with the functional group C=C. Alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons, but they tend to burn in air with smoky flames because of incomplete combustion. Alkenes react with hydrogen, water and the halogens, by the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond. The addition of hydrogen to an alkene (unsaturated) takes place in the presence of a catalyst to produce the corresponding alkane (saturated). The addition of water to an alkene takes place by reaction with steam in the presence of a catalyst to produce an alcohol. Addition of a halogen to an alkene produces a saturated compound with two halogen atoms in the molecule, eg: ethene reacts with bromine to produce dibromoethane. Students should be able to draw fully displayed structural formulae of the first four members of the alkenes and the products of their addition reactions with hydrogen, water, chlorine, bromine and iodine.

Polymers Polymers have very large molecules. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.

Addition polymerisation Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. In addition polymerisation reactions, many small molecules (monomers) join together to form very large molecules (polymers). Students should be able to: • recognise addition polymers and monomers from diagrams in the forms shown and

from the presence of the functional group C=C in the monomers • draw diagrams to represent the formation of a polymer from a given alkene monomer • relate the repeating unit to the monomer.

Ceramics, polymers and composites Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone. Borosilicate glass, made from sand and boron trioxide, melts at higher temperatures than soda-lime glass. Clay ceramics (pottery and bricks) are made by shaping wet clay and then heating in a furnace. The properties of polymers depend on what monomers they are made from and the conditions under which they are made. For example, low density (LD) and high density (HD) poly(ethene) are produced from ethene using different catalysts and reaction conditions. Thermosoftening polymers consist of individual, tangled polymer chains and melt when

they are heated. Thermosetting polymers consist of polymer chains with cross-links between them and so they do not melt when they are heated. Most composites are made of two materials, a matrix or binder surrounding and binding together fibres or fragments of the other material, which is called the reinforcement. Examples of composites include wood, concrete and fibreglass. Some advanced composites are made using carbon fibres or carbon nanotubes instead of glass fibres. Students should be able to, given appropriate information: • compare quantitatively the physical properties of glass and clay ceramics, polymers,

composites and metals • explain how the properties of materials are related to their uses and select

appropriate materials.

Independent Study suggestions

1. Look at the specification points above – use the textbook pages, first edition (238-247) and second edition 244-254) or the revision guide pages (150-151) to make a few notes/spider diagram/revision cards

2. Have a go at the questions in the revision guide on pages 153-156

3. Watch the Fuse School short 3-4 minute explanation videos on any area you need extra help with:

Coal, oil and gas: https://www.fuseschool.org/topics/59/contents/828

Fractional distillation: https://www.fuseschool.org/topics/59/contents/269

Uses of crude oil fractions: https://www.fuseschool.org/topics/59/contents/830

Functional groups: https://www.fuseschool.org/topics/59/contents/270

Formulae of organic compounds: https://www.fuseschool.org/topics/59/contents/268

Alkanes and Alkenes: https://www.fuseschool.org/topics/59/contents/233

Complete and incomplete combustion: https://www.fuseschool.org/topics/65/contents/330

Isomers: https://www.fuseschool.org/topics/59/contents/1198

Cracking: https://www.fuseschool.org/topics/59/contents/273

Alkenes and bromine water: https://www.fuseschool.org/topics/59/contents/829

Halogenation: https://www.fuseschool.org/topics/59/contents/883

Polymers: https://www.fuseschool.org/topics/59/contents/1000

Making polyethene: https://www.fuseschool.org/topics/59/contents/943

Polymers from chloroethene an propene https://www.fuseschool.org/topics/59/contents/279

Thermosetting polymers: https://www.fuseschool.org/topics/59/contents/972

4. You might not want to have a go at the past paper questions which follow which you can mark with the markscheme.

Q1.This question is about organic compounds.

Hydrocarbons can be cracked to produce smaller molecules.

The equation shows the reaction for a hydrocarbon, C18H38

C18H38 → C6H14 + C4H8 + 2 C3H6 + C2H4

(a) Which product of the reaction shown is an alkane?

Tick one box.

C2H4

C3H6

C4H8

C6H14

(1)

(b) The table below shows the boiling point, flammability and viscosity of C18H38 compared with the other hydrocarbons shown in the equation.

Boiling point Flammability Viscosity

A highest lowest highest

B highest lowest lowest

C lowest highest highest

D lowest highest lowest

Which letter, A, B, C or D, shows how the properties of C18H38 compare with the properties of C2H4, C3H6, C4H8 and C6H14?

Tick one box.

A

B

C

D

(1)

(c) The hydrocarbon C4H8 was burnt in air.

Incomplete combustion occurred.

Which equation, A, B, C or D, correctly represents the incomplete combustion reaction?

A C4H8 + 4O → 4CO + 4H2

B C4H8 + 4O2 → 4CO + 4H2O

C C4H8 + 6O2 → 4CO2 + 4H2O

D C4H8 + 8O → 4CO2 + 4H2

Tick one box.

A

B

C

D

(1)

Q2.This question is about hydrocarbons.

(a) Most of the hydrocarbons in crude oil are alkanes.

(i) Large alkane molecules can be cracked to produce more useful molecules.

The equation shows the cracking of dodecane.

Give two conditions used to crack large alkane molecules.

1 ................................................................................................................

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

(ii) The products hexene and ethene are alkenes.

Complete the sentence.

When alkenes react with bromine water the colour changes from orange to .................................................. .

(1)

(iii) Butane (C4H10) is an alkane.

Complete the displayed structure of butane.

(1)

(b) A group of students investigated the energy released by the combustion of four hydrocarbon fuels.

The diagram below shows the apparatus used.

Each hydrocarbon fuel was burned for two minutes.

Table 1 shows the students’ results.

Table 1

After two minutes

Name and formula of hydrocarbon fuel

Mass of fuel used

in g

Temperature increase of water in °C

Energy released by fuel in

kJ

Energy released

by 1.0 g of fuel in kJ

Relative amount of smoke in the flame

Hexane, C6H14 0.81 40 16.80 20.74 very little smoke

Octane, C8H18 1.10 54 22.68 20.62 some smoke

Decane, C10H22

1.20 58 24.36 smoky

Dodecane, C12H26

1.41 67 28.14 19.96 very smoky

(i) Calculate the energy released by 1.0 g of decane in kJ.

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

Energy released = ...................................... kJ (2)

(ii) Suggest one improvement to the apparatus, or the use of the apparatus, that would make the temperature increase of the water for each fuel more accurate.

Give a reason why this is an improvement.

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

(iii) The students noticed that the bottom of the beaker became covered in a black substance when burning these fuels.

Name this black substance.

Suggest why it is produced.

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(iv) A student concluded that hexane is the best of the four fuels.

Give two reasons why the results in Table 2 support this conclusion.

1 ................................................................................................................

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2 ................................................................................................................

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

(c) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.

Most car engines use petrol as a fuel.

• Petrol is produced from the fractional distillation of crude oil.

• Crude oil is a mixture of hydrocarbons.

• Sulfur is an impurity in crude oil.

Car engines could be developed to burn hydrogen as a fuel.

• Hydrogen is produced from natural gas.

• Natural gas is mainly methane.

Table 2 shows information about petrol and hydrogen.

Table 2

Petrol Hydrogen

State of fuel at room

temperature Liquid Gas

Word equation for

combustion of the fuel petrol + oxygen → carbon

dioxide + water

hydrogen + oxygen →

water

Energy released from

combustion of 1 g of the fuel

47 kJ 142 kJ

Describe the advantages and disadvantages of using hydrogen instead of petrol in car engines.

Use the information given and your knowledge and understanding to answer this question. (6)

(Total 18 marks)

Q3.A student investigated the viscosity of liquid hydrocarbons.

A viscous liquid is a liquid that flows slowly.

The student used this method.

• Measure 50 cm3 of the liquid hydrocarbon.

• Pour the liquid hydrocarbon into the funnel, as shown in Figure 1.

• Time how long it takes for all of the liquid hydrocarbon to run out of the funnel.

• Repeat the experiment for other liquid hydrocarbons.

(a) (i) Give the name of apparatus A in Figure 1.

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

(ii) Name the apparatus that could be used to measure 50 cm3 of liquid hydrocarbon.

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

(b) The student’s results for six liquid hydrocarbons are shown in Table 1.

Table 1

Formula of liquid hydrocarbon

Time for liquid hydrocarbon to run out of the funnel in seconds Mean time in

seconds Experiment 1 Experiment 2 Experiment 3

C5H12 12 11 13 12

C6H14 14 15 15 15

C7H16 19 20 18

C8H18 27 26 28 27

C10H22 46 48

47

C12H26 65 67 69 67

(i) The student did the experiment three times with each liquid hydrocarbon.

Give two reasons why.

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

(ii) Use the data in Table 1 to calculate the mean time, in seconds, for C7H16

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Mean time = ................................... seconds (1)

(iii) Complete the sentence.

As the number of carbon atoms in a molecule of liquid hydrocarbon increases, the time taken for the liquid hydrocarbon to run out of the funnel ................................................ .

(1)

(iv) A ring has been drawn around one result in Table 1.

This result has not been used to calculate the mean time for C10H22

Suggest why this result was not used.

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

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

(v) Suggest one error the student may have made to get the ringed result.

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

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

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

(c) The student investigated the effect of temperature on the viscosity of one of the liquid hydrocarbons.

The liquid hydrocarbon he was using had the hazard symbols shown in Figure 2.

(i) Suggest why the student warmed the liquid hydrocarbon using warm water and not a Bunsen flame.

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

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

(ii) The student wore safety glasses.

Give one other safety precaution the student should take, and give a reason for this safety precaution.

Safety precaution .................................................................................

Reason .................................................................................................

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

(d) This is the method the student used to investigate the effect of temperature on the viscosity of one of the liquid hydrocarbons.

• Measure 50 cm3 of the liquid hydrocarbon and pour it into a beaker.

• Stand the beaker of liquid hydrocarbon in a heated water bath.

• Leave for a few minutes.

• Measure the temperature of the liquid hydrocarbon.

• Pour the liquid hydrocarbon into the funnel, as shown in Figure 3.

• Time how long it takes for all of the liquid hydrocarbon to run out of the funnel.

• Repeat the experiment at different temperatures.

(i) The student’s results are shown in Table 2.

Table 2

Temperature of liquid

hydrocarbon in °C Time to run out of the

funnel in seconds

23 27

30 21

37 17

46 16

55 11

65 9

Plot the results shown in Table 2 on the graph in Figure 4.

Draw a curve of best fit.

(3)

(ii) One of the points is anomalous.

Draw a ring around the anomalous point on your graph. (1)

(iii) Predict how long it will take the liquid hydrocarbon to run through the funnel at 70 °C.

Show your working on your graph.

Time = ........................................ seconds

(2)

(iv) Describe the relationship between the temperature of the liquid hydrocarbon and the viscosity of the liquid hydrocarbon.

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............................................................................................................... (3)

(v) The apparatus the student used in Figure 2 could lead to a systematic error in the results. Identify one source of systematic error, and describe how the student could avoid or reduce the error.

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

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

(Total 22 marks)

Q4. Crude oil is a mixture of mostly alkanes.

(a) Crude oil is separated into useful fractions by fractional distillation.

(i) Describe and explain how the mixture of alkanes is separated by fractional distillation.

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.......................................................................................................................... (3)

(ii) The table gives the name and formula for each of the first three alkanes.

Complete the table to show the formula of butane.

Name of alkane Formula

Methane CH4

Ethane C2H6

Propane C3H8

Butane

(1)

(b) The structural formula of methane, CH4, is:

H │ H │ H

Draw the structural formula of propane, C3H8

(1)

(c) The relative amounts of and the market demand for some hydrocarbons from the fractional distillation of crude oil are shown in the graph.

(i) Why is the market demand for the C5 – C8 fraction higher than the market demand for the C21 – C24 fraction?

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

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

(ii) Cracking is used to break down large hydrocarbon molecules into smaller hydrocarbon molecules.

Complete the symbol equation by writing in the formula of the other hydrocarbon.

C20H42 C16H34 + 2 .......................................... (1)

(iii) The C5 – C8 fraction has low supply and high market demand.

Suggest three ways in which the oil industry could overcome this problem.

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3 .......................................................................................................................

.......................................................................................................................... (3)

(Total 10 marks)

Q5. To make a plastic, such as poly(ethene), from crude oil involves many processes.

(a) Describe how crude oil is separated into fractions.

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

(b) Ethene is produced by cracking the hydrocarbons in the naphtha fraction.

(i) Balance the symbol equation for this reaction.

C10H22

decane → C4H10

butane + C2H4

ethene

(1)

(ii) Describe how cracking is carried out.

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

(c) Alkanes, such as butane (C4H10), do not form polymers.

Alkenes, such as ethene (C2H4), do form polymers.

Explain these statements.

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

(d) Ethene molecules form the polymer poly(ethene). One molecule in poly(ethene) will contain thousands of carbon atoms. The diagram represents part of a poly(ethene) molecule.

Propene molecules form the polymer poly(propene).

Draw a diagram to represent part of a poly(propene) molecule.

(2)

(Total 9 marks)

Answers:

M1.(a) C6H14

1

(b) A 1

(c) B 1

M2.(a) (i) high temperature

allow heating / hot / 250-900 °C 1

catalyst or steam

allow named catalyst eg zeolite, Al2O3, silica, ceramic

allow in the absence of air / oxygen 1

ignore any references to pressure

(ii) colourless

allow decolourised

ignore clear / discoloured 1

(iii) 1

(b) (i) 20.3(0) (kJ)

if answer incorrect allow 1 mark for 24.36/1.2 2

(ii) use a lid

allow insulate beaker or use draught shield 1

reduce energy / heat loss

ignore references to thermometer or repeats or distance of flame or loss of water vapour

allow stir (1) to distribute energy / heat (1)

allow use a metal can (1) as it’s a better conductor (1) 1

(iii) carbon/soot

ignore tar, smoke 1

(produced by) incomplete combustion

allow from a limited supply of oxygen/air 1

(iv) hexane gives out the greatest energy (per 1.0 g)

ignore more energy 1

hexane produces the least smoke / carbon / soot

allow has the cleanest flame

ignore less smoke / carbon / soot 1

(c) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should also apply a ‘best-fit’ approach to the marking.

Level 3 (5 – 6 marks): Descriptions of advantages and disadvantages that are linked to their own knowledge.

Level 2 (3 – 4 marks): Descriptions of an advantage and a disadvantage with some use of their knowledge to add value.

Level 1 (1 – 2 marks): Statements made from the information that indicate whether at least one statement is an advantage or a disadvantage or a linked advantage or disadvantage

0 marks: No relevant content

Examples of the added value statements and links made in the response could include: Note that link words are in bold; links can be either way round. Accept reverse arguments and ignore cost throughout.

Advantages of using hydrogen: • Combustion only produces water so causes no pollution • Combustion does not produce carbon dioxide so this does not contribute to global warming or climate change • Combustion does not produce sulfur dioxide so this does not contribute to acid rain • Incomplete combustion of petrol produces carbon monoxide that is toxic • Incomplete combustion of petrol produces particulates that contribute to global dimming • Petrol comes from a non-renewable resource but there are renewable/other methods of producing hydrogen • Hydrogen releases more energy so less fuel needed or more efficient

Disadvantages of using hydrogen: • Hydrogen is a gas so is difficult to store or transfer to vehicles • Hydrogen gas is very flammable so leaks cause a greater risk of explosion • Most hydrogen is produced from fossil fuels which are running out • Cannot be used in existing car engines so modification / development or replacement is needed • Lack of filling stations so difficult to refuel your vehicle

6

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M3.(a) (i) (conical) flask 1

(ii) measuring cylinder / pipette / burette 1

(b) (i) any two from: • so anomalous results could be identified / ignored • so a mean / average could be taken • (to improve) accuracy

2

(ii) 19 1

(iii) increases / gets longer / gets bigger 1

(iv) anomalous / does not agree with other times for C10H22

1

(v) any one from: • shorter hydrocarbon used • volume of hydrocarbon too small • started timing late • stopped timing too early / when liquid left in funnel

must suggest why the result is lower than the others.

allow the temperature was higher or the students used a wider funnel. 1

(c) (i) flammable 1

(ii) suitable safety precaution 1

reason that links the safety precaution to the hazard symbols

eg:

• wear gloves

• (because) it is hazardous to health / harmful / toxic / irritant

or

• do not pour down sink or dispose of properly

• (because) it is harmful to the environment / kills fish

or

• wear a mask or do it in the fume cupboard or a well-ventilated area

• respiratory irritant 1

(d) (i) points plotted correctly (within half small square)

all six points correct scores 2

3, 4 or 5 points correct scores 1 2

smooth curve of best fit 1

(ii) point at 46 °C circled

allow point furthest from the line as drawn 1

(iii) working shown on graph 1

value read from graph line drawn (within half small square) 1

(iv) the higher the temperature the lower the viscosity

allow the higher the temperature the lower / shorter the time taken for 1 mark 2

non-linear or change gets smaller as temperature gets higher

answer relating temperature to time taken can score a maximum of 2 marks. 1

(v) identifying source of the error 1

method of avoiding the error

eg:

• the temperature will drop

• insulate the funnel

or

• runs out before all added

• put a tap on the funnel 1

[22]

M4. (a) (i) heat / evaporate the crude oil / change to gas or vapour

do not accept heat with catalyst 1

cool / condense (hydrocarbons)

allow small molecules at top and / or large molecules at bottom 1

at different temperatures / boiling points

if the answer describes cracking ‘ no marks 1

(ii) C4H10

1

(b) H H H │ │ │ H ─C ─ C ─ C ─ H │ │ │ H H H

1

(c) (i) C5 to C8 fraction are fuels or easier to burn or petrol (fraction)

accept C21 to C24 fraction not useful as fuels

do not accept produce more energy 1

(ii) C2H4

do not accept C4H8

1

(iii) any three from:

• use different / lighter crude oils

• develop markets for low demand fractions

• develop new techniques / equipment to use low demand fractions as fuels

• cracking

• convert low demand fractions to high demand fractions or bigger molecules to smaller molecules

• develop alternative / bio fuels

do not accept price 3

[10]

M5. (a) vaporise / evaporate

allow boil for vaporise 1

different condensing points / temperatures

accept condense at different levels

ignore different size molecules or different densities

mention of cracking = max 1

allow boils at different temperatures and condenses for 2 marks

if no other marks awarded allow

fractional distillation for 1 mark 1

(b) (i) 3 (C2H4)

accept +C4H8

1

(ii) (decane / naphtha / hydrocarbon) vaporise / evaporate

allow crude oil

allow boil for vaporise

1

(passed over) a catalyst / alumina / porous pot

ignore other names of catalysts 1

(c) any two from:

‘they’ must be clarified

• alkanes / butane (molecules) do not have a (carbon carbon) double bond / are saturated / have (carbon carbon) single bonds

• alkenes / ethene (molecules) have (carbon carbon) double bonds

or are unsaturated

• alkenes / ethene molecules are able to bond to other molecules 2

(d) single bonds between carbon atoms

– C - C – 1

the -CH3 group appears on each pair of carbons on the ‘chain’

NB any double bonds = 0 marks 1

[9]