Crude Oil, Fuels & Organic Chemistry (WJEC GCSE Chemistry)

Kerosene is one of the fractions separated during the fractional distillation of crude oil.

Kerosene contains dodecane, C₁₂H₂₆. Dodecane undergoes a further process A to form smaller, more useful hydrocarbons, ethene, butene and one molecule of hydrocarbon X.

i) Name process A.

       [1]

ii) Complete the equation for this reaction. 

[1]

C₁₂H₂₆  C₂H₄ + C₄H₈ + ................................. 

dodecane        ethene  butene        hydrocarbon X     

Higher Tier Only

C₄H₈ has three isomers. The diagrams below show two of the three isomers.

The third isomer is methylpropene. Draw its structure.

i) Polyethene is made from ethene by addition polymerisation. Draw the structure of the repeating unit for polyethene.

[1]

ethene	repeating unit for polyethene

ii) The presence of the double bond in ethene can be confirmed using bromine water.

I. Complete the equation for the reaction between ethene and bromine.

[1]

II. Tick (✓) the box next to the name of the product formed.

[1]

In the UK, around 3 billion disposable coffee cups are used every year. Each paper coffee cup is lined with polyethene which is impossible to remove at a recycling plant. If the automated machine that sorts waste at a recycling centre detects a plastic lining, it rejects the cup sending it to general household waste.

i) Most general household waste is disposed of in landfill sites.

Apart from using landfill sites, give the other disposal method of general household waste. State an environmental problem associated with the method.

[2]

Method ........................................................................................

Problem .......................................................

ii) Recycling helps to conserve raw materials. Name the raw material used to make polyethene. Give the main reason why it is important to conserve this raw material.

[2]

Raw material ......................................................................................

Main reason .......................................................................................

The table shows the names, molecular formulae and structural formulae of some alcohols.

Complete the table.

Name	Molecular formula	Structural formula
methanol	. . . . . . . . . . . . . . . . . . . .
ethanol	C2H5OH	. . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . .	C3H7OH

The diagram shows apparatus that can be used to make ethanol by fermentation. 

i) Complete and balance the symbol equation for the reaction.

[2]

ii) Yeast acts as a catalyst in the process. Give the reason why catalysts are written above the arrow in equations.

[1]

In Brazil sugar cane is used to make ethanol which can be used instead of petrol in cars. Many people see ethanol as the fuel of the future but others are concerned with environmental and social issues.

The table shows information relating to the burning of 1 dm³ of ethanol and petrol.

Use the information in the table and your knowledge to answer the following question.

Explain one advantage and one disadvantage of using ethanol instead of petrol in cars.

Advantage ..........................................................................

Disadvantage .....................................................................

Methanol, ethanol and butanol all belong to the homologous series of alcohols.

The table shows information about two different methods for the manufacture of ethanol.

Use the information in the table and your knowledge to answer the following question.

Explain two advantages and two disadvantages of method A compared with method B.

 Advantages

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

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

Disadvantages

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

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

Ethanol is found in alcoholic drinks. Alcoholic drinks turn sour when left exposed to air because ethanol is oxidised to ethanoic acid and water.

Complete the balanced symbol equation for this reaction.

C₂H₅OH + O₂ → ....................................................

Methanol readily burns in air. The diagram shows the bonds which are broken and the bonds which are formed during the combustion of methanol.

Some relevant bond energies are shown in the table.

i) The total energy needed to break all the bonds in the reactants is 5616 kJ. The energy needed to break the bonds in one molecule of methanol is 2061 kJ.

Use this information to calculate the amount of energy needed to break one O=O bond.

[2]

Energy needed = ................................................. kJ

ii) Calculate the total energy released when all the bonds in the products are formed.

[2]

Energy released = ................................................ kJ

iii) The burning of methanol gives out heat and is said to be exothermic. Use the total energy value 5616 kJ and your answer to part (ii) to show that this is correct.

[1]

iv) On the axes below draw the energy profile for the combustion of methanol and use the symbol () to show the activation energy for the reaction.

[1]

Higher tier only

Butanol has the molecular formula C₄H₉OH. It has four positional isomers, A, B, C and D

Give the letter of the isomer corresponding to each of the names in the table.

The bar chart shows the relative supply and demand for some fractions obtained from crude oil. 

i) Use the bar chart to describe how the difference between supply and demand of the fractions changes as chain length increases.

[2]

ii) Oil companies have solved the problem of the over-supply of some fractions by using a process called cracking. C₁₄H₃₀ can be cracked forming hexene, ethene and hydrocarbon A.

I. Complete the equation for the cracking of C₁₄H_30. [1]

II. Name hydrocarbon A. ...........................

[1]

III. State why ethene is considered an important raw material.

[1]

iii) One hydrocarbon found in the C₁ - C₄ fraction is propane. Propane burns in air forming carbon dioxide and water. Balance the symbol equation that represents this reaction.

[1]

C₃H₈    +    O₂       CO₂ +    H₂O

Shale gas is natural gas trapped in rocks deep underground. Like oil and coal, shale gas has, essentially, formed from the remains of plants, animals and micro-organisms that lived millions of years ago. It can be extracted using a process known as hydraulic fracturing – or “fracking” – which involves drilling long horizontal wells into the rocks more than a kilometre below the surface. Massive quantities of water, sand and chemicals are pumped into the wells at high pressure. This opens up cracks in the shale, which are held open by the sand, enabling the trapped gas to escape to the surface for collection. 

Supporters of fracking argue that extracting shale gas deposits will help keep energy affordable and cut consumption of dirtier coal. But opponents claim fracking is dangerous and polluting, and that tapping into extra shale gas supplies will increase carbon dioxide emissions. The main controversy surrounding shale gas is the potential of fracking to contaminate drinking water supplies with shale gas or drilling chemicals. Other issues include the huge quantities of water and chemicals used in the extraction process, the waste water generated and possible earthquake tremor

i) Put a tick (✔) in the box next to the statement that identifies the substance(s) recovered during the fracking process.

[1]

ii) Put a tick (✔) in the box next to the statement which is true.

[1]

Mountaineers often choose an ethanol burner when hiking in extremely cold conditions.

A group of students was asked to investigate how the mass of ethanol burned is related to the amount of energy given out.

Four students each burned a different mass of ethanol and recorded the temperature rise of 250 g of water. The diagram shows the apparatus used by each of the students.

They used their results to calculate the energy given out.

The table shows the students’ results.

The temperature rise can be calculated using the formula below.

energy given out (J) = 4.2 × temperature rise (°C) × mass of water (g)

Use this formula to calculate the temperature rise recorded by student D.

Temperature rise = ........................... °C

Plot the energy given out against mass of ethanol burned on the grid below and draw a suitable line. 

Describe the relationship between the mass of ethanol burned and the energy given out.

All the recorded temperature rises were lower than expected.

Explain one piece of advice you would give the students to resolve this problem.

A student investigated the temperature rise during a neutralisation reaction.

The student put 25.0 cm³ of sodium hydroxide solution and 5 drops of universal indicator into a polystyrene cup and recorded the temperature of the alkali. After 10 seconds the student added 25.0 cm³ of dilute hydrochloric acid to the alkali and recorded the temperature every 5 seconds for another 30 seconds. Graph A shows the results obtained.

i) Use the graph to find the maximum temperature rise during the reaction.

[1]

Temperature rise = ........................................................ °C

ii) The energy given out can be calculated using the following formula.

energy given out = total volume of reaction mixture × 4.2 × temperature rise

Calculate the energy given out during the reaction.

[2]

Energy given out = ....................................................... J

iii) The temperature of the contents in the cup was recorded after 2 hours. Give the final temperature reading you would expect. Give the reason for your answer.

[1]

Final temperature ........................................................ °C

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

The student repeated the experiment using 25.0 cm³ of ethanoic acid of the same concentration as the hydrochloric acid. The table shows the results obtained.

Plot the results on the grid. Draw a suitable line. Label your graph B.

Use the graphs to state which of the two acids is the stronger – hydrochloric acid or ethanoic acid. Give the reason for your choice.

Acid ..................................................................................

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

The temperature rises in both experiments were much lower than expected. The student suggested that using a temperature sensor instead of a thermometer would give temperature rises closer to the expected values.

i) State why using a temperature sensor would still give a lower than expected temperature rise.

[1]

ii) What improvement to the apparatus would you suggest to the student to obtain  temperature rises closer to the expected values?

[1]

Use the information from the table below to evaluate the potential of hydrogen as a replacement for petrol and diesel to fuel cars.

Your answer should include both advantages and disadvantages.

Alkenes such as ethene are reactive hydrocarbons. They can be recognised by their reaction with bromine, Br₂.

i) State what you would expect to see when bromine water is added to an alkene. Give the reason this happens.

 [2]

ii) Complete the equation by giving the structure of the product formed.

[1]

Monomers can undergo polymerisation to form polymers. One example is PVC.

i) Complete the equation for the formation of PVC.

[1]

ii) PVC is a thermoplastic. Describe the effect of heat on thermoplastics and explain in terms of their structure why they behave in this way.

[3]

A new plastic called ‘NPFC’ has been developed.

‘NPFC’ has the following properties.

• easy to colour with dyes

• poor conductor of heat

• easy to cut with a knife

• starts to soften at 50°C

• biodegradable

A food company investigated the use of this plastic to make containers for take away fish and chips.

State the property which makes ‘NPFC’ a good material for a disposable container and give a reason for your answer.

Using the properties given, explain why the food company decided not to use ‘NPFC’ to make fish and chip containers.

The following diagram shows an experiment that could be carried out in the laboratory to obtain ethene from decane, C₁₀H₂₂.

i) Complete the following symbol equation for the reaction taking place.

[1]

   C₁₀H₂₂ → .................... + C₂H₄ 

ii) Name the process which has taken place.

[1]

Ethene is a hydrocarbon.

The following diagram shows apparatus that can be used to investigate the products formed when ethene is burned.

i) State what you would expect to happen to the limewater in test tube B and give the reason for your answer.

[1]

ii) The experiment was repeated with hydrogen being burned instead of ethene.

I. State what would be seen in test tube A. Give a reason for your answer.

[2]  

II. State and explain what would be seen in test tube B.

[2]

Crude oil is a source of some very important fuels. State how crude oil was formed.

Crude oil is a mixture of compounds called hydrocarbons. They are separated into different fractions in a fractionating column.

i) State what happens to the crude oil in X before it is allowed to enter the fractionating column.

[1]

ii) State the property of hydrocarbons which allows them to be separated using this method.

[1]

A similar process can also be used to separate gases from air.

The table below shows the boiling points of three gases that can be obtained from air.

To separate the gases, air is compressed and cooled to become liquid air. The liquid air is then allowed to warm up slowly.

State which of the three gases boils first when liquid air warms up and give the reason for your answer.

The fire triangle is used in fighting fires. State what is meant by the term ‘fire triangle’ and how it is used to fight fires.

The pictures below show two methods of fighting fires. State how each method puts out the fire.

Method 1

Method 2

Fire fighters use their understanding of the fire triangle to put out fires. Every year thousands of acres of moorland are destroyed by fire. Fire fighters use several different methods to put out this type of fire.

Suggest three different methods that could be used to put out moorland fires. Each method should refer to a different part of the fire triangle. State how each method is effective.

Method 1

Method 2

Method 3

The table below shows the relative ‘supply of’ and ‘demand for’ some fractions obtained from a sample of crude oil from the North Sea.

Give a reason why market demand for the C₅ - C₈ fraction is high.

The supply of the C₅ - C₈ fraction is less than the market demand. Explain how oil companies overcome this problem.

One hydrocarbon found in the C₁ - C₄ fraction is propane. Propane burns in air forming carbon dioxide and water.

Balance the symbol equation that represents this reaction.

C₃H₈ + O₂ → CO₂ + H₂O

The table below shows the names, molecular formulae and the structural formulae of the first two members of the alkene series. Complete the table by giving the structural formula of butene, C₄H₈.

Name	Molecular formula	Structural formula
ethene	C2H4
propene	C3H6
butene	C4H8

Explain how polypropene is formed from propene.

Ethanol can be used as a fuel. It can be made by the fermentation of sugars using yeast.

The following graph shows the rate of fermentation using different sugars at 25 ^oC.

Identify the best sugar for producing ethanol and give a reason for your choice.

Best sugar ................................................................................................................

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

The following statements relate to the use of ethanol as a fuel.

      It is a renewable resource

      Large areas of land required to grow the crops

      Produces less soot than petrol when burnt

      Engines require modifications to run on ethanol

      Produces less heat per litre than petrol

      Produces only carbon dioxide and water when burnt

i) In your opinion, should ethanol be used as a fuel? Give reasons to support your answer.

[3]

Opinion (Yes/No) ..................................................

Reasons ....................................................................................................

ii) Complete the word equation for the complete combustion of ethanol.

[1]

ethanol + oxygen → ........................................ + ........................................

The following diagram shows the structures of six organic compounds.

Name the family to which each of the following pairs of compounds belong.

B and D ..................................................

E and F ..................................................

Describe a chemical test that could be carried out to distinguish between compounds C and E. Give the expected result for both compounds.

Higher tier only

Compound C is one of two isomers that have the molecular formula C₄H₁₀.

i) Give the meaning of the term isomer.

[1]

ii) Draw the structure of the other isomer of C₄H₁₀.

[1]

Higher tier only

Give the letter, A - F, of one other compound that has an isomer. Draw the structure of its isomer.

Compound .......................................

Structure

Plastics have replaced many traditional materials. The diagrams show plastics being used for three different types of food and drink packaging and containers.

Describe the advantages and disadvantages of using plastics in these examples.

Microplastics in the Ocean

Plastics are used in many areas of modern life.

Figure 1 shows the amount of plastic production between 1950 and 2013.

Figure 1

One of plastic’s greatest properties, its durability, is also one of the main reasons that plastics present a threat to the marine environment.

The term ‘microplastic’ is used to describe plastic particles that are less than 5 millimetres in diameter, which includes particles as small as 10 nanometres. Microplastics can be found in some cosmetic products, toothpastes and soaps.

Microplastics are spread throughout the oceans and are found on shorelines from the Arctic to Antarctica. Figure 2 shows the number of microplastic pieces found in sea ice at four Arctic sites during a survey in 2014.

Microplastics have been found inside the bodies of marine animals. Microplastics often contain chemicals that can absorb poisons such as pesticides from the surrounding seawater. There is strong evidence of transfer of poisons from eaten microplastics into animal tissues. Nano-size microplastics have been shown to cross cell membranes, under laboratory conditions, causing tissue damage.

Public awareness of the potential for microplastics to damage marine animals is low compared with that of the impact of plastic litter in our seas and oceans. Effective education of society is essential to raise awareness of the damaging effects of microplastics.

i) Put a tick (✓) in the box next to the size of microplastics.

[1]

ii) Put a tick (✓) in the box next to the statement that best describes the amount of plastic produced in Europe since 2002.

[1]

iii) Name the type of plastic most often found in the Arctic microplastic survey.

[1]

iv) Put a tick (✓) in the box next to a hypothesis which needs further testing by scientists.

[1]

v) Suggest a method of educating people of the hazards of microplastics.

[1]

The table shows the first four members of the alkane family.

Give the general formula for the alkane family.

Higher tier only

C₄H₁₀ has two isomers. The diagram below shows the structure of one of the isomers, butane.

Draw and name the other isomer.

 Isomer structure

 Name of isomer ............................................................................................................

The flow diagram shows two reactions of propene.

Draw the structural formula for compound A and the repeating unit in polymer B

A student was given a colourless liquid. He suspects the liquid is ethanol.

Describe a chemical test that he could carry out to positively identify the liquid as ethanol. Include the observation he would make.

 Test ...................................................................................................

 Observation ......................................................................................

Hight tier only

Organic compounds can also be identified using infrared spectroscopy.

The infrared spectra of ethanol, ethanoic acid and one other compound are shown on the opposite page.

Use the information in the table to identify the spectra belonging to ethanol and ethanoic acid.

 Ethanol ......................................................

 Ethanoic acid ......................................................

Describe the benefits and drawbacks associated with the recycling of plastic household waste.

Explain, giving examples, why plastics have replaced traditional materials such as iron, glass and wood for making many everyday things.

A - F are the structural formulae for some organic compounds.

Give the letters of the two structural formulae that are identical.

.................................. and ..................................

State which structural formula is incorrect. Give a reason for your answer.

Higher tier only

Draw the structural formula of the isomer of C₅H₁₂ not shown in part (a).

Describe a chemical test to distinguish between compounds C and E.

Higher tier only

The table below shows the first five members of the alkane family.

i) Give the molecular formula for the alkane which contains 18 hydrogen atoms.

[1]

ii) C₅H₁₂ has three isomers. The diagram below shows one of these isomers.

Draw the other two isomers.

[2]

Isomer 1

i) The first two members of the alkene family are ethene, C₂H₄, and propene, C₃H₆. Give the general formula for the alkene family.

[1]

ii) Draw the structural formula for propene.

[1]

Higher tier only

Study the infrared spectra of propane and propene below.

Using the information in the table below, identify the spectrum of propene and give a reason for your answer.

Spectrum ........................................  

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

This question is about the processes and reactions which occur in the petrochemical industry. 

Figure 1 shows some of these processes and reactions. 

Figure 1

Describe how crude oil is separated into fractions.

Describe the conditions required in reactor 1.

Name the reaction that occurs in reactor 2. 

Compare the properties of gasoline and fuel oil.

This question is about alcohols.

Alcohols have the general formula C_nH_2n+1OH.

Draw the displayed formula of propanol. 

Alcohols undergo combustion reactions.

Write a balanced symbol equation for the complete combustion of butanol. 

Figure 1 shows two methods of ethanol production. 

Figure 1

Explain how ethanol is made from sugar solution.

Give the name of the process. 

This question is about alkenes.

Draw the displayed formulae of butene.

The structures of an alkane and an alkene are shown below.

Compare the structures and reactions of propene with propane.

Write a balanced symbol equation for the incomplete combustion of ethene to form carbon monoxide and water.

This question is about cracking. 

Cracking is used to break down large alkanes into smaller hydrocarbons.

A long chain alkane is cracked to produce the following products:

C₂₀H₄₂    →     C₁₂H₂₆    +  C₅H₁₀   +   C₃H₆

Suggest one use of the product with the formula C₃H_6. 

The market demand for shorter chain alkanes is greater than the market demand for long chain alkanes.

Suggest one reason why.

C₂₀H₄₂ can also be cracked to give C₁₆H₃₄ and ethene.

Write a balanced symbol equation for this reaction.

When bromine water is added to the products of the reaction in part (d), one of the products forms a colourless solution.

Draw the displayed formula of the product that produces this colourless solution.