Fuels (Edexcel GCSE Chemistry): Exam Questions

Which molecule can be cracked to produce hexane, C₆H₁₄? 

Crude oil is a mixture of hydrocarbons.

It can be separated into fractions.

Which of these mixtures shows formulae of substances that could be in the gaseous fraction of crude oil?

Figure 11 shows the percentages of the fractions in crude oil from three different oil wells.

Figure 11

i) State which oil well produces a crude oil containing the highest percentage of the high boiling point fractions.

(1)

ii) A barrel of crude oil from oil well B weighs 130 kg.

Calculate the mass of kerosene in this barrel.

(1)

Diesel is the fuel used in most bus engines.

Research is being carried out into the use of hydrogen, instead of diesel, as a fuel for buses.

Discuss the advantages and disadvantages of using hydrogen, rather than diesel, as a fuel for buses.

Fractions of crude oil contain alkanes.

A sample of decane, C₁₀H₂₂, was cracked using the apparatus in Figure 12.

This produced a mixture of products, including ethene.

Figure 4

i) Explain how ethene is produced using the apparatus in Figure 4.

(3)

ii) One molecule of decane produced two molecules of propene, C₃H₆, and one molecule of product Z.

C₁₀H₂₂ → 2C₃H₆ + product Z

What is the formula of product Z?

(1)

iii) When decane undergoes complete combustion, a mixture of carbon dioxide and water is formed. Complete the balanced equation for this reaction.

(2)

2C₁₀H₂₂ + .......... O₂ → .......... CO₂+ .......... H₂O

Pollutants released from burning fuels can negatively affect health and the environment.

Which of the following is not the correct effect for the given pollutant? 

Crude oil is found in the Earth’s crust.

Which of the statements about crude oil is correct?

The substances ethane, C₂H₆, octane, C₈H₁₈, and pentadecane, C₁₅H₃₂, are all found in crude oil.

These substances

i) Use a word from the box to complete each of the sentences about the fractional distillation of crude oil.

Each word may be used once, more than once, or not at all.

(2)

The separation of crude oil into fractions occurs in a fractional distillation column. Before crude oil is passed into the column it is ................................................. .

During the distillation, vapour rises up the column until it is cold enough for the vapour to form a liquid. The vapour has been ................................................... .

ii) Complete this sentence by underlining the correct answer in the box.

(1)

Compared with the fraction from the top of the column,

When crude oil is separated into fractions, the amount of each fraction obtained rarely matches the demand for that fraction.

Figure 7 shows the relative amounts of four of the fractions obtained from a crude oil and the relative demand for each of these fractions.

Figure 7

State the fraction for which the relative amount obtained exceeds the relative demand.

In January 2015 the United Kingdom produced 850 000 barrels of crude oil per day. 45% of this crude oil was fuel oil.

Calculate the number of barrels of fuel oil present in the 850 000 barrels of crude oil.

Give your answer to two significant figures.

Incomplete combustion occurs when there is insufficient oxygen for a reaction.

Which are the two main substances formed during incomplete combustion, aside from water?

Crude oil is a complex mixture of substances.

Crude oil can be separated into useful fractions by fractional distillation.

Figure 7 shows a fractional distillation column and the fractions produced when a sample of crude oil is distilled.

Figure 7

The properties of these fractions vary from the top of the column to the bottom of the column.

Which of the following is a trend in a property of the fractions obtained from the top of the column to those obtained from the bottom?

Most of the substances in crude oil are alkanes.

i) Which of the following is the general formula of an alkane?

(1)

ii) Explain why alkanes are described as hydrocarbons.

(2)

Figure 8 shows a graph of the boiling points of some alkanes against the number of carbon atoms in one molecule of each alkane.

Figure 8

Explain the pattern shown by this graph.

When crude oil is separated into fractions, the amount of each fraction obtained rarely matches the demand for that fraction.

Figure 9 shows the relative amounts of six of the fractions present in a crude oil and the relative demand for each of these fractions.

Figure 9

Cracking is used to match the relative amount of a fraction of crude oil to the demand for that fraction.

i) Use the information in Figure 9 to give the name of the fraction that is most likely to need to be cracked.

(1)

ii) In a cracking reaction, reactants are heated to form products. This reaction is endothermic.

On the axes provided, draw the reaction profile of this reaction. Label the energy of the reactants, the energy of the products and the activation energy of the reaction.

(3)

iii) Dodecane, C₁₂H₂₆, can be cracked to form useful products. Complete the equation for the cracking of dodecane by filling in the formula of the single molecule needed to balance the equation.

(1)

C₁₂H₂₆  ....................................... + 3C₂H₄

Fractional distillation is the process by which crude oil is separated into simpler, more useful fractions.

Which of the following statements about the process of fractional distillation is correct?

Most of the fuels used today are obtained from crude oil.

Which statement about crude oil is correct?

Crude oil is separated into several fractions by fractional distillation.

Two of these fractions are kerosene and diesel oil.

i) State a use for each of these fractions.

(2)

kerosene ................................................................

diesel oil .................................................................

ii) Figure 13 shows where the fractions kerosene and diesel oil are produced in the fractionating column.

Figure 13

Kerosene is obtained higher up the column than diesel oil.

Kerosene and diesel oil fractions have slightly different properties.

Choose a property.

State how this property for kerosene compares with the property for diesel oil.

(1)

property ............................................................

comparison .......................................................

Figure 14 shows the formulae of a molecule of butane and of a molecule of pentane.

Butane and pentane are neighbouring members of the same homologous series.

Figure 14

i) Explain, using these formulae, why butane and pentane are neighbouring members of the same homologous series.

(2)

ii) Butane has the formula C₄H₁₀.

Calculate the mass of carbon in 100 g of butane.

Give your answer to three significant figures.

(relative atomic masses: H = 1.00, C = 12.0;
relative formula mass: C₄H₁₀ = 58.0) 

You must show your working.

(3)

iii) Butane burns completely in air to form carbon dioxide and water.

Write the word equation for this reaction.

(2)

Kerosene, bitumen and diesel oil are fractions obtained through the fractional distillation of crude oil.

Which of the following shows the correct use of each fraction? 

Methane is a hydrocarbon fuel.

i) Complete the word equation for the complete combustion of methane in oxygen.

(2)

methane + ................................. → water + ................................

ii) The incomplete combustion of methane can produce carbon and carbon monoxide.

Give the reason why carbon and carbon monoxide are produced in the incomplete combustion of methane.

(1)

Crude oil is a complex mixture of hydrocarbons. Crude oil can be separated into useful fractions by fractional distillation.

Figure 10 shows a fractional distillation column and the fractions produced when crude oil is distilled.

Figure 10

i) Name the fraction in Figure 10 that is used to surface roads.

(1)

ii) Name the fraction in Figure 10 that contains hydrocarbons with the lowest boiling point.

(1)

When crude oil is fractionally distilled, the demand for some fractions is more than the amount produced.

Figure 11 shows the relative amounts of each fraction in a crude oil and the relative demand for each of these fractions.

Figure 11

Which of the following shows the fractions where the relative demand is greater than the relative amount in the crude oil?

Cracking involves the breaking down of large hydrocarbon molecules into smaller hydrocarbon molecules.

i) Octane, C₈ H₁₈, can be cracked to produce one molecule of ethene, C₂H₄, and one molecule of C_xH ₁₄.

C₈H₁₈ → C₂H₄+ C_xH₁₄

Determine the value of x in the molecule of C_xH₁₄.

(1)

x = .........................................

ii) Dodecane is a large hydrocarbon molecule.

When one molecule of dodecane is cracked the products are one molecule of octane and one molecule of butene.

dodecane → octane + butene

Calculate the maximum mass of octane that could be produced when 340 g of dodecane is cracked in this reaction.

(relative formula masses: dodecane = 170, octane = 114)

(2)

mass of octane = ............................................... g

Crude oil is a mixture of hydrocarbons. State what is meant by the term hydrocarbon.

Figure 10 shows a fractionating column used to separate crude oil into fractions.

Figure 10

Describe and explain how fractional distillation separates crude oil into different fractions.

The fractions collected at positions V, W, X and Y in Figure 10 have different viscosities.

Which row correctly identifies the fractions collected at V, W, X and Y in order of increasing viscosity (least viscous to most viscous)?

A sample of one of the fractions is collected. The sample is a very dark, viscous liquid. It is difficult to ignite.

i) Identify the letter of the fraction collected. Give a reason for your answer.

[2]

Fraction: ..........

Reason: ................................................................................

ii) A student makes this hypothesis about Fraction W and Fraction Y:

"Fraction W is a better fuel than Fraction Y because Fraction W has smaller molecules, even though it releases less energy per molecule."

Evaluate the student’s hypothesis.

[2]

Methane, ethane, propane and butane are members of the alkane homologous series. Tridecane is an alkane molecule containing 13 carbon atoms.

Deduce the molecular formula of tridecane. You must show your working.

When fuels are burned in car engines, nitrogen and oxygen from the air react to form oxides of nitrogen.

i) State the condition in car engines that causes this reaction to happen.

[1]

ii) Cars are fitted with a device to remove oxides of nitrogen from their exhaust fumes. State the name of this device.

[1]

Figure 19 shows information about the nitrogen oxides produced by two different vehicle engines.

Figure 19

Give one way in which the data shows that the diesel engine is more damaging to the environment than the petrol engine.

State one disadvantage of using hydrogen, rather than petrol, as a fuel for cars.

The complete combustion of petrol produces carbon dioxide.

Explain how greenhouse gases, such as carbon dioxide, cause the greenhouse effect.

When fuels are burned in car engines, nitrogen and oxygen from the air react to form oxides of nitrogen.

i) State the condition in car engines that causes this reaction to happen.

[1]

ii) Cars are fitted with a device to remove oxides of nitrogen from their exhaust fumes. State the name of this device.

[1]

Figure 5 shows information about the nitrogen oxides produced by two different vehicle engines.

Figure 6

Give one way in which the data shows that the diesel engine is more damaging to the environment than the petrol engine.

State one disadvantage of using hydrogen, rather than petrol, as a fuel for cars.

The complete combustion of petrol produces carbon dioxide.

Explain how greenhouse gases, such as carbon dioxide, cause the greenhouse effect.

A team of aerospace engineers is evaluating a prototype liquid fuel, heptane (C₇​H_16​), for use in a portable heating device.

The engineers test the fuel inside a sealed titanium chamber to measure its energy output.

The heptane used in the prototype is sourced from the petrol fraction of crude oil.

Describe the industrial process used to separate the petrol fraction from crude oil.

The pure heptane prototype fuel is classified as a saturated hydrocarbon.

Which statement explains what is meant by saturated?

The unrefined heptane fuel contains trace amounts of sulfur. When the fuel is burned, the sulfur reacts with oxygen to form sulfur dioxide.

i) Write the balanced chemical equation for this reaction.

[1]

ii) Explain the environmental impact of venting sulfur dioxide gas into the atmosphere.

[3]

The engineers compared heptane, C_7​H₁₆, with dodecane, C₁₂H₂₆.

Figure 11 shows some of their properties. The flash point is the lowest temperature at which a liquid produces enough vapour to ignite.

Figure 11

Use the data in Figure 1 and your knowledge of intermolecular forces to explain why dodecane is harder to ignite than heptane.

To create a fuel blend that ignites more easily, the engineers crack some of the heptane molecules.

Write the balanced equation to show the cracking of one molecule of heptane, C₇​H_16​, to produce one molecule of propene, C₃​H_6​, and one other molecule.

The engineers test the newly cracked fuel mixture with bromine water to confirm that alkenes are present.

What type of chemical reaction occurs when an alkene reacts with bromine?

An impure hydrocarbon fuel is burned in the apparatus in Figure 1.

Figure 1

When the fuel is burned

• the funnel becomes hot

• a colourless liquid forms in tube A

• the indicator in tube B changes colour to show an acidic gas.

Explain these observations.

Higher Only

The energies of some bonds are shown in Figure 2.

Figure 2

Methane burns in oxygen to form carbon dioxide and water. The equation shows the structures of the molecules.

Calculate the energy change, in kJ mol^-1, for this reaction.

energy change = .................................. kJ mol^-1

Petrol and diesel are used as fuels for cars.
The emissions from three similar sized cars were investigated.
The first car was the oldest, had no catalytic converter and used petrol.
The other two cars were only a few years old.
One of these was fitted with a catalytic converter and used petrol and the other car used diesel.

Figure 9 shows the emissions in grams for each kilometre travelled by these three cars.

Figure 3

Discuss and compare the impact on the environment of the emissions from these three cars using the information from Figure 9.

Pentadecane, C₁₅H₃₂, is a hydrocarbon and is used as a fuel.

The incomplete combustion of pentadecane produces carbon monoxide.

 Carbon monoxide is a toxic gas.

i) Explain why the incomplete combustion of pentadecane can produce carbon monoxide as one of the products.

(2)

ii) Explain how carbon monoxide behaves as a toxic gas.

(2)

1 mole of pentadecane can be cracked to form 1 mole of octane, C₈H₁₈, and 1 mole of propene, C₃H₆, and 2 moles of another product.

Complete the balanced equation for this reaction by adding the formula of the missing product.

C₁₅H₃₂ → C₈H₁₈ + C₃H₆ + 2 ..................................

Higher Only

Figure 1 shows the reaction of propene, C₃H₆, with water.

Figure 1

Figure 12 shows some bond energies.

Figure 2

Use the bond energies in Figure 2 to calculate the energy change of the reaction in Figure 1.

energy change of reaction = ................................ kJ mol^-1

Methane gas, CH₄, was burned using the apparatus shown in Figure 3.

Figure 3

Explain why water droplets form on the bottom of the beaker of cold water.

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.

i) Name the process that occurs in reactor 1.

(1)

ii) Explain why this process is carried out.

(2)

Name the reaction that occurs in reactor 2. 

Compare the properties of gasoline and fuel oil.

This question is about pollutants.

Fossil fuels, such as coal, are burned to release energy.

Hydrogen, sulfur, and carbon are all elements found in coal.

Name two products released when coal burns that have a negative effect on the environment.

State the impact each of the products you have named have.

Oxides of nitrogen also impact the environment.

Explain how oxides of nitrogen are formed in car exhausts. 

Describe two effects of oxides of nitrogen being released into the atmosphere.

Hydrogen can be used as an alternative to petrol in cars. 

One method of utilising this is in hydrogen-oxygen fuel cells. 

Write the balanced symbol equation for the overall reaction which occurs in a hydrogen-oxygen fuel cell. 

The General Motors Electrovan was built in 1966. It was the first vehicle powered by a hydrogen fuel cell and could travel at up to 70 mph for 30 seconds.

Suggest two environmental advantages of using a hydrogen fuel cell rather than an internal combustion engine.

Hydrogen fuel cells are commonly considered to be carbon neutral by the general public because they do not release any carbon dioxide or other greenhouse gases when they are used. This is not technically correct.

Suggest why hydrogen fuel cells cannot be classed as carbon neutral.