Hydrocarbons: Fuel & Feedstock (AQA GCSE Chemistry)

Crude oil is a fossil fuel and is extracted from below the Earth's surface.

It contains many useful substances which are separated into fractions before further processing. 

Describe the process of separation of crude oil in as much detail as possible.

Often long chain alkanes are produced from the fractional distillation of crude oil.

These then undergo a process called cracking to produce other compounds.

Explain why this is done and include the products of cracking in your answer.

Decane is an example of a long chain alkane extracted from crude oil.

It is a long chain hydrocarbon that contains 10 carbon atoms.

Complete the equation for the cracking of decane by writing the correct formula and the name of the third product. 

C₁₀H₂₂  →   C₅H₁₀    +   C₃H₈   +   _______

Pentene is used to produce the polymer poly(pentene). 

Complete the equation for this process and draw the displayed structure of poly(pentene) in Figure 1.

Figure 1

The table displays information about the formula mass and boiling point of some alkanes.

Give the formula of and name of the compound that is missing.

Describe the relationship between the relative formula mass and boiling point.

Plot the points from the table on Figure 2 and draw a best fit line.

Figure 2

Use the graph to determine the boiling point of butane, showing clearly how you arrived at your answer.

Heptane is an alkane with seven carbons.

What is the chemical formula of heptane?

The complete combustion of pentane, C₅H₁₂, takes place in the following unbalanced equation:

_C₅H₁₂   +   _O₂ →   _CO₂   +  _H₂O

What numbers will balance the reaction?

Crude oil can be separated into different fractions which contain molecules with a similar number of carbon atoms.

These fractions undergo further processing to produce fuels and feedstock for the petrochemical industry.

State two fuels that are obtained from crude oil.

Fractions from crude oil can also be processed to produce feedstock for the petrochemical industry.

Many of the materials we use in everyday life are produced by the petrochemical industry.

State two useful substances that are produced by the petrochemical industry.

Figure 1 shows the percentage by mass of different fractions in a sample of crude oil.

Figure 1

Calculate the mass of diesel oil that can be obtained from 5000 kg of crude oil.

What mass of crude oil is needed to obtain 5700 kg of petrol?

Saturated hydrocarbons are fuels.

Write down the balanced equation for the complete combustion of propane, C₃H₈.

_____   +  _____    →   _____   +   _____

Naphtha is a fraction obtained from crude oil with the formula C₇H₁₆.

Draw the displayed formula of naphtha.

Hexadecane, C₁₆H₃₄, is also another hydrocarbon that can be obtained from crude oil.

How would you expect the boiling point of hexadecane to differ from the boiling point of naphtha?

Explain your answer.

Which molecule can be cracked to produce hexane, C₆H₁₄?

Which of the following is true about the properties of hydrocarbons and increasing molecular size? 

Poly(ethene) is a long-chain saturated hydrocarbon with many applications. The formula for part of the polymer chain is shown in Figure 1.

Figure 1

Write down the molecular formula of the small molecule from which poly(ethene) is made.

Describe how poly(ethene) is formed. 

You do not need to give the names of catalysts or reaction conditions.

Many polymers are produced from alkenes. Alkenes are obtained during cracking.

When the alkane, C₁₄H₃₀, undergoes cracking, it can form a shorter chain alkane and butene.

Give the formula of the shorter chain alkane that is produced.

Alkanes are a group of compounds that form a homologous series.

State two characteristics of a homologous series.

Most hydrocarbons extracted from crude oil are alkanes.

Long chain alkanes are routinely cracked to produce more useful molecules.

The equation shows the cracking of dodecane.

C₁₂H₂₆ → C₄H₁₀ + C₆H₁₂ + C₂H₄

Give two conditions necessary to crack large alkane molecules.

State whether C₁₂H₂₆ has a higher boiling point than C₆H₁₂ and explain why.

Two of the products formed in the reaction in part (a) are alkenes.

Describe the colour change you would see when bromine water is added to an alkene.

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 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.

Short chain fractions have low supply and high market demand.

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

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.

This question is about the reactions of alkanes.

Decane can be cracked to form heptane and one other product in the following reaction:

C₁₀H₂₂   →   C₇H₁₆   + ____________

Name and draw the displayed formula of the other product formed.

Describe and give the result of a chemical test that would distinguish between the two products.

Describe how catalytic cracking is carried out.

Explain why decane is a saturated hydrocarbon.

Another alkane, butane, can undergo the following combustion reactions:

   Equation 1:  2C₄H₁₀ + 13O₂ ⟶ 8CO₂ + 10H₂O 

   Equation 2:     2C₄H₁₀ + 5O₂ ⟶ 8C + 10H₂O 

Explain why different products are made.

This question is about crude oil and the hydrocarbons obtained from it. 

Describe how crude oil is formed.

Table 1 shows some alkanes that are found in crude oil. 

Table 1 

What is the general formula for alkanes?

Write the balanced symbol equation for the complete combustion of C₇H₁₆. 

Explain the trend in boiling points of the alkanes.

A student was investigating the properties of the alkanes shown in Table 1 in part (a) using the following method:

1) Pour 20 cm³ of C₅H₁₂ into a funnel 

2) Open the tap and start a stopwatch 

3) When the level of C₅H₁₂ reaches line X stop the stopwatch 

4) Repeat steps with the other two alkanes 

The diagram in Figure 1 shows the apparatus used.

Figure 1

C₅H₁₂ took 5.3 seconds to reach line X.

Explain the trend you would expect to see when the student repeats the method with the other two alkanes.