Petroleum is a useful natural resource.
The diagram shows how petroleum can be separated into useful substances.
(a) What is the name of the separation process shown in the diagram?
(b) Name the fraction leaving at:
A
B
(c) Refinery gas is a mixture of hydrocarbons.
One refinery gas is butane, \(C_4H_{10}\).
(i) Suggest the names of two other refinery gases.
(ii) Write the chemical equation for the complete combustion of butane.
(iii) Name the toxic gas produced by the incomplete combustion of butane.
(d) Gasoline and kerosene are both fuels. They have different properties.
(i) Describe the differences in the properties given.
viscosity of the fuel
flammability of the fuel
(ii) What difference in the molecules of gasoline and kerosene causes these differences in properties?
(e) Hydrogen fuel cells can be used to power vehicles.
Write the word equation for the overall reaction that takes place in a hydrogen fuel cell.
▶️ Answer/Explanation
(a) The separation process is fractional distillation.
Explanation: Petroleum is heated, and its components are separated based on their boiling points in a fractionating column.
(b) Fractions:
– A: Naphtha (used in petrochemical industry).
– B: Bitumen (used for road surfacing).
(c) (i) Other refinery gases: methane (CH4) and propane (C3H8).
(ii) Complete combustion of butane:
\[ 2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O \]
(iii) Toxic gas from incomplete combustion: carbon monoxide (CO).
(d) (i) Property differences:
– Viscosity: Kerosene is more viscous (flows less easily) than gasoline.
– Flammability: Gasoline is more flammable (ignites more easily) than kerosene.
(ii) Molecular difference: Kerosene has longer hydrocarbon chains (C12-C16) compared to gasoline (C5-C10), affecting intermolecular forces.
(e) Hydrogen fuel cell reaction:
hydrogen + oxygen → water
Note: The actual chemical equation is \(2H_2 + O_2 \rightarrow 2H_2O\).
Biogas is made by fermenting animal and vegetable waste.
(a) The table shows the percentage composition of the gases present in a sample of biogas.
Deduce the percentage of nitrogen present in this sample of biogas.
(b)(i) Balance the chemical equation for the complete combustion of methane.
\( \text{CH}_4 + \_\_ \text{O}_2 \rightarrow \text{CO}_2 + \_\_ \text{H}_2\text{O} \)
(b)(ii) Which one of these compounds belongs to the same homologous series as methane?
Draw a circle around the correct answer.
methanoic acid methanol propane propanol propene
(b)(iii) Methane is present in the refinery gas fraction produced by the fractional distillation of petroleum.
Match the fractions on the left with their uses on the right.
(c)(i) Draw a dot-and-cross diagram to show the electron arrangement in a molecule of hydrogen.
(c)(ii) State one use of hydrogen.
(d) The biogas contains a small amount of compound C. The structure of compound C is shown.
(i) On the structure shown, draw a circle around the carboxylic acid functional group.
(ii) How many different types of atoms are present in compound C?
(e) Describe the manufacture of ethanol by fermentation. In your answer include:
– the names of the substances needed for fermentation
– the conditions needed for fermentation.
▶️ Answer/Explanation
(a) Percentage of nitrogen = 100% – (64% + 30%) = 6%.
(b)(i) Balanced equation: \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \).
(b)(ii) Propane (both methane and propane are alkanes).
(b)(iii) Correct matches:
– Fuel oil → Fuel for ships
– Bitumen → Making roads
– Naphtha → Making chemicals
(c)(i) Hydrogen molecule (H2) dot-and-cross diagram:
H • • H (shared pair of electrons between two H atoms).
(c)(ii) Use of hydrogen: Fuel for rockets or manufacture of ammonia.
(d)(i) Circle the -COOH group in the structure.
(d)(ii) Compound C contains 5 types of atoms (C, H, O, N, S).
(e) Ethanol production by fermentation:
Substances needed: Glucose/sugar + yeast.
Conditions:
1. Anaerobic (no oxygen)
2. Temperature 25–30°C
3. Neutral pH
4. Aqueous solution