Coal gas is made by heating coal in the absence of air. The list shows the main gases present in coal gas:
- carbon dioxide
- carbon monoxide
- ethene
- hydrogen
- methane
- nitrogen
(a) (i) Which one of these gases is an alkane? [1]
(ii) Draw the structure of a molecule of ethene. Show all of the atoms and all of the bonds. [1]
(iii) Describe how aqueous bromine can be used to tell the difference between methane and ethene. [2]
(b) Ethene molecules react with each other to form poly(ethene).
(i) What is the name given to this type of chemical reaction? [1]
(ii) Which one of the following words describes the ethene molecules in this reaction?
(elements, mixtures, monomers, polymers) [1]
(iii) Poly(ethene) is a non-biodegradable plastic. What is meant by the term non-biodegradable? [1]
(iv) Describe one pollution problem caused by non-biodegradable plastics. [1]
(c) Ethanol can be made from ethene and one other reactant.
• Name the other reactant.
• State the conditions needed to make ethanol from ethene. [3]
▶️ Answer/Explanation
(a)(i) Ans: methane
Methane (CH₄) is the only alkane in the list, as alkanes are saturated hydrocarbons with single bonds.
(a)(ii) Ans: Ethene structure (C₂H₄)
Ethene has a double bond between two carbon atoms, with each carbon bonded to two hydrogen atoms.
(a)(iii) Ans: Bromine water test
• Methane: No reaction – bromine water remains orange.
• Ethene: Decolorizes bromine water as it undergoes addition reaction at the double bond.
(b)(i) Ans: Polymerization (or addition polymerization)
Ethene monomers join together through their double bonds to form the polymer poly(ethene).
(b)(ii) Ans: monomers
Ethene molecules are the repeating units (monomers) that combine to form the polymer.
(b)(iii) Ans: Cannot be broken down by natural processes
Non-biodegradable materials persist in the environment as they resist decomposition by microorganisms.
(b)(iv) Ans: Wildlife hazards or landfill accumulation
Plastic waste can entangle animals or block digestive systems if ingested, and accumulates in landfills.
(c) Ans: Steam with phosphoric acid catalyst at 300°C/60 atm
• Reactant: Steam (H₂O)
• Conditions: High temperature (~300°C), pressure (60 atm), and phosphoric acid catalyst.
Reaction: \(C_2H_4 + H_2O \rightarrow C_2H_5OH\)
The structure of malic acid is shown.
(a)(i) On the structure draw a circle around the alcohol functional group.
(a)(ii) Deduce the formula of malic acid to show the number of carbon, hydrogen and oxygen atoms.
(b) When malic acid is heated it forms compound F.
The structure of compound F is shown.
Explain why compound F is described as unsaturated.
(c) Compound F can form polymers.
(i) State the meaning of the term polymer.
(ii) State the name of the polymer formed when ethene is polymerised.
(d) Ethanoic acid is a carboxylic acid.
Describe the observations made when dilute ethanoic acid reacts with:
magnesium
litmus solution.
(e) The graph shows how the pH changes when dilute ethanoic acid is added slowly to aqueous sodium hydroxide.
(i) Deduce the pH of the aqueous sodium hydroxide before the addition of dilute ethanoic acid.
(ii) Deduce the volume of dilute ethanoic acid added when the pH is neutral.
▶️ Answer/Explanation
(a)(i) Ans: OH alcohol group circled
The alcohol functional group (-OH) is circled on the malic acid structure, which is attached to a carbon atom.
(a)(ii) Ans: \(C_4H_6O_5\)
Counting the atoms in the malic acid structure: 4 carbon (C), 6 hydrogen (H), and 5 oxygen (O) atoms.
(b) Ans: It has a C=C double bond
Compound F is unsaturated because it contains a carbon-carbon double bond (C=C), which is characteristic of unsaturated compounds.
(c)(i) Ans: Large molecules built up from small repeating units (monomers)
Polymers are macromolecules formed by the repeated linking of small monomer units through chemical bonds.
(c)(ii) Ans: Poly(ethene)
When ethene monomers polymerize, they form poly(ethene), commonly known as polyethylene.
(d) Ans: With Mg – fizzes/bubbles; litmus – turns red/pink
Ethanoic acid reacts with magnesium to produce hydrogen gas (fizzing) and turns litmus red due to its acidic nature.
(e)(i) Ans: pH 13
The initial pH of sodium hydroxide solution is strongly basic, read from the graph’s y-intercept as 13.
(e)(ii) Ans: 18 \(cm^3\)
Neutralization occurs at pH 7, corresponding to 18 \(cm^3\) of ethanoic acid added, where the curve crosses the neutral point.