Question

1. the following shows some properties of two hydrocarbons x and y.

• x decolourises aqueous bromine in the dark while y does not.
• x has a higher boiling point than y.
• a larger volume of carbon dioxide is produced from the combustion of x than y.

what could be x and y?
\

$$\begin{array}{|c|c|c|} \\hline & x & y \\\\ \\hline a & \\text{ethane} & \\text{propane} \\\\ b & \\text{ethene} & \\text{propene} \\\\ c & \\text{propane} & \\text{ethene} \\\\ d & \\text{propene} & \\text{ethane} \\\\ \\hline \\end{array}$$

1. margarine is manufactured industrially from hydrogenation of vegetable oil under catalysed conditions. which statement about the chemical structures of vegetable oil and margarine is correct?

a both are saturated hydrocarbons.
b the boiling point of vegetable oil is higher.
c both are naturally occurring compounds.
d vegetable oil is a liquid while margarine is a solid at room temperature.

1. the alkene, 2-methylpropene, \\(c_4h_8\\), is a monomer used in the production of synthetic rubber. its structural formula is shown below.

which of the following substances is not likely to react with the alkene through addition?
a oxygen
b iodine
c hydrogen chloride
d steam

Explanation:

Analyze Question 26

• Property 1: \(X\) decolourises aqueous bromine in the dark, so \(X\) is an unsaturated hydrocarbon (alkene). \(Y\) does not, so \(Y\) is a saturated hydrocarbon (alkane).
• Property 2: \(X\) has a higher boiling point than \(Y\), meaning \(X\) has a larger molecular size/mass than \(Y\).
• Property 3: A larger volume of \(\text{CO}_2\) is produced from the combustion of \(X\) than \(Y\), confirming \(X\) contains more carbon atoms per molecule than \(Y\).
• Evaluating options:
• (A) \(X\) is ethane (alkane), \(Y\) is propane (alkane) — Incorrect.
• (B) \(X\) is ethene (alkene, 2 carbons), \(Y\) is propene (alkene, 3 carbons) — Incorrect.
• (C) \(X\) is propane (alkane, 3 carbons), \(Y\) is ethene (alkene, 2 carbons) — Incorrect.
• (D) \(X\) is propene (alkene, 3 carbons), \(Y\) is ethane (alkane, 2 carbons) — Correct.

Analyze Question 27

• Vegetable oil contains unsaturated fatty acid chains (liquid at room temperature).
• Hydrogenation converts unsaturated carbon-carbon double bonds into saturated single bonds, raising the melting point to make margarine a solid/semi-solid at room temperature.
• Evaluating options:
• (A) Both are saturated hydrocarbons — Incorrect (they are esters/triglycerides, not hydrocarbons).
• (B) The boiling point of vegetable oil is higher — Incorrect.
• (C) Both are naturally occurring compounds — Incorrect (margarine is synthetic/manufactured).
• (D) Vegetable oil is a liquid while margarine is a solid at room temperature — Correct.

Analyze Question 28

• Alkenes undergo addition reactions across the \(\text{C}=\text{C}\) double bond with halogens (iodine), hydrogen halides (hydrogen chloride), and steam (water).
• Combustion with oxygen is an oxidation/combustion reaction, not an addition reaction.
• Evaluating options:
• (A) oxygen — Correct (does not react through addition).
• (B) iodine — Incorrect (undergoes addition).
• (C) hydrogen chloride — Incorrect (undergoes addition).
• (D) steam — Incorrect (undergoes addition).

Answer:

Question 26

• (A) X: ethane, Y: propane
• (B) X: ethene, Y: propene
• (C) X: propane, Y: ethene
• (D) X: propene, Y: ethane (Correct answer)

Question 27

• (A) Both are saturated hydrocarbons.
• (B) The boiling point of vegetable oil is higher.
• (C) Both are naturally occurring compounds.
• (D) Vegetable oil is a liquid while margarine is a solid at room temperature. (Correct answer)

Question 28

• (A) oxygen (Correct answer)
• (B) iodine
• (C) hydrogen chloride
• (D) steam