Science (086) — AI-generated practice question

(i) Electron dot structure of ethyne (C₂H₂):

$$\text{H} :\!\!\overset{..}{\text{C}}\!\!:\!\!:\!\!:\!\!\overset{..}{\text{C}}\!\!: \text{H}$$

H — C ≡ C — H (with each C sharing 3 pairs of electrons, forming a triple bond, and one bond each with H)

(ii) Ethyne is an unsaturated compound because it contains a triple bond between the two carbon atoms. Compounds with double or triple bonds between carbon atoms are called unsaturated carbon compounds.

(iii)

$$\text{C}_2\text{H}_2 + 2\text{H}_2 \xrightarrow{\text{Ni}} \text{C}_2\text{H}_6$$

The product formed is ethane.

Source: Chapter 4, Section 4.2.1 — Saturated and Unsaturated Carbon Compounds

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• For (i), show the triple bond clearly — three pairs of shared electrons between the two C atoms, with one H on each end. Examiners award marks for correct depiction of the triple bond.
• For (ii), one line identifying it as unsaturated + one reason (triple bond) is sufficient for 1 mark.
• For (iii), balance the equation correctly: ethyne needs 2 moles of H₂ (since it has a triple bond, two bonds must be broken and hydrogenated). Naming the product (ethane) is essential — don't skip it.