CIE iGCSE Co-Ordinated Science C11.5 Alkenes Exam Style Questions Paper 2
▶️ Answer/Explanation
Ethene reacts with steam (water) to produce ethanol in an addition reaction. In this process, the double bond between the two carbon atoms in ethene breaks, and hydrogen and oxygen atoms from steam are added across the double bond. This type of reaction is known as addition because atoms are added to the unsaturated molecule without removing anything.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
X does not decolourise bromine water, so it is a saturated alkane; with 2 carbons this is ethane, \(C_2H_6\).
Y decolourises bromine water, so it is an unsaturated alkene; with 3 carbons this is propene, \(C_3H_6\).
Comparing hydrogen atoms: X has 6 and Y has 6, so the difference is \(6 – 6 = 0\).
✅ Answer: (A)
Y decolourises bromine water, so it is an unsaturated alkene; with 3 carbons this is propene, \(C_3H_6\).
Comparing hydrogen atoms: X has 6 and Y has 6, so the difference is \(6 – 6 = 0\).
✅ Answer: (A)
▶️ Answer/Explanation
\( CH_3CHCH_2 \) is propene, which contains a carbon–carbon double bond, so it belongs to the alkene homologous series, not the alkane series.
Alkenes have the general formula \( C_nH_{2n} \), since they have two fewer hydrogen atoms than the corresponding alkane due to the double bond.
This matches row D; the alkane formula \( C_nH_{2n+2} \) in rows A and C would apply to a saturated hydrocarbon instead.
✅ Answer: (D)
Alkenes have the general formula \( C_nH_{2n} \), since they have two fewer hydrogen atoms than the corresponding alkane due to the double bond.
This matches row D; the alkane formula \( C_nH_{2n+2} \) in rows A and C would apply to a saturated hydrocarbon instead.
✅ Answer: (D)
▶️ Answer/Explanation
Both ethene and but-1-ene are alkenes formed by cracking larger alkane molecules, so statement 2 is correct.
As alkenes with a C=C double bond, both add steam to form the corresponding alcohol, so statement 3 is also correct; both share the same general formula (C_nH_{2n}), and both decolourise bromine water, so statements 1 and 4 are false.
✅ Answer: (C)
As alkenes with a C=C double bond, both add steam to form the corresponding alcohol, so statement 3 is also correct; both share the same general formula (C_nH_{2n}), and both decolourise bromine water, so statements 1 and 4 are false.
✅ Answer: (C)
▶️ Answer/Explanation
Ethene reacts with hydrogen to form ethane (hydrogenation). Addition reactions only produce one product because the double bond opens to add atoms. Ethene is unsaturated, not saturated. Reaction with steam forms ethanol, not ethane.
✅ Answer: (B)
✅ Answer: (B)