CIE iGCSE Co-Ordinated Science C11.5 Alkenes Exam Style Questions Paper 1
Question
Which statement about ethene, C₂H₄, is not correct?
A. It is an unsaturated hydrocarbon.
B. It is produced by cracking.
C. It is used to make a polymer.
D. It turns aqueous bromine brown.
▶️Answer/Explanation
Answer: D. It turns aqueous bromine brown.
Explanation: Ethene is an unsaturated hydrocarbon (A), produced by cracking (B), and used to make polymers like polyethylene (C). However, it decolorizes aqueous bromine (turns it from brown to colorless), so statement D is incorrect.
Question
Which process produces alkenes from alkanes?
A) combustion
B) cracking
C) oxidation
D) reduction
▶️Answer/Explanation
Answer: B) cracking
Explanation: Cracking is a process that breaks down larger alkane molecules into smaller alkenes and alkanes.
Question
Which substance rapidly decolourises aqueous bromine?
A ethane
B ethanol
C ethene
D poly(ethene)
▶️Answer/Explanation
Answer: C ethene
Explanation: Ethene (C2H4) is an unsaturated hydrocarbon that reacts with bromine, causing the bromine solution to decolourise. This is a test for unsaturation in hydrocarbons.
Question
Which substance is an unsaturated compound?
A ethane
B ethanol
C ethene
D methane
▶️Answer/Explanation
Ans : C
Question
Which diagram represents a molecule that is formed by fermentation?
▶️Answer/Explanation
Ans : D
Question
Molecules of ethene react together to form long chain molecules.
What is the name of this type of reaction?
(A) addition polymerisation
(B) cracking
(C) fermentation
(D) thermal decomposition
▶️Answer/Explanation
Ans: A
Question
Which substance reacts with ethene to produce ethanol?
(A) bromine
(B) hydrogen
(C) oxygen
(D) steam
▶Answer/Explanation
Ans : D
Question
Which molecule reacts with aqueous bromine?
▶️Answer/Explanation
Ans: B
Question
Ethene is produced when decane, a large hydrocarbon, is heated with a catalyst. What is the name of this process?
A. combustion
B. cracking
C. displacement
D. neutralisation
▶️Answer/Explanation
Answer: B
Explanation: The process of breaking down large hydrocarbons into smaller ones, such as ethene, by heating with a catalyst is called cracking.
Question
The flow diagram shows the manufacture of ethanol from alkanes.
What are process X and reagent Y?
| process X | reagent Y | |
|---|---|---|
| A | cracking | hydrogen |
| B | cracking | steam |
| C | fractional distillation | hydrogen |
| D | fractional distillation | steam |
▶️Answer/Explanation
Answer: B
Explanation: Ethanol can be produced from alkanes through cracking (process X) and then reacting the resulting alkenes with steam (reagent Y) in the presence of a catalyst.