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