Home / iGCSE Chemistry (0620) Core:11.5 Alkenes: Exam Style Questions Paper 1

iGCSE Chemistry (0620) Core:11.5 Alkenes: Exam Style Questions Paper 1

iGCSE Chemistry (0620) Core Paper 1 - All Chapters
Question

The formulae of two organic compounds, P and Q, are shown.

Which type of organic compounds are P and Q?

 PQ
Aalcoholalkane
Balcoholalkene
Ccarboxylic acidalkane
Dcarboxylic acidalkene
▶️ Answer/Explanation
Solution

Ans: B

Let’s analyze both compounds:

For P (CH3CH2CH2OH):
This compound has an -OH functional group attached to a carbon chain, which is the characteristic feature of an alcohol. It’s specifically propan-1-ol.

For Q (CH3CH=CHCH3):
This compound contains a carbon-carbon double bond (C=C), which is the defining feature of an alkene. It’s specifically but-2-ene.

Looking at the options:
Option B correctly identifies P as an alcohol and Q as an alkene, which matches our analysis.

Question

A hydrocarbon decolourises bromine water.

Which statement about the hydrocarbon is correct?

A) It is an alkane.
B) Its molecular formula is \( C_2H_6 \).
C) It is a saturated hydrocarbon.
D) It has the general formula \( C_nH_{2n} \).

▶️ Answer/Explanation
Solution

Ans: D

The key information here is that the hydrocarbon decolourises bromine water. This is a characteristic reaction of unsaturated hydrocarbons (alkenes) which can undergo addition reactions with bromine. Alkanes (option A) are saturated and don’t react with bromine water. Option B describes ethane which is an alkane. Option C is incorrect because saturated hydrocarbons don’t decolourise bromine water. Option D is correct because alkenes have the general formula \( C_nH_{2n} \) and react with bromine water.

Question

Ethene and propene are both members of the same homologous series. Which statements explain why ethene and propene have similar chemical properties?
                 1         They are both hydrocarbons.
                 2         They are both made by cracking.
                 3         They have the same functional group.
A. 1 and 2                   B. 1 and 3                      C. 2 only                   D. 3 only

▶️Answer/Explanation

Ans:

D

Both ethene and propene are both members of the alkene group. Hence, they have the same functional group. So, ethene and propene have similar chemical properties.

Question

Increasing the number of atoms in one molecule of a hydrocarbon increases the amount of
energy released when it burns.
What is the correct order?

▶️Answer/Explanation

Ans:D

Methane CH4 has 4 atoms, 

Ethene, C2H4 has 6 atoms and 

Ethane, C2H6 has 9 atoms. 

As increasing the number of atoms in one molecule of a hydrocarbon increases the amount of energy released when it burns, hence methane releases least energy and ethane releases the maximum energy.

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