Organic Chemistry - Alkanes and Alkenes Practice Questions
A-Levels · A-Level Chemistry · 141 free MCQs with instant results and detailed explanations.
141
Total
39
Easy
74
Medium
28
Hard
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Sample Questions from Organic Chemistry - Alkanes and Alkenes
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Q1
Easy
Which of the following is a characteristic property of alkanes?
A.
They are highly reactive with bromine in dark.
B.
They have a general formula of CnH2n+2.
C.
They can form double bonds.
D.
They are soluble in water.
Show Answer & Explanation
Correct Answer: B
Alkanes follow the general formula CnH2n+2, where 'n' is the number of carbon atoms. This formula indicates that for every carbon, there are two hydrogens plus two for the ends. This is a defining characteristic of alkanes.
Q2
Easy
What is the primary product when ethene is added to hydrogen in the presence of a catalyst?
A.
Ethanol
B.
Ethane
C.
Ethylene oxide
D.
Propane
Show Answer & Explanation
Correct Answer: B
The addition of hydrogen to ethene (an alkene) in the presence of a catalyst (such as palladium or platinum) results in the formation of ethane, which is a saturated hydrocarbon. This reaction is known as hydrogenation.
Q3
Easy
Which of the following compounds is an alkene?
A.
C3H8
B.
C4H10
C.
C2H4
D.
C5H12
Show Answer & Explanation
Correct Answer: C
C2H4 is an alkene because it has a carbon-carbon double bond, fitting the general formula CnH2n (n=2). In contrast, the other options are alkanes, which have single bonds and follow the formula CnH2n+2.
Q4
Medium
What is the major product when 1-butene undergoes hydroboration-oxidation?
A.
1-butanol
B.
2-butanol
C.
butanal
D.
butan-2-one
Show Answer & Explanation
Correct Answer: B
The hydroboration-oxidation of 1-butene yields 2-butanol as the major product due to the anti-Markovnikov addition of water, leading to the formation of the secondary alcohol.
Q5
Medium
What is the expected product of the reaction between ethylene and bromine?
A.
Bromoethane
B.
Dibromoethane
C.
1-bromoethane
D.
Bromoethane and Ethane
Show Answer & Explanation
Correct Answer: B
The reaction of ethylene (an alkene) with bromine results in the formation of dibromoethane through an electrophilic addition mechanism, adding bromine across the double bond.
Q6
Medium
What type of isomerism is exhibited by but-2-ene?
A.
Structural isomerism
B.
Geometric isomerism
C.
Optical isomerism
D.
Tautomeric isomerism
Show Answer & Explanation
Correct Answer: B
But-2-ene exhibits geometric isomerism (cis-trans isomerism) due to the restricted rotation around the carbon-carbon double bond, allowing for different spatial arrangements.
Q7
Medium
Which reagent would you use to convert cyclohexene to cyclohexanol?
A.
H2 with a catalyst
B.
Br2
C.
H2O in the presence of an acid
D.
KMnO4
Show Answer & Explanation
Correct Answer: C
Cyclohexene can be converted to cyclohexanol via hydration using water in the presence of an acid, which facilitates the addition of water across the double bond.
Q8
Hard
Which of the following reactions will result in the formation of an alkene from an alkane?
A.
Electrophilic addition of HBr to an alkene
B.
Dehydrogenation of an alkane
C.
Hydration of an alkene
D.
Hydrogenation of an alkene
Show Answer & Explanation
Correct Answer: B
Dehydrogenation of an alkane involves the removal of hydrogen atoms, leading to the formation of an alkene. This reaction typically requires heat and a catalyst.
Q9
Hard
When propene is reacted with excess bromine in a non-polar solvent, what is the main product formed?
A.
1,2-dibromopropane
B.
Bromopropane
C.
Propane
D.
2-bromopropane
Show Answer & Explanation
Correct Answer: A
The reaction of propene with excess bromine results in the addition of bromine across the double bond, forming 1,2-dibromopropane as the main product.
Q10
Hard
What is the major product of the reaction between 2-butene and hydrogen bromide in the presence of peroxide?
A.
1-bromo-2-butene
B.
2-bromo-2-butane
C.
2-bromo-1-butene
D.
1-bromo-1-butene
Show Answer & Explanation
Correct Answer: C
The presence of peroxides leads to a free radical mechanism where the HBr adds to the double bond in a manner that produces 2-bromo-1-butene, following anti-Markovnikov's rule.
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Organic Chemistry - Alkanes and Alkenes — A-Levels A-Level Chemistry Practice Questions Online
This page contains 141 practice MCQs for the chapter Organic Chemistry - Alkanes and Alkenes in A-Levels A-Level Chemistry. The questions are organized by difficulty — 39 easy, 74 medium, 28 hard — so you can choose the right level for your preparation.
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