chemistry : class12 Branching effect : Physical properties of haloalkanes : Haloalkanes and Haloarenes MCQ Questions and Answers
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Branching effect
MCQ questions and answers.
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MCQ Questions
1. For isomeric haloalkanes having the same molecular formula, what is the usual effect of increased branching on boiling point?
A.
It usually increases the boiling point
B.
It usually decreases the boiling point
C.
It always makes the boiling point equal to the melting point
D.
It has no effect on the boiling point
Correct Answer:
It usually decreases the boiling point
Explanation:
Branching decreases the surface area of a haloalkane molecule, weakening intermolecular van der Waals forces and usually lowering its boiling point.
2. Which isomer of chlorobutane generally has the lowest boiling point because of maximum branching?
A.
n-Butyl chloride
B.
sec-Butyl chloride
C.
Isobutyl chloride
D.
tert-Butyl chloride
Correct Answer:
tert-Butyl chloride
Explanation:
tert-Butyl chloride is the most highly branched chlorobutane isomer, so it has the smallest effective surface area and generally the lowest boiling point.
3. Why does branching generally lower the boiling point of isomeric haloalkanes?
A.
It increases the molecular mass
B.
It decreases the strength of intermolecular attractions
C.
It increases the number of halogen atoms
D.
It changes the haloalkane into an ionic compound
Correct Answer:
It decreases the strength of intermolecular attractions
Explanation:
Branching makes molecules more compact and reduces their area of contact, thereby weakening intermolecular van der Waals attractions.
4. Among the following isomeric compounds, which one is expected to have the highest boiling point?
A.
1-Chlorobutane
B.
2-Chlorobutane
C.
1-Chloro-2-methylpropane
D.
2-Chloro-2-methylpropane
Correct Answer:
1-Chlorobutane
Explanation:
1-Chlorobutane has an unbranched chain and the largest effective surface area among these isomers, giving stronger intermolecular attractions and a higher boiling point.
5. As branching increases in a series of isomeric haloalkanes, the molecules generally become:
A.
Less compact and more elongated
B.
More compact and less elongated
C.
More ionic
D.
Heavier because of extra carbon atoms
Correct Answer:
More compact and less elongated
Explanation:
Branching causes the carbon chain to fold into a more compact shape, reducing the molecular surface available for intermolecular contact.
6. Which physical property of isomeric haloalkanes is most directly explained by the decrease in surface area caused by branching?
A.
Boiling point
B.
Number of carbon atoms
C.
Molecular formula
D.
Number of halogen atoms
Correct Answer:
Boiling point
Explanation:
A smaller surface area reduces van der Waals attractions between molecules, so branching generally causes a decrease in boiling point.
7. For haloalkanes with the same molecular formula and halogen atom, which structure generally has the lowest boiling point?
A.
The least branched structure
B.
The straight-chain structure
C.
The most highly branched structure
D.
The structure with the longest exposed surface
Correct Answer:
The most highly branched structure
Explanation:
Greater branching produces a more compact molecule with less surface contact, so intermolecular attractions and boiling point generally decrease.
8. Compared with its straight-chain isomer, a branched haloalkane usually has weaker:
A.
C–X covalent bonds
B.
Intermolecular van der Waals forces
C.
Carbon-carbon sigma bonds
D.
Nuclear forces
Correct Answer:
Intermolecular van der Waals forces
Explanation:
Branching reduces the contact area between molecules, weakening intermolecular van der Waals forces compared with the straight-chain isomer.
9. Which order generally represents the boiling points of isomeric butyl chlorides from highest to lowest?
Explanation:
The boiling point generally decreases as branching increases. n-Butyl chloride is least branched, while tert-butyl chloride is most branched.
10. What happens to the effective surface area of a haloalkane molecule when branching is introduced without changing its molecular formula?
A.
It generally decreases
B.
It generally increases greatly
C.
It becomes zero
D.
It becomes equal to the molecular mass
Correct Answer:
It generally decreases
Explanation:
Branching makes the molecule more compact, reducing its effective surface area and consequently lowering intermolecular attractions and usually its boiling point.
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