chemistry : class12 Melting point : Physical properties of haloalkanes : Haloalkanes and Haloarenes MCQ Questions and Answers
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Melting point
MCQ questions and answers.
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MCQ Questions
1. What is meant by the melting point of a haloalkane?
A.
The temperature at which it changes from solid to liquid
B.
The temperature at which it changes from liquid to gas
C.
The temperature at which it decomposes completely
D.
The temperature at which it reacts with water
Correct Answer:
The temperature at which it changes from solid to liquid
Explanation:
The melting point is the temperature at which a haloalkane changes from its solid state to its liquid state.
2. Which factor generally increases the melting point of haloalkanes when the molecular structure remains similar?
A.
Decrease in molecular mass
B.
Increase in molecular mass
C.
Decrease in the number of electrons
D.
Complete removal of the halogen atom
Correct Answer:
Increase in molecular mass
Explanation:
An increase in molecular mass generally strengthens intermolecular attractions, which can raise the melting point of similar haloalkanes.
3. Which haloalkane generally has the highest melting point among the following methyl halides?
A.
Methyl chloride
B.
Methyl bromide
C.
Methyl iodide
D.
Methyl fluoride
Correct Answer:
Methyl iodide
Explanation:
Among these methyl halides, methyl iodide generally has the highest melting point because the iodine atom gives the molecule greater mass and polarizability.
4. Why can two haloalkanes with the same molecular formula have different melting points?
A.
They may have different arrangements of atoms in space
B.
They always contain different elements
C.
Their molecular formulas must be different
D.
They have different numbers of protons in the nucleus
Correct Answer:
They may have different arrangements of atoms in space
Explanation:
Structural or geometric isomers can pack differently in the solid state, so they may have different melting points even when their molecular formulas are the same.
5. Which property of a haloalkane molecule strongly affects its melting point by influencing crystal packing?
A.
Molecular symmetry
B.
Colour of the liquid
C.
Odour of the compound
D.
State of the laboratory glassware
Correct Answer:
Molecular symmetry
Explanation:
More symmetrical molecules often pack more efficiently in crystals, which can result in a higher melting point.
6. Which compound has a higher melting point because of its greater molecular symmetry?
A.
1,2-Dichloroethane
B.
1,1-Dichloroethane
C.
Chloroethane
D.
Bromoethane
Correct Answer:
1,2-Dichloroethane
Explanation:
1,2-Dichloroethane has a more symmetrical arrangement of chlorine atoms than 1,1-dichloroethane, allowing more efficient crystal packing and a higher melting point.
7. The melting point of a haloalkane mainly depends on the balance between intermolecular forces and what other factor?
A.
Crystal packing
B.
Colour intensity
C.
Volume of the container
D.
Atmospheric oxygen content
Correct Answer:
Crystal packing
Explanation:
Melting points depend on the strength of intermolecular attractions and how efficiently molecules are arranged in the solid crystal.
8. Which statement about branching and the melting point of haloalkanes is correct?
A.
Branching always makes the melting point lower
B.
Branching always makes the melting point higher
C.
Branching can change the melting point by changing molecular packing
D.
Branching has no effect on melting point
Correct Answer:
Branching can change the melting point by changing molecular packing
Explanation:
Branching changes the shape and symmetry of a molecule, which can alter how well molecules pack in the solid state and therefore change the melting point.
9. Which of the following haloalkanes has the highest melting point?
A.
Chloromethane
B.
Bromomethane
C.
Iodomethane
D.
Fluoromethane
Correct Answer:
Iodomethane
Explanation:
Iodomethane has the highest melting point among the listed methyl halides because its iodine atom gives the molecule greater polarizability and stronger dispersion forces.
10. A haloalkane with a highly symmetrical structure is likely to have a relatively high melting point because its molecules:
A.
Pack efficiently in the solid state
B.
Have no intermolecular forces
C.
Are always ionic
D.
Cannot form a crystal
Correct Answer:
Pack efficiently in the solid state
Explanation:
High symmetry usually allows molecules to arrange more regularly and closely in a crystal lattice, increasing the melting point.
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