# Chemistry Questions and Answers – Haloarenes Physical Properties

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This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Haloarenes Physical Properties”.

1. Which of the following haloalkanes exist as liquids at room temperature?
a) Methyl chloride
b) Methyl bromide
c) Ethyl chloride
d) Propyl bromide

Explanation: The lower members like methyl chloride, methyl bromide and ethyl chloride exist as gases at room temperature. The higher members exists as liquids or solids.

2. For a particular alkyl group R, what is the correct order of boiling points of the following compounds?
a) RBr > RCl > RF
b) RF > RCl > RBr
c) RCl > RBr > RF
d) RF > RBr > RCl

Explanation: As the size of halogen atom increases, the magnitude of van der Waal forces increases, that is why RF has the lowest boiling point as it is the smallest halogen atom with weakest van der Waal attraction.

3. What is the correct relation between boiling points of the following alkyl iodides, where R=methyl, R’=ethyl and R”=propyl?
a) RI > R’I > R”I
b) R”I > R’I > RI
c) RI = R’I = R”I
d) R”I = R’I > RI

Explanation: The forces of attraction become stronger as the molecules getter bigger in size and number of electrons increases. Hence, the methyl halides will have the lowest boiling points among all alkyl groups.
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4. If chloromethane has a boiling point of 250K, what will be the probable boiling point of methane?
a) 110K
b) 250K
c) 275K
d) 315K

Explanation: Haloalkanes are polar in nature and have higher intermolecular forces of attraction in terms of dipole-dipole and van der Waal forces. Hence, the boiling points of haloalkanes are higher than their respective hydrocarbons.

5. Which of the following has the highest boiling point?
a) Chloromethane
b) Dichloromethane
c) Trichloromethane
d) Tetrachloromethane

Explanation: The boiling points increase with the number of halogen atoms as the molecular masses increase and so do the intermolecular forces of attraction.

6. The boiling points of isomeric alkyl halides _______ with increase in branching.
a) increase
b) decrease
c) remains same
d) cannot be determined

Explanation: The branching of compounds makes it more compact and reduces the surface area, which in turn van der Waals attraction forces and thus, decrease the boiling point.

7. If the compound shown has a boiling point of 346K, predict the boiling point of n-Butyl bromide?

a) 300K
b) 325K
c) 350K
d) 375K

Explanation: The compound shown is a highly branched isomer of n-Butyl bromide, i.e., tert-Butyl bromide. The n-Butyl bromide structure has no branches and therefore has a significantly higher boiling point than tert-Butyl bromide.

8. What is the correct order of boiling of isomeric dichlorobenzenes?
a) ortho>meta>para
b) para>meta>ortho
c) para>ortho>meta
d) meta>ortho>para

Explanation: Para isomers have the highest melting points due to their symmetry and ease with which they can fit into a crystal lattice compared to meta and ortho isomers.

9. The dipole moment of chloromethane is higher than that of fluoromethane.
a) True
b) False

Explanation: Although the F atom is much more electronegative than Cl, the very small size of F compared to Cl results in the product of charge and distance, i.e., dipole moment, of CH3F to be lower than that of CH3Cl.

10. What is the value of diploe moment of p-Dichlorobenzene?
a) 0
b) 1
c) >1
d) <1

Explanation: The para isomer of dichlorobenzene is symmetrical and the two equal dipoles on opposite sides cancel and result in zero dipole moment.

11. Calculate the dipole moment of m-Dichlorobenzene if the dipole moments of C-Cl bonds are 1.72D.
a) 0
b) 1.72D
c) 2.54D
d) 2.98D

Explanation: The angle between the two halogen atoms in meta isomer is 120° and let the dipole moments of C-Cl bonds be d=1.72D and let d’ be the dipole moment of the compound. So, by law of parallelogram of forces,
$$\Rightarrow \,d’ = \sqrt{d^2 + d^2 + 2d^2.cos(120°)}$$
$$\Rightarrow \,d’ = \sqrt{1.72^2 + 1.72^2 – (2 \,x\, 0.5 \,x\, 1.72^2)}$$
$$\Rightarrow \,d’ = \sqrt{1.72^2}$$
$$\Rightarrow \,d’ = 1.72D$$

12. Which of the following has the highest density?
a) CH3Cl
b) CH2Cl2
c) CHCl3
d) CCl4

Explanation: The density of haloalkanes increases with the number of halogen atoms present in because of increase in molecular weight.

13. Haloalkanes are more soluble in water than in alcohols.
a) True
b) False

Explanation: Haloalkanes are very slightly soluble in water due to the strong hydrogen bonds between water molecules. However, they dissolve much more easily in organic solvents as the strength of new forces is similar to that of existing intermolecular attractions.

14. Which of the following has the lowest boiling point?
a) Bromomethane
b) Bromoform
c) Chloromethane
d) Dibromomethane

Explanation: Since boiling point increases with increases in molecular mass, chloromethane has the lowest molecular mass and hence the lowest boiling point.

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