Physical Properties - UNSOLVED PRACTICE SET
Chapter: Haloalkanes and Haloarenes | Topic: Physical Properties
PHYSICAL PROPERTIES - UNSOLVED PRACTICE SET
Topic: Physical Properties
Multiple Choice Questions
Q1. The boiling points of haloalkanes are higher than corresponding alkanes because:
- They have higher molecular mass
- They have dipole-dipole interactions
- They have stronger van der Waals forces
- All of the above
Q2. The boiling points of alkyl halides decrease in the order:
- RI > RBr > RCl > RF
- RF > RCl > RBr > RI
- RCl > RBr > RI > RF
- RBr > RI > RCl > RF
Q3. Among isomeric alkyl halides, the boiling point is highest for:
- Primary alkyl halide
- Secondary alkyl halide
- Tertiary alkyl halide
- All have the same boiling point
Q4. Haloalkanes are generally:
- Soluble in water
- Insoluble in water but soluble in organic solvents
- Soluble in both water and organic solvents
- Insoluble in both water and organic solvents
Q5. The density of alkyl halides is:
- Less than water
- Greater than water
- Equal to water
- Variable
Q6. The boiling point of p-dichlorobenzene is higher than o-dichlorobenzene because:
- It has a higher dipole moment
- It has a more symmetrical structure with better packing
- It has stronger hydrogen bonding
- It has a lower molecular mass
Short Answer Questions
Q7. Explain why the boiling point of bromoethane is higher than that of chloroethane, which in turn is higher than fluoroethane.
Q8. Why are alkyl halides insoluble in water? Explain in terms of intermolecular forces.
Q9. The boiling point of n-butyl bromide is higher than isobutyl bromide. Explain why.
Q10. Why do aryl halides have higher boiling points than alkyl halides of comparable molecular mass?
Q11. Explain why CCl₄ is used as a solvent in organic chemistry despite being toxic.
Q12. The density of chloroform is 1.49 g/mL. Why does chloroform form a separate layer below water when mixed?
Long Answer Questions
Q13. (a) Discuss the trends in boiling points of haloalkanes. Explain the factors affecting boiling points.
(b) Arrange the following in order of increasing boiling points:
CH₃Cl, CH₃Br, CH₃I, CH₃F
Give reasons for your arrangement.
(c) Why do tertiary alkyl halides have lower boiling points than primary alkyl halides with the same number of carbon atoms?
Q14. (a) Discuss the solubility of haloalkanes and haloarenes in water and organic solvents.
(b) Why are alkyl halides generally insoluble in water despite being polar?
(c) Explain why the solubility of alkyl halides in water decreases as the size of the alkyl group increases.
(d) Why is CCl₄ an excellent solvent for non-polar organic compounds but not for ionic compounds?
Q15. (a) Discuss the trends in density of haloalkanes.
(b) Why is the density of alkyl halides greater than that of corresponding alkanes?
(c) Arrange the following in order of increasing density:
CH₃Cl, CH₂Cl₂, CHCl₃, CCl₄
Explain the trend.
(d) Why is the density of bromoform (CHBr₃) very high (2.89 g/mL)?
Numerical / Application-Based Problems
Q16. The following table gives boiling point data for some alkyl halides:
| Compound | Molecular Mass (g/mol) | Boiling Point (°C) |
|---|---|---|
| CH₃Cl | 50.5 | -24.2 |
| CH₃Br | 94.9 | 3.6 |
| CH₃I | 141.9 | 42.4 |
| C₂H₅Cl | 64.5 | 12.3 |
| C₂H₅Br | 109.0 | 38.4 |
| C₂H₅I | 156.0 | 72.3 |
| C₃H₇Cl | 78.5 | 46.6 |
| C₃H₇Br | 123.0 | 71.0 |
| C₃H₇I | 170.0 | 102.5 |
(a) Plot a graph of boiling point vs. molecular mass for CH₃X (X = Cl, Br, I).
(b) What trend do you observe? Explain the trend in terms of intermolecular forces.
(c) Compare the boiling points of C₂H₅Cl and C₃H₇Cl. By how much does the boiling point increase per CH₂ group?
(d) For the same alkyl group, calculate the average increase in boiling point when Cl is replaced by Br, and when Br is replaced by I.
(e) Predict the boiling point of C₄H₉Br based on the trend observed.
Q17. The following data gives density and solubility information:
| Compound | Density (g/mL) | Solubility in Water (g/100 mL) |
|---|---|---|
| CH₃Cl | 0.92 | 0.74 |
| CH₂Cl₂ | 1.33 | 1.3 |
| CHCl₃ | 1.49 | 0.8 |
| CCl₄ | 1.59 | 0.08 |
| C₆H₅Cl | 1.11 | 0.05 |
| C₆H₅Br | 1.49 | Insoluble |
(a) Plot a graph of density vs. number of chlorine atoms for CH₃Cl, CH₂Cl₂, CHCl₃, and CCl₄.
(b) Explain why density increases with increasing halogen substitution.
(c) Explain why solubility in water decreases as the number of chlorine atoms increases, despite increasing polarity.
(d) Why is C₆H₅Cl less soluble than CH₃Cl even though it has a higher molecular mass and similar polarity?
(e) A chemist needs a solvent that is denser than water and immiscible with water for extraction purposes. Which compound from the table would be most suitable? Why?
Q18. In a school science project, students investigate the physical properties of common haloalkanes found at home.
(a) A student finds a bottle of iodine tincture in the medicine cabinet. The label says it contains iodine dissolved in ethanol. Why isn't water used as the solvent? (Consider the solubility of I₂ in different solvents.)
(b) Another student finds that his father's shaving cream contains trichlorofluoromethane (CCl₃F) as a propellant. Why was this compound used as a propellant? (Consider its boiling point and vapour pressure.)
(c) A third student learns that chloroform was historically used as an anaesthetic. Why is it no longer used for this purpose? What physical property made it suitable as an anaesthetic?
(d) The students measure the density of a sample of bromoform (CHBr₃) and find it to be 2.89 g/mL. Why is this density so high? Would bromoform float or sink in water?
(e) The teacher asks: "If you were designing a fire extinguisher for electrical fires, which property of CCl₄ would make it suitable? Why has it been replaced by other compounds?" Give your answer.