Physical Properties - UNSOLVED PRACTICE SET
Chapter: Aldehydes Ketones and Carboxylic Acids | Topic: Physical Properties
PHYSICAL PROPERTIES - UNSOLVED PRACTICE SET
Topic: Physical Properties
Multiple Choice Questions
Q1. The boiling points of aldehydes and ketones are higher than corresponding alkanes because of:
- Higher molecular mass
- Dipole-dipole interactions
- Hydrogen bonding
- Both (a) and (b)
Q2. The solubility of aldehydes and ketones in water is due to:
- Hydrogen bonding with water
- Dipole-dipole interactions
- Both (a) and (b)
- Covalent bonding with water
Q3. Which of the following has the highest boiling point?
- CH₃CHO
- CH₃COCH₃
- CH₃CH₂CHO
- CH₃CH₂CH₂CHO
Q4. The smell of bitter almonds is characteristic of:
- Acetone
- Benzaldehyde
- Formaldehyde
- Acetaldehyde
Q5. Lower aldehydes are soluble in water because:
- They form hydrogen bonds with water
- They have low molecular mass
- They are polar
- All of the above
Q6. The density of aldehydes and ketones is generally:
- Less than water
- Greater than water
- Equal to water
- Variable
Short Answer Questions
Q7. Why do aldehydes and ketones have higher boiling points than ethers of comparable molecular mass?
Q8. Explain why formaldehyde and acetaldehyde are miscible with water in all proportions, while higher aldehydes are only partially soluble.
Q9. Arrange the following in order of increasing boiling points: CH₃CHO, CH₃CH₂CHO, CH₃COCH₃, CH₃CH₂CH₂CHO. Give reasons.
Q10. Why do aldehydes and ketones have lower boiling points than alcohols of comparable molecular mass?
Q11. What is the smell of acetone? Why is it used as a nail polish remover?
Q12. Your mother uses vanilla essence in baking. What compound gives vanilla its characteristic smell? Write its structure.
Long Answer Questions
Q13. (a) Discuss the physical properties of aldehydes and ketones with respect to:
(i) Boiling points
(ii) Solubility in water
(iii) Density
(iv) Smell
Explain each property in terms of intermolecular forces.
Q14. (a) Compare the boiling points of:
(i) Aldehydes vs. alkanes
(ii) Aldehydes vs. alcohols
(iii) Aldehydes vs. ethers
Give reasons for the differences.
(b) Explain why the solubility of aldehydes and ketones in water decreases as the size of the alkyl group increases.
Q15. (a) Discuss the physical state of aldehydes and ketones at room temperature.
(b) Why are lower aldehydes (formaldehyde, acetaldehyde) gases or volatile liquids, while higher aldehydes are liquids or solids?
(c) Explain why aromatic aldehydes and ketones are generally liquids or solids at room temperature.
Numerical / Application-Based Problems
Q16. The following table gives boiling point data for some compounds:
| Compound | Molecular Mass (g/mol) | Boiling Point (°C) |
|---|---|---|
| CH₃CHO | 44 | 20 |
| CH₃CH₂CH₃ | 44 | -42 |
| CH₃OCH₃ | 46 | -24 |
| CH₃CH₂OH | 46 | 78 |
| CH₃COCH₃ | 58 | 56 |
| CH₃CH₂CH₂CH₃ | 58 | -0.5 |
| CH₃CH₂OCH₃ | 60 | 8 |
| CH₃CH₂CH₂OH | 60 | 97 |
(a) Compare the boiling points of CH₃CHO and CH₃CH₂CH₃ despite similar molecular masses. Explain the difference.
(b) Compare the boiling points of CH₃COCH₃ and CH₃CH₂OCH₃ despite similar molecular masses. Explain.
(c) Plot a graph of boiling point vs. molecular mass for aldehydes/ketones and their corresponding alkanes.
(d) Calculate the difference in boiling points between each carbonyl compound and its corresponding alkane. What trend do you observe?
(e) A student claims that hydrogen bonding is the main reason for the higher boiling points of aldehydes compared to alkanes. Is this correct? Explain.
Q17. The following data relates to the solubility of aldehydes and ketones in water:
| Compound | Solubility (g/100 mL water at 20°C) |
|---|---|
| HCHO | Miscible |
| CH₃CHO | Miscible |
| CH₃COCH₃ | Miscible |
| CH₃CH₂CHO | 7.1 |
| CH₃CH₂COCH₃ | 5.5 |
| C₆H₅CHO | 0.3 |
| C₆H₅COCH₃ | Insoluble |
(a) Explain why solubility decreases as the carbon chain length increases.
(b) Why is acetone used as a universal solvent in laboratories? (Consider its solubility in both water and organic solvents.)
(c) Calculate the number of carbon atoms at which the aldehyde becomes practically insoluble in water.
(d) Why is benzaldehyde much less soluble than butanal despite having a similar number of carbon atoms?
(e) A paint manufacturer wants to use a solvent that dissolves both water-based and oil-based pigments. Which compound from the table would be most suitable? Why?
Q18. In a school science project, students investigate the physical properties of aldehydes and ketones in everyday life.
(a) A student finds that her nail polish remover contains acetone. Why is acetone used for this purpose? (Consider volatility and solvent properties.)
(b) Another student learns that formaldehyde is used to preserve biological specimens. Why is it effective as a preservative? (Consider its reactivity with proteins.)
(c) A third student discovers that benzaldehyde is used in food flavouring (almond flavour). Why does it have this characteristic smell? (Consider its molecular structure.)
(d) The students measure the density of different aldehydes and ketones. Arrange the following in order of increasing density: CH₃CHO, CH₃COCH₃, C₆H₅CHO, C₆H₅COCH₃. Explain.
(e) The teacher asks: "If you were designing a new perfume, would you choose an aldehyde or a ketone as the base note? Why?" Give your answer with reasoning.