Chemistry Questions and Answers – Aldehydes and Ketones Physical Properties

«
»

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

1. Which of the following exists as a gas at 287K?
a) Formaldehyde
b) Acetaldehyde
c) Propanal
d) Acetone
View Answer

Answer: a
Explanation: Methanal exists as foul-smelling gas at room temperature. Ethanal is a volatile liquid which boils at 294K. Other aldehydes and ketones exist as either liquids or solids at room temperature.
advertisement

2. If the boiling points of methoxyethane and propanol are 281 K and 370 K respectively, predict the boiling point of propanal.
a) 273 K
b) 281 K
c) 322 K
d) 370 K
View Answer

Answer: c
Explanation: The boiling point of aldehydes are higher than those of non-polar hydrocarbons of comparable molecular masses. However, their boiling points are lower than comparable alcohols, due to the absence of intermolecular hydrogen bonding.

3. Which of the following is the least soluble in water?
a) Methanal
b) Ethanal
c) Propanone
d) Pentanal
View Answer

Answer: d
Explanation: The lower aldehydes and ketones are miscible in water in all proportions due to the ability of the polar carbonyl group to form hydrogen bonds with water molecules. However, the solubility rapidly decreases as the length of the alkyl chain increases. Precisely, aldehydes and ketones with more than 4 carbon atoms are practically insoluble in water.
advertisement
advertisement

4. Propanal has a slightly higher boiling point than propanone.
a) True
b) False
View Answer

Answer: b
Explanation: Propanone has two CH3 groups, one on either side of the CO group, whereas propanal has only one CH3CH2 group. This makes propanone more polar because of the higher electron releasing effect of two alkyl groups. The boiling point of propanal is 322K and that of propanone is 329K.

5. Two compounds A and B were being tested for their boiling points. It was observed that A started boiling after B, when both were subjected to same conditions. If the compound B is acetone, which of the following can be compound A?
a) n-Butane
b) Methoxyethane
c) Propanal
d) Propanol
View Answer

Answer: d
Explanation: It can be inferred that B has a higher boiling point than A. Since hydrocarbons, ethers and aldehydes have lower boiling points than ketones of similar molecular masses, none of them can be compound A. Also, alcohols have a higher boiling point than similar ketones hence, the compound A is propanol.
advertisement

6. Which of the following has the least pungent odour?
a) Methanal
b) Ethanal
c) Propanal
d) Butanal
View Answer

Answer: d
Explanation: As the size of the aldehyde molecule increases, the odour becomes less pungent and more fragrant. Methanal is the most pungent smelling aldehyde.

7. Which of the following is used as a flavouring agent?
a) Methanal
b) Ethanal
c) Acetone
d) Acetophenone
View Answer

Answer: d
Explanation: Methanal, ethanal and acetone are lower carbonyl compounds and are not much fragrant to be used as flavouring agents.
advertisement

Sanfoundry Global Education & Learning Series – Chemistry – Class 12.

To practice all areas of Chemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.

advertisement

advertisement
advertisement
Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

Youtube | Telegram | LinkedIn | Instagram | Facebook | Twitter | Pinterest
Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

Subscribe to his free Masterclasses at Youtube & technical discussions at Telegram SanfoundryClasses.