Class 12 Aldehydes, Ketones and Carboxylic Acids Mock Test (CBSE)

Topics in Aldehydes, Ketones and Carboxylic Acids

• Nomenclature and structure of carbonyl group
• Preparation of aldehydes and ketones
• Physical properties of aldehydes and ketones
• Nucleophilic addition reactions
• Oxidation and reduction of carbonyl compounds
• Aldol and Cannizzaro reactions
• Uses of aldehydes and ketones
• Nomenclature and structure of carboxyl group
• Methods of preparation of carboxylic acids
• Acidity of carboxylic acids
• Chemical reactions of carboxylic acids

Aldehydes, Ketones and Carboxylic Acids practice questions with answers

1. Q1Multiple choice·1 mark
   During an experimental laboratory investigation to prepare specific carbonyl compounds, a researcher oxidizes a primary alcohol using PCC (pyridinium chlorochromate) in dichloromethane. What is the primary experimental observation and product outcome of this specific method compared to using acidified $KMnO_4$?

   1. (a)Immediately yields a carboxylic acid with vigorous effervescence of carbon dioxide
   2. (b)Produces a symmetrical ketone via carbon-carbon bond cleavage
   3. (c)Stops selectively at the aldehyde stage without over-oxidizing to the carboxylic acid
   4. (d)Forms an unreactive ester intermediate that precipitates out of the solution
   Show answer and step marks

   1. Correct option: (c) Stops selectively at the aldehyde stage without over-oxidizing to the carboxylic acid+1

   Answer: (c)
2. Q2Assertion and reason·1 mark
   Assertion (A): Presence of electron-withdrawing groups like $-\text{NO}_2$ on the benzene ring of benzoic acid increases its acidity. Reason (R): Electron-withdrawing groups stabilize the carboxylate anion through electron-withdrawing inductive and resonance effects, facilitating proton release.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).+1

   Answer: (a)
3. Q3Multiple choice·1 mark
   Low boiling points of aldehydes and ketones compared to corresponding alcohols of comparable molecular masses are primarily explained by which of the following molecular interactions?

   1. (a)Absence of intermolecular hydrogen bonding in aldehydes and ketones, as their molecules are only associated through weaker dipole-dipole interactions
   2. (b)Steric hindrance from alkyl groups preventing any form of intermolecular attraction in liquid phases
   3. (c)Significantly lower molecular weight profiles resulting from high volatility carbonyl group polarization
   4. (d)Formation of unstable cyclic dimers that evaporate rapidly at room temperature
   Show answer and step marks

   1. Correct option: (a) Absence of intermolecular hydrogen bonding in aldehydes and ketones, as their molecules are only associated through weaker dipole-dipole interactions+1

   Answer: (a)
4. Q4Assertion and reason·1 mark
   Assertion (A): Aldehydes that do not have an $\alpha$-hydrogen atom undergo Cannizzaro reaction when treated with concentrated alkali. Reason (R): This reaction is a disproportionation reaction where one molecule of aldehyde is oxidized to carboxylic acid salt and another is reduced to alcohol.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).+1

   Answer: (a)
5. Q5Short answer·2 marks
   Write the chemical equation for the reaction of benzaldehyde with concentrated sodium hydroxide solution. Name the reaction and state its general characteristic feature.
   Show answer and step marks

   1. Chemical equation: $2\text{C}_6\text{H}_5\text{CHO} + \text{NaOH (conc.)} \rightarrow \text{C}_6\text{H}_5\text{CH}_2\text{OH} + \text{C}_6\text{H}_5\text{COONa}$+1
   2. Name: Cannizzaro reaction.+0.5
   3. Characteristic feature: it is a disproportionation (self-oxidation-reduction), one aldehyde molecule being reduced to the alcohol and another oxidised to the carboxylate salt; it is shown by aldehydes with no $\alpha$-hydrogen (either point earns the mark).+0.5

   Answer: $2\text{C}_6\text{H}_5\text{CHO} + \text{NaOH} \rightarrow \text{C}_6\text{H}_5\text{CH}_2\text{OH} + \text{C}_6\text{H}_5\text{COONa}$; Cannizzaro reaction, a disproportionation (one molecule reduced, one oxidised) shown by aldehydes without $\alpha$-hydrogen.
6. Q6Short answer·2 marks
   What happens when benzaldehyde is treated with concentrated sodium hydroxide solution? Write the chemical equation for the reaction involved.
   Show answer and step marks

   1. Identify the reaction as the Cannizzaro reaction: benzaldehyde (no $\alpha$-hydrogen) disproportionates into benzyl alcohol and sodium benzoate.+1
   2. Write the balanced chemical equation: $2\text{C}_6\text{H}_5\text{CHO} + \text{NaOH (conc.)} \rightarrow \text{C}_6\text{H}_5\text{CH}_2\text{OH} + \text{C}_6\text{H}_5\text{COONa}$.+1

   Answer: Cannizzaro reaction giving benzyl alcohol and sodium benzoate: $2\text{C}_6\text{H}_5\text{CHO} + \text{NaOH} \rightarrow \text{C}_6\text{H}_5\text{CH}_2\text{OH} + \text{C}_6\text{H}_5\text{COONa}$

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