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Aldehydes and Ketones - ISC Class 12 Chemistry Questions with Answers, Page 2

56 past-paper questions on Aldehydes and Ketones from ISC Class 12 Chemistry papers (2027-2018), newest first, in full. Questions 21-40 are on this page, 20 to a page. Tap "Show answer" under a question to see its answer.

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2025 · 5 marks · Case basedOpen: The aldol condensation takes its name from aldol (3-hydroxybutanal) a name…
The aldol condensation takes its name from aldol (3-hydroxybutanal) a name introduced by Wurtz who first prepared the beta-hydroxy aldehyde from acetaldehyde in 1872. It is a base catalysed reaction, and the product of aldol condensation undergoes dehydration of intermediate beta-aldols or beta-ketals in presence of a dilute acid to form $\alpha, \beta$ unsaturated carbonyl compound. Source: https://www.researchgate.net/publication/229950129_The_Aldol_Condensation
(a)[2.0]
Write the mechanism of aldol condensation starting with acetaldehyde.
(b)[1.0]
Name the base used highlighting the role of the base catalyst in facilitating the reaction.
(c)[2.0]
What is crossed aldol condensation? Name the product formed when benzaldehyde undergoes crossed aldol condensation with acetaldehyde.

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2025 · 2 marks · Short answerOpen: Identify the compounds [A] and [B] in the following reactions:
Identify the compounds [A] and [B] in the following reactions:
(a)[1.0]
$\text{C}_6\text{H}_5\text{CHO} \xrightarrow[\text{(2) }\text{SOCl}_2]{\text{(1) }\text{K}_2\text{Cr}_2\text{O}_7/\text{H}_2\text{SO}_4} [\text{A}] \xrightarrow{\text{C}_6\text{H}_6(\text{anhy. }\text{AlCl}_3)} [\text{B}]$
(b)[1.0]
$\text{CH}_3\text{-C}\equiv\text{CH} \xrightarrow[\text{(2) vigorous oxidation, conc. }\text{HNO}_3]{\text{(1) }\text{H}_2\text{SO}_4/\text{HgSO}_4} [\text{A}] \xrightarrow{\text{C}_2\text{H}_5\text{OH } [\text{conc. }\text{H}_2\text{SO}_4]} [\text{B}]$

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2025 · 2 marks · Short answerOpen: Three organic compounds A, B and C are non cyclic functional isomers of…
Three organic compounds A, B and C are non cyclic functional isomers of carbonyl compounds with molecular formula $\text{C}_4\text{H}_8\text{O}$. Isomers A and C give positive Tollen’s test while compound B does not give positive Tollen’s test but gives positive iodoform test. Compounds A and B on reduction with Zn amalgam and conc. $\text{HCl}$ give the same product.
(a)[1.0]
Write the structures of the compounds A, B and C.
(b)[1.0]
Out of the compounds A, B and C, which one will be the least reactive towards addition of $\text{HCN}$.

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2025 · 2 marks · Short answerOpen: Identify the compounds [A] and [B] in the following reactions:
Identify the compounds [A] and [B] in the following reactions:
(a)[1.0]
$\text{CH}_3\text{CHO} \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7 + \text{H}_2\text{SO}_4]{[\text{O}]} \text{CH}_3\text{COOH} \xrightarrow{\text{Ca(OH)}_2} [\text{A}] \xrightarrow[\text{dry distillation}]{\Delta} [\text{B}]$
(b)[1.0]
$\text{CH}_3\text{COCH}_3 \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7 + \text{H}_2\text{SO}_4]{[\text{O}]} [\text{A}] \xrightarrow{\text{PCl}_5} \text{CH}_3\text{COCl} \xrightarrow[\text{Pd/BaSO}_4 \text{, Boiling xylene}]{\text{H}_2} [\text{B}]$

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2025 · 5 marks · Case basedOpen: ‘In 1915, a senior lecturer in Biochemistry at the University of Manchester…
‘In 1915, a senior lecturer in Biochemistry at the University of Manchester named Dr. Chaim Weizmann invented a fermented process that converts starch into acetone and butanol by using Clostridium acetobutylicum. Acetone was the key component in the production of the smokeless gunpowder (cordite) used by the Allies in World War I. Acetone was previously made from calcium acetate imported from Germany, since Allies were in war with Germany, this was no longer possible.’ Source: https://www.weizmann.ac.il/WeizmannCompass/sections/people-behind-the-science/chaim-weizmann%E2%80%99s-acetone-patent-turns-100
(a)[2.0]
How will you prepare acetone from calcium acetate?
(b)[2.0]
If butan-2-ol is oxidised by $\text{K}_2\text{Cr}_2\text{O}_7$, which ketone will be produced? Give the balanced chemical reaction.
(c)[1.0]
How would you obtain acetone from acetyl chloride?

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2025 · 2 marks · Short answerOpen: An organic compound [A] which has characteristic odour, reacts with conc. to…
An organic compound [A] which has characteristic odour, reacts with conc. $\text{NaOH}$ to give two compounds [B] and [C]. Compound [B] has molecular formula $\text{C}_7\text{H}_8\text{O}$ which upon oxidation gives back compound [A]. Compound [C] is the sodium salt of the acid and upon treatment with sodalime yields an aromatic hydrocarbon [D]. Identify the compounds [A], [B], [C] and [D].

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2024 · 5 marks · Short answerOpen: An organic compound [A], having a specific smell forms two compounds [B] and…
(i)[3.0]
An organic compound [A], having a specific smell forms two compounds [B] and [C] by reacting with conc. sodium hydroxide. The molecular formula of compound [B] is $\text{C}_7\text{H}_8\text{O}$, which forms compound [A] again on oxidation. Compound [C] forms benzene on heating with soda lime. Write the structures of compounds [A], [B] and [C]. Also, write the reactions involved.
(ii)[2.0]
Identify the compounds [A] and [B] in the reactions given below: (a) $\text{C}_6\text{H}_6 \xrightarrow[\text{AlCl}_3(\text{anhy.})]{\text{CH}_3\text{Cl}} [\text{A}] \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7 + \text{H}_2\text{SO}_4]{[\text{O}]} [\text{B}]$ (b) $\text{CH}_3\text{-CHOH-CH}_3 \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7 + \text{H}_2\text{SO}_4]{[\text{O}]} [\text{A}] \xrightarrow{\text{NH}_2\text{OH}} [\text{B}]$

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2024 · 5 marks · Short answerOpen: Give a reason for each of the following: (a) Formaldehyde does not undergo…
(i)[3.0]
Give a reason for each of the following: (a) Formaldehyde does not undergo aldol condensation, but acetaldehyde does. (b) Chloroacetic acid is stronger acid than acetic acid. (c) Both aldehydes and ketones undergo a number of nucleophilic addition reactions.
(ii)[2.0]
An organic compound with the molecular formula $\text{C}_7\text{H}_6\text{O}$ gets oxidised by Tollens' reagent. It does not respond to Fehling test but can undergo the Cannizzaro reaction. Identify the compound. Show how you used the above information to identify the compound.

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2024 · 2 marks · Short answerOpen: An organic compound [A] having molecular formula forms a compound [B] with…
An organic compound [A] having molecular formula $\text{C}_4\text{H}_{10}\text{O}$ forms a compound [B] with molecular formula $\text{C}_4\text{H}_8\text{O}$ on oxidation. Compound [B] gives a positive iodoform test. The reaction of compound [B] with $\text{CH}_3\text{MgBr}$ followed by hydrolysis gives compound [C] with molecular formula $\text{C}_5\text{H}_{12}\text{O}$. Identify the compounds [A], [B] and [C]. Write the reaction for the conversion of compound [A] to compound [B].

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2024 · 3 marks · Short answerOpen: An organic compound gives red precipitate when heated with Fehling solution. It…
An organic compound $\text{C}_2\text{H}_4\text{O}$ gives red precipitate when heated with Fehling solution. It also undergoes aldol condensation in the presence of dilute $\text{NaOH}$.
(i)[1.0]
Identify the organic compound and write its IUPAC name.
(ii)[1.0]
Which compound will be formed when this organic compound reacts with hydroxylamine?
(iii)[1.0]
What is observed when the compound, referred to in subpart (i), is heated with ammonical silver nitrate?

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2024 · 3 marks · Short answerOpen: Identify the compounds [A], [B] and [C].
Identify the compounds [A], [B] and [C].
(i)[1.5]
$\text{C}_6\text{H}_5\text{COOH} \xrightarrow{\text{PCl}_5} [\text{A}] \xrightarrow{+\text{H}_2\text{, } \text{Pd/BaSO}_4} [\text{B}] \xrightarrow{\text{KCN (alc), distil}} [\text{C}]$
(ii)[1.5]
$\text{H}-\text{C}\equiv\text{C}-\text{H} + \text{H}_2\text{O} \xrightarrow{\text{Hg}^{2+}/\text{H}_2\text{SO}_4} [\text{A}] \xrightarrow[\text{K}_2\text{Cr}_2\text{O}_7/\text{H}_2\text{SO}_4]{\text{[Oxidation]}} [\text{B}] \xrightarrow[(ii)\text{ dry distillation}]{\text{(i) } \text{Ca(OH)}_2} [\text{C}]$

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