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Chemistry · 2026 · 5 marks
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic Acids5 marksApplylong answer
CBSE 2026 · Region 3 · Set 2 · Q33
(a) (i) Write the product(s) when: (I) One mol of ethanal is treated with 1 mol of CH_3 OH in the presence of dry HCl gas. (II) Benzaldehyde is…
(i)
Write the product(s) when :
(I)
One mol of ethanal is treated with $\displaystyle 1$ mol of $\displaystyle \mathrm{CH}_{3} \mathrm{OH}$ in the presence of dry HCl gas.
(II)
Benzaldehyde is treated with conc. NaOH .
(III)
Ethanoic acid is heated in the presence of $\displaystyle \mathrm{P}_{2} \mathrm{O}_{5}$.
(ii)
Write a simple chemical test to distinguish between Ethanal and Propanal.
(iii)
Write the name of the reagent to transform Allyl alcohol to Propenal.
(i)
Draw the structure of the semicarbazone of acetone.
(ii)
Why are $\displaystyle \alpha$-hydrogen atoms of aldehydes and ketones acidic in nature ?
(iii)
Arrange the following compounds in increasing order of their reactivity towards HCN : $\displaystyle \mathrm{CH}_{3} \mathrm{COCH}_{3}, \mathrm{CH}_{3} \mathrm{CHO}$,
(iv)
Write the reaction involved in Etard reaction.
(v)
Write the product when reacts with Zn(Hg)/conc. HCl.
Marking-scheme solution
(i)
(I)
(II)
(III)
(CH3CO)2O
(ii)
On heating with NaOH + I2, ethanal gives yellow ppt. of CHI3
whereas propanal does not.
(iii)
PCC
(i)
(ii)
Because of electron withdrawing nature of carbonyl group / Because
of resonance stabilisation of its conjugate base.
(iii)
(iv)
(v)
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.