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Get your chemical equations right

Class 12 chemistry is not too tough to crack if you master tricky questions like these.

education Updated: Jan 29, 2015 10:58 IST

Class 12 chemistry is not too tough to crack if you master tricky questions like these.

Q1.An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollen’s reagent but forms an addition compound with sodium hydrogen sulphite and gives a positive iodoform test. On vigorous oxidation, it gives ethanoic acid and propanoic acid. Write the possible structure of the compound.

Solution
C = 69.77%, H = 11.67%
∴ O = 100 – (69.77 + 11.63)%
= 18.6 %
∴ C : H : O = 69.77/12 : 11.63/1 : 18.6/16 = 5.88 : 11.63 : 1.16 : : 5 : 10 : 1
The empirical formula of the given compound = C5H10O
Empirical formula mass = 5 × 12 + 10 × 1 + 1 × 16 = 86
Molar mass = 86 (given)
∴ Molecular formula = C5H10O

Since the compound form sodium hydrogen sulphite is an addition product, therefore, it must be either an aldehyde or methyl ketone. Since the compound does not reduce Tollen’s reagent therefore, it cannot be an aldehyde and hence it must be a methyl ketone. Since the compound gives positive iodoform test, therefore, the given compound is a methyl ketone. Since the given compound on vigorous oxidation gives a mixture of ethanoic acid and propanoic acid, therefore, the methyl ketone is pentan 2-one, i.e.,


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