A chloro compound "A".
(i) forms aldehydes on ozonolysis followed by the hydrolysis.
(ii) when vaporized completely 1.53 g of A, gives 448 mL of vapour at STP.
The number of carbon atoms in a molecule of compound A is ___________.

Solution

Chemistry ma’am · 4 steps

Vapour volume gives moles, mass over moles gives molar mass, and an alkyl chloride formula finishes it.

1. Moles of vapour. At STP one mole of any gas occupies 22.4 L. So 448 mL is 0.448/22.4 = 0.02 mol of A.
2. Molar mass. M = (1.53 g)/(0.02 mol) = 76.5 g mol⁻¹.
3. Choose the formula. Ozonolysis needs a C=C bond, so A is a monochloro alkene, CₙH₂ₙ₋₁Cl. Its molar mass is 12n + (2n-1) + 35.5 = 14n + 34.5.

   14n + 34.5 = 76.5 ⇒ n = 3

4. So. A is C₃H₅Cl, for example CH₂=CH-CH₂Cl. On ozonolysis it gives HCHO and ClCH₂CHO, which are both aldehydes. The number of carbon atoms is 3.

The idea to keep. Gas volume at STP gives you moles, and mass divided by moles gives molar mass. Then use the chemical clue, here ozonolysis meaning a C=C bond, to pick the general formula and solve for n.

Answer from the NTA final answer key. Solution by PrepWiser.