On complete combustion 1.0 g of an organic compound (X) gave 1.46 g of CO₂ and 0.567 g of H₂ O. The empirical formula mass of compound (X) is __________ g. (Given molar mass in g mol⁻¹ C: 12, H: 1, O: 16 )

Solution

Chemistry ma’am · 3 steps

Get C from CO₂ and H from H₂O, then whatever mass is left over is oxygen.

1. Carbon and hydrogen. All the carbon ends up in CO₂, so its mass is 1.46 × 12/44 = 0.398 g. All the hydrogen ends up in H₂O, so its mass is 0.567 × 2/18 = 0.063 g.
2. Oxygen by difference. Oxygen cannot be measured from the products because the O₂ used for burning also supplies oxygen. So take it as the leftover mass: 1.0 - 0.398 - 0.063 = 0.539 g.

   Element	Mass (g)	Moles	Divide by smallest
   C	0.398	0.398/12 = 0.0332	1
   H	0.063	0.063/1 = 0.063	1.90 ≈ 2
   O	0.539	0.539/16 = 0.0337	1.01 ≈ 1

3. So. The empirical formula is CH₂O, and its mass is 12 + 2 + 16 = 30 g, which is option (c).

The idea to keep. In combustion analysis, C comes from CO₂ (12/44), H comes from H₂O (2/18), and O is always found by subtracting from the sample mass.

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