120 g of an organic compound that contains only carbon and hydrogen gives 330 g of CO₂ and 270 g of water on complete combustion. The percentage of carbon and hydrogen, respectively are

Solution

Chemistry ma’am · 4 steps

Every carbon atom ends up in CO₂ and every hydrogen in H₂O, so trace each element back.

1. Carbon from CO2. 44 g of CO₂ contains 12 g of carbon. So 330 g of CO₂ contains 330 × 12/44 = 90 g of carbon.
2. Hydrogen from water. 18 g of H₂O contains 2 g of hydrogen. So 270 g of H₂O contains 270 × 2/18 = 30 g of hydrogen.
3. Check the total. 90 + 30 = 120 g, which is the full mass of the compound. This confirms it has only carbon and hydrogen, and that both numbers are right.

   % C = 90/120 × 100 = 75, % H = 30/120 × 100 = 25

4. So. The compound is 75% carbon and 25% hydrogen, which is option (d).

The idea to keep. In combustion analysis, multiply the CO₂ mass by 12/44 and the H₂O mass by 2/18. Then check that C and H add up to the sample mass.

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