On complete combustion, 0.492 g of an organic compound gave 0.792 g of CO₂. The % of carbon in the organic compound is ___________ (Nearest integer)

Solution

Chemistry ma’am · 4 steps

Every carbon atom ends up in CO₂, so take carbon's share of that CO₂ mass.

1. Carbon goes to CO2. On complete combustion all the carbon in the compound turns into CO₂. In 44 g of CO₂ there is 12 g of carbon, so carbon is 12/44 of the CO₂ mass.

   % C = 12/44 × (mass of CO₂)/(mass of compound) × 100

2. Mass of carbon. Mass of C = 12/44 × 0.792 = 0.216 g. This is the carbon that was in the 0.492 g sample.
3. Percentage. % C = 0.216/0.492 × 100 = 43.9.
4. So. The compound is 43.9% carbon, which rounds to 44.

The common slip: 27. Dividing the carbon mass by the mass of CO₂ instead of the compound gives 27, which is only carbon's share of CO₂.

The idea to keep. In combustion analysis, find the element's mass from its product first: 12/44 of the CO₂ for carbon, 2/18 of the H₂O for hydrogen. Then divide by the sample mass.

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