Question

Question 12.32 An organic compound contains 69% carbon and 4.8% hydrogen, the remainder being oxygen. Calculate the masses of carbon dioxide and water produced when 0.20 g of this substance is subjected to complete combustion.

Class XI Organic Chemistry : Some Basic Principles and Techniques Page 364

Answer 1

Hi

Here is your answer,

% C = 12/44 × mass of CO₂ formed/mass of substance taken × 100

   69 = 12/44 × Mass of CO₂ formed/ 0.2 × 100

 ∴ Mass of CO₂ formed = 69 × 44 × 0.2/12 × 100 = 0.506 g

         %H = 2/18 × mass of H₂O formed/ mass of substance taken × 100

4.8 = 2/18 × Mass of H₂O formed/ 0.2 × 100

∴ Mass of H₂O formed - 4.8 × 18 × 0.2 / 2 × 100 = 0.0864 g

Answer 2

Actually general formula for % of M = {atomic mass of M/molecular mass of M- compound}× {mass of M- compound formed/mass of substance taken}× 100

Use the formula,
% of carbon = (12/44) × {mass of CO2 formed/mass of substance taken } × 100

Here, % of Carbon = 69%
mass of substance taken = 0.2g

69 = (12/44) ×{mass of CO2 formed/0.2g} × 100
mass of CO2 formed = 69 × 44 ×0.2/12 × 100 = 0.506g

now, use the formula,
% of Hydrogen = (2/18)× {mass of H2O formed/mass of substance taken} × 100

Here, % of Hydrogen= 4.8 %
mass of substance taken = 0.2g

4.8 = (2/18) × {mass of H2O formed/0.2} × 100
mass of H2O formed = 4.8 × 18 × 0.2/2 × 100 = 0.0864g