Estimation of Carbon & Hydrogen in Organic Compounds

Both carbon and hydrogen are estimated in one experiment. A known mass of an organic compound is burnt in the presence of excess of oxygen and copper(II) oxide. Carbon and hydrogen in the compound are oxidized to carbon dioxide and water respectively.

C_xH_y + (x+y/4) O₂ → x CO₂ + (y/2) H₂O

The mass of water produced is determined by passing the mixture through a weighed U-tube containing anhydrous calcium chloride. Carbon dioxide is absorbed in another U-tube containing concentrated solution of potassium hydroxide.

The increase in masses of calcium chloride and potassium hydroxide gives the amounts of water and carbon dioxide from which the percentages of carbon and hydrogen are calculated.

Let the mass of organic compound be m g, mass of water and carbon dioxide produced be m₁ and m₂ g respectively.

Percentage of carbon = (12 x m₂ x 100)/(44 x m) 

Percentage of hydrogen = (2 x m₁ x 100)/(18 x m)