Estimation of Carbon and Hydrogen

Estimation of Carbon and Hydrogen (Liebig's Combustion Method):

Principle: A known mass w gram of organic compound is heated strongly with an excess of dry CuO in a current of dry air or oxygen.

• Carbon oxidised to CO₂ (absorbed by KOH solution)
• Hydrogen oxidised to H₂O (absorbed by anhydrous CaCl₂)

Reactions:

• \[C+2CuO\xrightarrow{\text{strongly heat}}CO_2+2Cu\]
• \[2H+CuO\xrightarrow{\text{strongly heat}}H_2O+Cu\]

Formulas:

\[\%C=\frac{12\times\text{wt of }CO_2}{44\times\text{wt of organic compound}}\times100=\frac{12\times x\times100}{44\times w}=\frac{27.27\times x}{w}\]

\[\%H=\frac{2\times\mathrm{wt~of}H_2O}{18\times\text{wt of organic compound}}\times100=\frac{2\times y\times100}{18\times w}=\frac{11.11\times y}{w}\]

Where x = mass of CO₂ absorbed, y = mass of H₂O absorbed, and w = mass of organic compound.