Liebig method (carbon and hydrogen estimation) (%C = (12/44) × (mass of CO₂/mass of compound) × 100; %H = (2/18) × (mass of H₂O/mass of)
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%C = (12/44) × (mass of CO₂/mass of compound) × 100; %H = (2/18) × (mass of H₂O/mass of compound) × 100
What each symbol means
| Symbol | What it stands for |
|---|---|
| W | Mass of organic compound (g) |
| 2/18 | Fraction of H in H₂O (2 × atomic mass H / molar mass H₂O) |
| 12/44 | Fraction of C in CO₂ (atomic mass C / molar mass CO₂) |
| m_CO₂ | Mass of CO₂ absorbed by KOH (g) |
| m_H₂O | Mass of H₂O absorbed by CaCl₂ (g) |
When to use this
Compound burned with excess CuO in combustion tube. Products pass through CaCl₂ tube (absorbs H₂O) THEN KOH bulb (absorbs CO₂). Order matters: CaCl₂ first, else KOH absorbs both H₂O and CO₂. For compounds containing N, reduced Cu gauze is placed at the exit to reduce NOₓ to N₂. For halogen-containing compounds, Ag gauze traps HX as AgX.