Describe the estimation of nitrogen by Dumas method.

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Solution

Dumas Method:- When nitrogen organic compound is heated with excess copper oxide in an atmosphere $C O_{2}$ , free nitrogen is obtained in addition to $C O_{2}$ and water. Chemical reactions are:

$C + 2 C u O ⟶ C O_{2} + 2 C u$
$2 H + C u O ⟶ H_{2} O + C u$

$N i t r o g e n$ + $C u O ⟶ N_{2} + O x i d e s o f n i t r o g e n$
$O x i d e s o f n i t r o g e n + C u ⟶ N_{2} + C u O$

The mixture of gases is collected over $K O H$ solution that absorbs $C O_{2}$

Percentage of Nitrogen:

$22, 400 c m^{3}$ of Nitrogen= $28 g$ [at STP]
$V_{2} c m^{3}$ of Nitrogen= $\frac{28 V_{2}}{22400}$

Amount of nitrogen in "m" g of compound
= $\frac{28 V_{2}}{22400 m}$
$\Rightarrow$ % of Nitrogen= $\frac{28 \times V_{N_{2}} \times 100}{22400 \times m}$

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Differentiate between the principle of estimation of nitrogen in an organic compound by (i) Dumas method and (ii) Kjeldahl’s method.

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