Question

In Kjeldahi's method for the estimation of nitrogen present in a soil sample, the ammonia evolved from $0.75\text{g}$ of the sample was neutralised by $10\text{mL}\text{of}1\text{M}$ $H_{2}S{O}_4$. Find the percentage of nitrogen in the soil sample.

• A. $37.33\%$
• B. $35.33\%$
• C. $45.33\%$
• D. $43.33\%$

Answer 1

The correct option is A $37.33\%$

Volume of $H_{2}S{O}_4$ used = $10\text{mL}\text{of}1\text{M}$ $H_{2}S{O}_4$
$1\text{mol}\text{of}$ $H_{2}S{O}_4$ reacts with $2\text{mols}$ of $N{H}_3$
Therefore, $10\text{mL}\text{of}1\text{M}$ $H_{2}S{O}_4=20\text{mL}of1\text{M}N{H}_3$
Now,
$1000\text{mL of}1\text{M}N{H}_3\text{contain}N=14\text{g}$
Therefore,
$20\text{mL of}1\text{M}N{H}_3\text{will contain}N=\frac{14}{1000}\times 20$
$\therefore \text{percentage of nitrogen}=\frac{14\times 20\times 100}{1000\times 0.75}=37.33\text{\%}$
Thus, option (a) is the correct answer.