Question

In the Kjeldahl's method for estimation of nitrogen present in a soil sample, ammonia evolved from $0.75\, g$ of sample neutralized $10\, mL$ of $1 \, M \, H_2SO_4$. The percentage of nitrogen in the soil is :

• A. 37.33
• B. 45.33
• C. 35.33
• D. 43.33

Answer 1

Answer: (A)

$\because M \times V(m l)=m$ mol
$10 \,m \,mol\, H _2 SO _4=20 \,m$ mol of $NH _3$
$\left[ H _2 SO _4+2 NH _3 \longrightarrow\left( NH _4\right)_2 SO _4\right]$
$1\, mol\, NH _3$ contains $14 \,g$ nitrogen
$20 \times 10^{-3}$ mol $NH _3$ contains $14 \times 20 \times 10^{-3}$ nitrogen
$0.75\, g$ of sample contains
$\%$ Nitrogen $=\frac{14 \times 20 \times 10^{-3}}{0.75} \times 100=37.33 \%$