Question 1.7.2.4: 1.56 g of a coal sample was Kjehldahlised and NH3 gas thus e......
1.56 g of a coal sample was Kjehldahlised and NH_{3} gas thus evolved was absorbed in 50 mL of 0.1 N H_{2}SO_{4}. After absorption, the excess (residual) acid required 6.25 mL of 0.1 N NaOH for exact neutralisation. Calculate the percentage of nitrogen in the coal sample.
Weight of coal sample taken = 1.56 g
Since 6.25 mL of 0.1N NaOH is used for neutralisation, excess acid
= 6.25 mL of 0.1 N H_{2}SO_{4}.
Therefore, volume of H_{2}SO4used to neutralise NH_{3} evolved
= 50 mL of 0.1 N H_{2}SO_{4}– 6.25 mL of 0.1 N H_{2}SO_{4}
= (50–6.25)× 0.1 N H_{2}SO_{4}
= 43.75 mL of 0.1 N H_{2}SO_{4}
Percentage of nitrogen = \frac{Volume of H_{2 }SO_{4} used × normality of H_{2 }SO_{4}\times 1.4 }{1.56}= 3.926%
\frac{43.75\times 0.1 \times1.4}{1.56}= 3.926
Percentage of nitrogen = 3.926%