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1.56g of a coal sample was kjeldahlised and $NH_3$ gas thus evolved was absorbed in 50ml of 0.1N $H_2 SO_4$

after absorption the excess acid required 6.25ml of 0.1N NaOH for exact neutralization. Calculate the percentage of N in the coal sample.

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Weight of coal sample = 1.56 gm

$NaOH$ consumed = 6.5 ml

Normality of $H_2SO_4$ and $NaOH$ = 0.1N

Quantity of $H_2SO_4$ used = 50ml

Amount of $H_2SO_4$ used = (50 - 6.5) = 43.5ml

$\begin{aligned} N \% &= \text{Volume of acid consumed} \times \text{Normality of acid} \times \text{1.4 / weight of coal sample} \\ &=43.5 \times 0.1 \times 1.4 / 1.56 \\ &= 3.9 \% \end{aligned}$

Answer: N% = 3.9%

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