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1.56g of coal sample was kjeldahlished and `NH_3` gas thus evolved was absorbed in 50ml of 0.1N `H_2SO_4`. After absorption to excess (residual) acid requires 6.25ml of 0.1N NaOH for exact neutralisation. Calculate the percentage of N in the coal sample.

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#### Solution

Calculation of Nitrogen percentage

Weight of coal = 1.56gm

Volume of H_{2}SO_{4} = 50 ml

Volume of NaOH = 6.25 ml

Normality of H_{2}SO_{4} and NaOH = 0.1 N

H2SO4 consumed = 50-6.25 = 43.75 ml

Equivalent of H2SO4 = 43.75*0.1

= 4.375 * 10^{-3} milli equivalent

N2 = 4.375 * 10^{-3} * 14

= wt. of nitrogen / wt. of coal sample * 100

= 4.375 * 10^{-3} *14 / 1.56 *100

= 3.93 %

Concept: Solid Fuels

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