Question

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. 

Answer 1

Calculation of Nitrogen percentage
Weight of coal = 1.56gm 

Volume of H₂SO₄ = 50 ml
Volume of NaOH = 6.25 ml
Normality of H₂SO₄ 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 %