The amount of nitrogen in an organic substance can be determined by an analytica

Question

The amount of nitrogen in an organic substance can be determined by an analytical method called the Kjeldahl method, in which all the nitrogen in the organic substance is converted to ammonia. The ammonia, which is a weak base, can be neutralized with hydrochloric acid, as described by the equation: NH3(aq)+HCl (aq)--> NH4Cl(aq).If 93.0 mL of 0.150 M HCl(aq) is needed to neutralize all the NH3(g) from a 2.25-g sample of organic material, calculate the mass percentage of nitrogen in the sample.

Explanation / Answer

mol of HCl = MV= 93*0.15 =13.95 mmol of H+ used

so..

ratio is 1:1

13.95 mmol of H = 13.95 mmol of NH3

13.95 mmol of NH3 = 13.95 mmol of N

mass of N = (13.95*10^-3)(14) = 0.1953g of N

total sample = 2.25

% N in sample = 0.1953/2.25 *100 = 0.0868 * 100% = 8.68% is N

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