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) 50.0 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. Number 0

Explanation / Answer

mmol of HCl = MV = 50*0.150 = 7.5 mmol

mmol of NH3 = 7.5

mmol of N = 7.5

mass of N = 7.5*14 = 105 mg of N

% N = (105*10^-3)/(2.25)*100 = 4.6666% N

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