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 NH_3(aq) + HCI (aq) rightarrow NH_4CI(aq) If 16.0 mL of 0.150 M HCI (aq) is needed to neutralize all the NH_3(g) from a 2.25-g sample of organic material, calculate the mass percentage of nitrogen in the sample.

Explanation / Answer

NH3(aq) + HCl(aq) ----> NH4Cl(aq)

no of mole of HCl = M*V

                = 16*0.15

                = 2.4 mmole
from equation

no of mole of HCl = no of mole of NH3

no of mole of NH3 = no of mole of N present in sample

no of mole of N present in sample = 2.4 mmole

mass of N present in sample = n*mwt

           = 2.4*10^-3*14

           = 0.0336 g

% of N in sample = 0.0336/2.25*100 = 1.49%

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