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 add. as described by the equation NH_3(aq) + HCI(aq) rightarrow NH_4Cl(aq) If 59.0 mL of 0.150 M HCl(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

From the equation it is clear that 1 mole of HCl neutralizes 1 mole of NH3
59 mL of 0.150M HCl contains 0.059 x 0.15 = 0.0089 moles of HCl
The molecular mass of N is 14.00 g/mol so there were 0.0089 x 14.00 = 0.125 g of N in the original sample NH3 of 2.25 g.

The mass percentage therefore is (0.125/2.25) x 100 = 5.56%

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