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 32.0 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

If 29.0 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.

NH3+ HCl ==>NH4Cl

moles of NH3 produced from Nitrogen=moles of HCl Consumes (since they react 1:1)

Moles of HCl=0.15moles/L*0.029L=0.00435moles

moles of Nirogen=0.00435moles

mass f nitrogen=moles*molar mass=0.00435moles*14g/mole=0.0609g

mass of sample taken=2.25g

mass %age of Nitrogen=mass of N/total mass of sample*100=0.0609g/2.25g*100=2.71%

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