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 ) + HCl ( aq ) ⟶ NH 4 Cl ( aq ) If 35.0 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.

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, (aq) + HCl(aq) + NH4Cl(aq) If 35.0 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. mass percentage:

Answer 1

Given that

equation NH 3 ( aq ) + HCl ( aq ) ---- > NH 4 Cl ( aq )

35.0 mL of 0.150 M HCl ( aq )

Sample mass= 2.25 g sample

Number of moles = molarity *volume in L

HCl moles = 0.150*35/1000

= 0.00525 moles HCl

Now calculate the moles of NH3:

0.00525 moles HCl *1/1

=0.00525 moles NH3

1 mole NH3 will give 1 mole N

So, 0.00525 moles NH3 will give 0.00525 mole N

Amount in g = number of moles * molar mass

= 0.00525 mole N*14.0067 g/ mole

= 0.0735 g

% of N = mass of N / sample mass *100

=0.0735 g /2.25 g sample *100

= 3.27%