8. The protein in a 1.2846-g sample of an oat cereal is determined by a Kjeldahl analysis. The sample is digested with H2SO4, the resulting solution made basic with NaOH, and the NH3 distilled into 50.00 mL of 0.09552 M HCl. The excess HCl is back titrated using 37.84 mL of 0.05992 M NaOH. Given that the proteins in grains average 17.54% w/w N, report the %w/w protein in the sample.

The %w/w protein in the sample is 15.2 %

Explanation:

To calculate the number of moles for given molarity, we use the equation:

According to stoichiometry :

1 mole of require 1 mole of

Thus 0.0023 moles of will require=  of

moles of HCl used = (0.0047-0.0023) = 0.0024

1 mole of HCl uses = 1 mole of ammonia

Thus 0.0024 moles uses = of ammonia

Mass of ammonia=

17 g of ammonia contains = 14 g of Nitrogen

Thus 0.0408 g of ammonia contains = of Nitrogen

Now 17.45 g of Nitrogen is present in = 100 g of protein

Thus 0.034 g of Nitrogen is present in = of protein

Now % w/w of protein =

Thus %w/w protein in the sample is 15.2%