You carefully weigh 5.724 g of potato flour into a Kjeldahl flask and add an appropriate reagent to digest the flour. You then c

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You carefully weigh 5.724 g of potato flour into a Kjeldahl flask and add an appropriate reagent to digest the flour. You then c

arefully distill the material by adding a reagent to the digestion flask and stirring vigorously, then heating while under a closed system. You collect distillate in a collection flask containing a liquid, then titrate with 0.1 N HCl. It takes 11.95 ml to titrate the sample. The volume of titrate for blank titration is 0.1 ml. What was the percent protein in the potato flour if the protein in potato flour is 16% nitrogen?

Chemistry

1 answer:

Llana [10] · Answer 1 · 2022-03-16T20:14:36+03:00

Hey there!:

In Kjeldahl's method estimation of amount of nitrogen in a sample, the sample is first digested by using sulphuric acid , which converts the nitrogen in the sample to ammonium sulphate.

The ammonium ions in the digested product are converted to ammonia gas by adding excess of base like NaOH. The ammonia gas thus produced is collected by condensation.

The amount of ammonia produced is estimated by titration with standard solution of acid. We are using 0.1 N HCl in this case.

Volume of 0.1 N HCl used = 11.95 mL

Volume of of 0.1 N HCl used in blank titration =0.1 mL

Therefore,actual volume us of 0.1 N HCl

used by analyte( ammonia solution) = 11.95 mL - 0.1 mL

= 11.85 mL

0.1 N HCl = 0.1 M HCl , as HCl is a monobasic acid and therefore its molar mass will be equal to its equivalent mass.

Therefore, concentration of HCl solution used = 0.1 M = 0.1 mol L-1

Volume of HCl solution used =11.85 mL =0.01185 L

Nº.of moles of HCl used = 0.1 mol L-1 * 0.01185 L

= 0.001185 moles

The equation for reaction between NH3 (aq) and HCl during titration is :