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 :
NH3 (aq) + HCl (aq) <= > NH4Cl
From the above equation, we see that each mole of HCl reacts completely with 1 mole of NH3 during titration.
Therefore, no. of moles of NH3 that would have been neutralized by 0.001185 moles of HCl = 0.001185 moles
From the formula of NH3 , 1 mole of NH3 contains 1 mole of N atoms.
Therefore, nº of moles of :
N - atoms present = 0.001185 moles
Moar mass of N= 14 g/mol
Mass of 0.001185 moles of N =0.001185 moles * 14 g/ mol
= 0.01659 g
% of N in protein is given as 16%.
16%.of mass of protein = mass of nitrogen in protein sample = 0.01659 g
(16/100) *mass of protein = 0.01659 g
mass of protein = 0.1036875 g
% of protein in potato flour = [mass of protein in potato flour / mass of potato flour] * 100%
( 0.1036875 g / 5.724 ) * 100%
= 1.812 %
Hope this helps!
