Calculate percentage of nitrogen in ammonium sulphate by kjehdal method
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One mole of ammonia coming from the digestion mixture (and hence from the original protein) will neutralize exactly one mole of the acid in the trapping flask.
The first calculation, therefore, is to find the number of moles of ammonia that have been produced and then trapped from your sample(s).
This is done by,
calculating the number of moles of acid in the trapping flask originally (before any ammonia was trapped) by multiplying the molarity of the acid solution by the volume of the trapping solution
moles of acid =
molarity of acid x volume used in flask
(molesA = M x V)calculating the number of moles of base (NaOH) that were added from the buret to neutralize the remaining acid (that NOT neutralized by the ammonia).moles of base =
molarity of base x volume added from buret
(molesB = M x V)subtracting the "moles of base" added from the "moles of acid" present at the beginning, to get,the number of "moles of ammonia" coming from the protein,the number of "moles of ammonia" is the same as the "moles of nitrogen",so ... to calculate the number of grams of nitrogen in the original sample of protein, multiply the "moles of nitrogen" by the atomic mass of nitrogen (mass of atoms of nitrogen),
gms nitrogen =
moles nitrogen x atomic mass
(gN = molesN x 14.0067)
It is also possible to calculate the amount of crude protein in the sample. Although there are differences between different samples, the amount of "crude protein" (CP) can be found by multipling the percent Nitrogen by a factor (usually 6.25).
CP = %N x 6.25percent Nitrogen
The percentage of nitrogen found in the orginal sample can now be calculated by:
%nitrogen =
(gms nitrogen / gms sample) x 100
%N = (gN / gS) x 100
One mole of ammonia coming from the digestion mixture (and hence from the original protein) will neutralize exactly one mole of the acid in the trapping flask.
The first calculation, therefore, is to find the number of moles of ammonia that have been produced and then trapped from your sample(s).
This is done by,
calculating the number of moles of acid in the trapping flask originally (before any ammonia was trapped) by multiplying the molarity of the acid solution by the volume of the trapping solution
moles of acid =
molarity of acid x volume used in flask
(molesA = M x V)calculating the number of moles of base (NaOH) that were added from the buret to neutralize the remaining acid (that NOT neutralized by the ammonia).moles of base =
molarity of base x volume added from buret
(molesB = M x V)subtracting the "moles of base" added from the "moles of acid" present at the beginning, to get,the number of "moles of ammonia" coming from the protein,the number of "moles of ammonia" is the same as the "moles of nitrogen",so ... to calculate the number of grams of nitrogen in the original sample of protein, multiply the "moles of nitrogen" by the atomic mass of nitrogen (mass of atoms of nitrogen),
gms nitrogen =
moles nitrogen x atomic mass
(gN = molesN x 14.0067)
It is also possible to calculate the amount of crude protein in the sample. Although there are differences between different samples, the amount of "crude protein" (CP) can be found by multipling the percent Nitrogen by a factor (usually 6.25).
CP = %N x 6.25percent Nitrogen
The percentage of nitrogen found in the orginal sample can now be calculated by:
%nitrogen =
(gms nitrogen / gms sample) x 100
%N = (gN / gS) x 100
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