Quantitative Analysis - Nitrogen Kjeldahl’s Method II
Description:
Percentage of Nitrogen
Let the mass of the organic compound = m g
Volume of H2SO4 of molarity M taken = V mL
Volume of NaOH of molarity M used for titration of excess/unused acid = V1 mL
Titration reaction: 2NaOH + H2SO4 → Na2SO4 + 2H2O
According to molarity relation, MV1 =
MV2
2
V1 mL of NaOH of molarity M =
V1
2
mL of H2SO4 of molarity M
Volume of unused H2SO4 = V -
V1
2
mL
(V -
V1
2
) mL of H2SO4 of molarity M = 2(V -
V1
2
) mL of NH3 solution of molarity M.
1000 mL of 1M NH3 contains 17 g of NH3 or 14 g of nitrogen.
2(V -
V1
2
) mL of NH3 solution of molarity M contains −
14 × M × 2(V -
V1
2
)
1000
Percentage of N =
14 × M × 2(V -
V1
2
)
1000
×
100
m
=
1.4 × M × 2(V -
V1
2
)
m
Percentage of N =
1.4 × M × 2(V -
V1
2
)
m
Or Percentage of N =
1.4 × Nacid × basicity of acid × Vacid used
Mass of the substance