Quantitative Analysis - Kjeldahl’s Method Problem

Description:

Problem

NH₃ obtained when 0.5g of an organic compound substance was subjected to Kjeldahl’s method was neutralized by 10 mL of 1M H₂SO₄. Estimate the composition (percentage) of nitrogen in the given organic compound.

Solution

Given, amount of organic compound taken = 0.5 g

Volume of 1M H₂SO₄ used by NH₃ = 10 mL

Millimoles of H₂SO₄ used = 10 m mol

Millimoles of NH₃ produced = 10mL × 2 = 20 m mol

(As 2 moles of NH₃ neutralize 1 mol of H₂SO₄)

Mass of NH₃ produced = 20 × 10^−3mol × 17

g

/

mol

= 0.34 g

Mass of nitrogen = 0.34 ×

14

/

17

= 0.28

Percentage of N =

0.28

/

0.5

× 100 = 56%

Percentage of N =

1.4 × N_acid × basicity of acid × V_{acid used}

/

Mass of the substance

=

1.4 × 2 × 10

/

0.5

= 56%