Chemistry · Virtual lab
Kjeldahl's Method for Nitrogen Estimation
Digest an organic compound in hot sulfuric acid, distil the ammonia into standard acid, back-titrate the excess, and calculate the percentage of nitrogen.
Background
The Kjeldahl method, developed by Johan Kjeldahl in 1883, is the standard technique for determining the nitrogen content of organic compounds. It is widely used in food science, agriculture, and environmental analysis to measure protein content (since most proteins contain roughly 16% nitrogen).
The method involves three steps: digestion (heating the sample with concentrated sulphuric acid and a catalyst to convert organic nitrogen to ammonium sulphate), distillation (adding excess NaOH to release ammonia gas, which is collected in a known volume of standard acid), and titration (back-titrating the excess acid to determine how much ammonia was absorbed).
In this virtual lab you perform the complete Kjeldahl procedure: weigh the sample, digest it in a Kjeldahl flask, distil the ammonia into standard HCl using a distillation apparatus, and titrate the excess acid to calculate the percentage of nitrogen in the original compound.
What you will learn
- Digest an organic sample with sulphuric acid
- Distil ammonia into a receiver containing standard acid
- Perform a back-titration to determine ammonia absorbed
- Calculate the percentage of nitrogen in the sample
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