QUANTITATIVE ORGANIC ANALYSIS

QUANTITATIVE ORGANIC ANALYSIS

It is used to determine the proportion by weight of elements present in organic compounds:

Carbon and Hydrogen Analysis: 
Weigh a sample of an organic compound and mix it with copper (II) oxide. Place the mixture on a combustion train and heat the mixture between 600 - 800 ^oC. Pass the gases formed into pre-weighed tube containing a drying agent. Here water vapour is absorbed. Pass the remaining gas to another pre-weighed tube containing a strong base such as NaOH or KOH. The increase in weight in each tube gives the weight of the product absorbed. From the weight of the water vapour obtained, the weight and hence the percentage composition of hydrogen in the sample can be determined. Also, from the weight of carbon (IV) oxide absorbed, the weight and percentage of carbon in the sample can determined.

Nitrogen Analysis: this is done by

·        Dumas method: the experimental set-up is somehow similar to that of carbon/hydrogen analysis except that a copper guage is placed in front of the mixture of the sample. CuO and the nitrogen gas produced are collected over NaOH or KOH solution in nitrometer. From the volume of the nitrogen collected, the mass and hence the percentage composition can be determined.

·        Kjeldahl method: in this method nitrogen containing compound is digested with concentrated H₂SO₄ which will give (NH₄)₂SO₄. The solution is made alkaline to liberate ammonia. The amount of ammonia is determined by titration against a standard solution of acid. The weight of nitrogen and percentage of nitrogen in the sample can be determined.