Quantitative Analysis Of Organic Compounds

Quantitative analysis is an analysis method used to determine the quantity of elements or molecules produced during the reaction.  Organic compounds consist of carbon and hydrogen. It also consists of oxygen, nitrogen, phosphorus, sulphur and halogens. The various methods used for the measurement of percentage composition of elements in an organic compound are explained below:

Quantitative analysis of halogens:

  1. Carius method: A mixture of organic compound and fuming nitric acid is heated in the presence of silver nitrate contained in a tube (hard glass) known as Carius tube in a furnace. Carbon and hydrogen present in the organic compound are oxidized to carbon dioxide and water respectively. The halogens present in the organic compound reacts with the silver nitrate to from the corresponding silver halide (AgX). After this it is filtered, washed, dried and weighed.

 

Calculations:

Let the mass of the given organic compound be m g.

Suppose mass of AgX formed = m1 g.

We know that 1 mol of AgX consists of 1 mol of X.

So, in m1 g of AgX , mass of halogen = \( \frac {(atomic~mass~of~X~×~m_1~g)}{(molecular~mass~of~AgX)}\)

Percentage of halogen = \( \frac {(atomic~mass~of~X~×~m_1~×~100)}{(molecular~mass~of~AgX~×~m)}\)

Quantitative analysis of sulphur:

A fixed mass of an organic compound containing sulphur is heated in a Carius tube containing sodium peroxide or fuming nitric acid. Sulphur present in the organic compound is oxidized to sulphuric acid. It is then precipitated as barium sulphate by the addition of barium chloride solution in water. The precipitate is then washed, filtered, dried and weighed. The mass of barium sulphate is used in calculating the percentage of sulphur in the given organic compound.

Quantitative analysis

 

Calculations:

Suppose the mass of organic compound = m g.

Let the mass of barium sulphate formed = m1 g.

We know that 32 g sulphur is present in 1 mol of BaSO4

Therefore, 233 g BaSO4 contains 32 g sulphur

  • ⇒   M1 g of BaSOcontains \( \frac {32~×~m_1}{233} g \)  of sulphur

Percentage of sulphur = \( \frac {32~×~m_1~×~100}{233~×~m}\)

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