Quantitative Analysis - Halogens with Example

Description:

In a special type of tube called Carius tube, organic compound is heated with fuming nitric acid in the presence of silver nitrate.

Carbon and hydrogen are oxidized to CO₂ and H₂O.

The halogen is converted to corresponding silver halide (AgX).

It is filtered, washed, dried and weighed.

Let the mass of an organic compound = m g

• Mass of AgX formed = m₁ g

• 1 mol of AgX contains 1 mol of X

• Mass of halogen in m₁ g of AgX =

  atomic mass of X × m₁g

  /

  molecular mass of AgX

Percentage of halogen =

atomic mass of X × m₁ × 100

/

molecular mass of AgX × m

Note − Carius method does not give satisfactory results for the estimation of iodine, as Agl is slightly soluble in HNO₃.

Problem

0.20 g of organic compound is subjected to Carius Method for the estimation of halogen and resulted in 0.15 g of AgBr. Determine the percentage of bromine in the given organic compound.

Solution

Given, mass of organic compound = 0.20 g

molar mass of AgBr = 108 + 80 = 188 g/mol

188 g of AgBr contains − 80 g bromine

Thus, 0.15 g of AgBr contains =

80 × 0.15

/

188

= 0.063 g bromine

Percentage of bromine =

0.063 × 100

/

0.20

= 31.5 %