Question

Give the principle involved in the estimation of halogen in an organic compound by Carius method.

Answer 1

Estimation of halogens (Carius method):
A known mass of the organic compound is heated with fuming HNO₃ along with AgNO₃. C, H & S gets oxidized to CO₂, H₂O, SO₂ and halogen combines with AgNO₃ to form a precipitate of silver halide.

\[\ce{X ->[fum.HNO3][AgNO3] AgX↓}\]

The ppt of AgX is filtered, washed, dried and weighed. From the mass of AgX and the mass of the organic compound taken, percentage of halogens is calculated.

The ppt of AgX is filtered, washed, dried and weighed. From the mass of AgX and the mass of the organic compound taken, percentage of halogens is calculated.

Calculation:

Weight of the organic compound: w g

Weight of AgCl precipitate = a g

143. 5 g of AgCl contains 35.5 g of Cl

∴ a g of AgCl contains `(35.5)/(143.5) xx "a"`

w g Organic compound gives a g AgCl

Percentage of Cl in w g organic compound = `((35.5)/(143.5) xx "a"/"w" xx 100)%`

Let Weight of silver Bromide be ‘b’ g

188 g of AgBr contains 80 g of Br

∴ w g of AgBr contains `80/180 xx "b"/"w"` of Br

w g Organic compound gives b g AgBr

Percentage of Br in w g organic compound = `(80/180 xx "b"/"w" xx 100)`%

Let Weight of silver Iodide be ‘c’ g

235 g of AgI contains 127 g of I

∴ C g of AgI contains `(127/235 xx "c"/"w")`of I

w g Organic compound gives c g AgI

percentage of I in w g organic compound = `(80/180 xx "b"/"w" xx 100)`%