Question

Estimation of halogens in organic compound is done by

Answer 1

The Carius halogen method in analytical chemistry is a method for the quantitative determination of halogens in chemical substances. A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as carius tube, in a furnace.

Answer 2

Estimation of halogen

Estimation of hologen is done by following two methods

(1) Carius Method (2) Piria & Schiff’s method

1) Carius Method

In this method organic compound containing halogen is heated in a carius tube with F HNO3 in presence of AgNO3, Silver halide (AgX) is precipitated. By Knowing the wt. of silver halide & organic Compound percentage of halogens can be calculated (x=-Cl, -Br,-I)

Calculation –

wt. of organic compound (o.c.) = w gm

wt. of AgCl= x gm

Mol. wt. of AgCl=108+35.5 = 143.5

143.5 gm of AgCl contain Cl = 35.5 gm

x gm of AgCl contain Cl =35.5 x /143.5

w gm of o. c .contains Cl = 35.5 x /143.5

100 gm of o. c .contains Cl =[( 35.5 x) 100 ] / (143.5 w)

% of Cl = (35.5 x wt.of AgCl x 100) /( 143.5 x wt. of o.c.)

General Formula

% of X= (At.wt. of X x wt.of AgX x 100) /( mol.wt. of AgX x wt. of o.c.)

At. wt of Br= 80

Molecular weight of AgBr = 108+80= 188

% of Br =(80 x wt.of AgBr x 100) /( 188 x wt. of o.c.)

Atomic weight of Iodine = 127

Molecular weight of AgI = 108+127=235

% of I= (127 x wt.of AgI x 100) /( 235 x wt. of o.c.)

Piria & Schiff’s Method-

Known amount of organic compound is fused with CaO+Na2CO3 in Pt or Ni crucible. The product obtained is dissolved in excess of HNO3 & halogen is precipitated with AgNO3 Soln in the form of AgX. By knowing the wt. of o.c . & AgX, We can calculate the % of halogen.

Q 1) 0.185 gm of organic compound gave 0.319 gm AgBr. Calculate the % of Br?

Solution : wt.of AgBr =0.319 gm.

weight of o.c. =0.185 gm.

% of Bromine =(80 x wt.of AgBr x 100) /( 188 x wt. of o.c.)

percentage of Br = (80 x 0.319 x 100) /( 188 x 0.185)

% of Br =73.36 % Ans.

Q 2) 0.156 gm of o. c. on heating with f HNO3 & AgNO3 gives 0.235 gm of AgI. Calculate % of I.

Solution : wt. of AgI=0.235 gm.

weight of o.c.=0.156 gm.

% of Iodine= (127 x wt.of AgI x 100) /( 235 x wt. of o.c.)

percentage of I= (127 x 0.235 x 100) /( 235 x 0.156)

% of I = 81.41 % Ans.

Q 3) 0.1170 gm of an o.c on heating with conc. HNO3 & AgNO3 in carius tube gave 0.42 gm of AgCl. Find the percentage of Cl ?

Ans. wt.of AgCl =0.42 gm.

wt. of o.c.= 0.1170 gm.

percentage of Cl = (35.5 x wt.of AgCl x 100) /( 143.5 x wt. of o.c.)

= (35.5 x 0.42 x 100) /( 143.5 x 0.1170)

% of Chlorine = 88.80 % Ans.

Q 4) 1.09 gm of an organic compound on combustion gave 0.88 gm of CO2 & 0.45 gms. of H2O . 0.218 gm of this compound on heating with f HNO3 & AgNO3 gave 0.376 gm of AgBr. Calculate the % of C, H & Br.

Ans. wt. of CO2 =0.88 gm.

weight of o.c. =1.09 gm.

% of Carbon =(12 x wt.of CO2 x 100) /( 44 x wt. of o.c.)

percentage of C =(12 x 0.88 x 100) /( 44 x 1.09)

% of C =22.01 % Ans.

percentage of H =(2 x wt.of H2O x 100) /( 18 x wt. of o.c.)

=(2 x 0.45 x 100) /( 18 x 1.09)

% of H =4.58 % Ans.

percentage of Br =(80 x wt.of AgBr x 100) /( 188 x wt. of o.c.)

=(80 x 0.376 x 100) /( 188 x 0.218)

% of Bromine=73.39 Ans.