Estimation of halogens

Estimation of halogen

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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.)

2. 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 HNO_{3 &} 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.