Bleaching powder is not a true compound but
it is a mixed salt of calcium hypochlorite [Ca (OCl)
2].3H2O and basic calcium chloride [CaCl2Ca (OH) 2H2O]. [Simply
it is represented by CaOCl2.
The bleaching action of [CaOCl2] is due to liberation of oxygen with limited quantity of dilute acid.
Whereas disinfectant action available of Cl2 on reaction with excess of acid.
The bleaching action of [CaOCl2] is due to liberation of oxygen with limited quantity of dilute acid.
The Chlorine liberates is called available
Chlorine, and calculation of available Chlorine is called IODOMETRY.
IODOMETRIC-CALCULATION OF AVAILABLE
% CHLORINE: Take a W (gm)
sample of bleaching powder; and when bleaching powder treated with dilute acid or water then liberates chlorine gas.
The chlorine produced in above reaction is titrated with
KI solution which produced (I2) Iodine which is further completely titrated
with hypo solution.
If number of millimoles of hypo solution consume is M V
then millimoles of %available chlorine is calculated as ;
Millimoles of
Iodine is =1/2 Millimoles Hypo solution
Millimoles of
Iodine is = Millimoles chlorine
Weight of available chlorine is = Number of
moles x molecular Wt of Chlorine
ILLUSTRATIVE EXAMPLE(1): If
trace of chlorine are not remove from pulp used for paper manufacturing , then
on the long standing it weaken the paper and makes it yellowish , which of
following antichlor can be used to remove chlorine from pulp ?.
(A) Na2S2O3 (B) conc. HCl (C) NaHCO3 (D) Both (A) and (B)
(A) Na2S2O3 (B) conc. HCl (C) NaHCO3 (D) Both (A) and (B)
SOLUTION:
An antichlor is a substance used
to decompose residual hypochlorite or chlorine after use of chlorine based
bleaching , in order to prevent ongoing reactions .example s of antichlor –
Sodiumbisulphite (NaHSO3),
Pottassiumbisulphite (KHSO3) , Sodiummetasulphite (Na2S2O3),
Sodiumthiosulphate (Na2S2O3) and
hydrogen peroxide (H2O2).
ILLUSTRATIVE EXAMPLE (2): Available
chlorine in sample of bleaching powder can be calculated as per the
following reactions.
If 4 gm of bleaching powder dissolved to give 100 ml
solution 25 ml of it react with excess of CH3COOH and KI .The Iodine
liberation required 10 ml of 0.125 N Hypo solutions. Calculate % of available
chlorine in the sample.
(A) 21% (B) 35 % (C) 45 % (D) 4.4%
(A) 21% (B) 35 % (C) 45 % (D) 4.4%
SOLUTION:
ILLUSTRATIVE EXAMPLE (3): Calculate
the % of available chlorine in the sample in a sample of 3.35 gm of bleaching
powder which was dissolved to 100 ml water. 25 ml of this solution on treatment
react with KI and dilute acid. Required 20 ml 0.125 N Hypo solution (Sodiumthiosulphate- Na2S2O3).
SOLUTION:
ILLUSTRATIVE EXAMPLE (4): 25 ml of household bleach solution was mixed with 30 ml of 0.50 M KI and 10 ml of 4.0N acetic acid. In this titration of the liberated iodine 48 ml of 0.25 N Na2S2O3 was used to reach the end point. The Molarity of household bleach solution is?
SOLUTION:
SOLUTION:
