Question

Bleaching powder is a mixed salt of hydrochloric acid and hypochlorous acid. It has the formula,
CaOCl2.H2O. It is manufactured by the action of chlorine on dry slaked lime at 40oC. There is also a view
that bleaching powder is a mixture of calcium hypochlorite and basic calcium chloride
[Ca(OCl)2+CaCl2Ca(OH)2.H2O].
The amount of chlorine obtained from a sample of bleaching powder by the treatment with excess of
dilute acids or CO2 is called available chlorine. A good sample of bleaching powder contains 35-38% of
available chlorine. On long standing , it undergoes auto-oxidation and the amount of available chlorine
decreases.
The estimation of available chlorine is done volumetrically by (a) iodometric method or by (b) arsenite
method.
In textile industry, the cotton cloth is mainly bleached with the help of bleaching powder.
12. Maximum percentage of available chlorine on the basis of CaOCl2.H2O formula is:
(A) 35 (B) 40
(C) 45 (D) 49
13. The percentage of available chlorine in commercial samples of bleaching powder is usually
between 33- 38%. The low value is due to:
(A) incomplete reaction between slaked lime and Cl2 during its formation
(B) impurities present in the original slaked lime
(C) decomposition of bleaching powder when kept in air
(D) all of the above
14. 3.55g of bleaching powder when treated with acetic acid and excess of Kl liberated iodine which
required 60mL of 0.5N sodium thiosulphate solution. The percentage of available chlorine in the
sample is:
(A) 30.0 (B) 25.0
(C) 20.0 (D) 35.0
15. On long standing, the bleaching powder undergoes auto-oxidation. The products formed are:
(A) calcium chloride only (B) calcium chlorate only
(C) calcium chloride and calcium chlorate (D) calcium chloride and calcium chlorite
16. The chemical name of bleaching powder is:
(​(A) calcium hypochlorite (B) calcium chlorohypochlorite
(C) calcium chlorate (D) calcium perchlorate

Answer 1

12. Maximum percentage of available chlorine on the basis of CaOCl₂.H₂O formula is
​CaOCl₂ .2 H₂O $\to$ Cl​₂

145 g $\to$ 71 g
% of available chlorine is = $\frac{71}{145}\times 100$ = 48.9 % = 49%


13. The percentage of available chlorine in commercial samples of bleaching powder is usually
between 33- 38%. The low value is due to:
Ans : D all the above

14. 3.55g of bleaching powder when treated with acetic acid and excess of Kl liberated iodine which
required 60 mL of 0.5N sodium thiosulphate solution. The percentage of available chlorine in the
sample is:

% of available Chlorine =$\frac{3.55\times M\times V}{W}$ = $\frac{3.55\times 0.5\times 60}{3.55}$ = 30 %

15. On long standing, the bleaching powder undergoes auto-oxidation. The products formed are:

Bleaching powder oxidises to calcium chlorate and calcium chloride

6 CaOCl₂ $\to$Ca(ClO_​3)₂ + 5 CaCl₂

16. The chemical name of bleaching powder is:
calcium hypochlorite - CaOCl₂