Class 11 Chemistry Notes Stocihiometry – Calculation of Chlorine from a Sample of Bleaching Powder

The weight % of available Cl₂ from the given sample of bleaching powder on reaction with dil acids or CO₂ is called available chlorine.

CaOCl₂ + H₂SO₄ → CaSO₄ + H₂O + Cl₂
CaOCl₂ + 2HCl → CaCl₂ + H₂O + Cl₂
CaOCl₂ + 2CH₃COOH → Ca (CH₃COO) ₂ + H₂O + Cl₂
CaCOl₂ + CO₂ → CaCO₃ + Cl₂

Method of determination:

Bleaching powder + CH₃COOH + KI (starch/Hypo)end point
Meq. Of I₂ = Meq. Of Cl₂ = Meq. Of Hypo solution
% of Cl₂ = (3.55 × x × V (mL)/W (g))
Where x=Molarity of hypo solution
V =mL of hypo solution used in titration.

Ex.1.   10 gm sample of bleaching powder was dissolved into water to make the solution on liter. To this solution 35 mL of 1.0 M Mohr salt solution was added containing enough H₂SO₄. After the reaction was complete, the excess Mohr salt required 30 mL of 0.1 M KMnO₄ for oxidation. The % of available Cl₂ approximately is (mol wt=71)

Sol.2.  Meq. Of Mohr’s salt =35×1×1=35
Meq. Of KMnO₄=Meq. Of excess Mohr salt=30×0.1×5=15
Meq. Of Mohr salt reacted with bleaching powder =35-15=20
Meq. Of Cl2=20
Wt. of Cl₂ = 20 × 10^-3 × (71/2) = 0.71 gm
% of Cl₂ = (0.71/10) × 100 = 7.1% Ans.

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