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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