Bleaching Powder

Bleaching Powder

Bleaching powder is calcium chlorohypochlorite.

Preparation

(i) By passing Cl2 gas on slaked lime

Ca(OH)2 + Cl2 → 2 + H2O

Bleaching powder

Properties

(i) White powdered substance having little yellow ting, with smell of chlorine.

(ii) With acids (HCl, dil. H2SO4 etc) chlorine gas is evolved. Total amount of Cl2 gas evolved is known as available chlorine; (generally approx 35%)

CaOCl2 + 2HCl → CaCl 2 + H2O + Cl2

chlorine

Available chlorine is usually determined by Bunsen method and for this acetic acid is added to bleaching powder which liberates all chlorine.

CaOCl2 + 2CH3COOH →  Ca(CH3COO)2 + H2O + Cl2

chlorine

Now, KI solution is added in excess the available chlorine from bleaching powder liberates equivalent amount of Iodine from KI.

2KI + Cl2 →  2KCl + I2

Iodine thus liberated forms brown colour complex with excess of KI

KI + I2 →  KI3 [ KI.. I2]

Iodine bonded with KI is titrated against hypo (sodium thiosulphate) till brown colour disappears.

I2+ 2Na2S2O3 →  2NaI + Na2S4O6

Sodium Sodium

Iodide tetrathionate

(iii) With H2O (moisture) and CO2, Cl2 gas is liberated

CaOCl2+ H2O →  Ca(OH)2 + Cl2

CaOCl2+ CO2 →  CaCO3 + Cl2

(iv) In presence of COCl2(acts as catalyst) gives off O2

2CaOCl2 2CaCl2 + O2

(v) When heated with alcohol and acetone, chloroform is obtained which acts as anesthetic agent

CaOCl2 + H2O →  Ca(OH)2 + Cl2

CH3CH2OH + Cl2  → CH3CHO + 2HCl

CH3CHO + 3Cl2 →  CCl3.CHO + 3HCl

2C.Cl3CHO + Ca(OH)2 →  2CHCl3 + Ca(HCOO)2

chloroform