3S + 7H O + (iv) It oxidises sulphur dioxide to sulphate ion Cr O + 3SO + 2H 2Cr + 3SO + H O + (v) It oxidises stannous salts to stannic salt Cr O + 3Sn + 14H 2Cr + 3Sn + 7H O + (vi) It oxidises alcohols to acids. 2K Cr O + 8H SO + CH CH OH 2K SO + 2Cr SO + 3C H COOH + 11H O . Chromyl chloride test: When potassium dichromate is heated with any chloride salt in the presence of Conc H SO , orange red vapours of chromyl chloride (CrO Cl ) is evolved. This reaction is used to confirm the presence of chloride ion in inorganic qualitative analysis.
K Cr O + 4NaCl + H SO 2KHSO + 4NaHSO + 2CrO Cl C hromyl chloride + 3H O ↑ The chromyl chloride vapours are dissolved in sodium hydroxide solution and then acidified with acetic acid and treated with lead acetate. A yellow precipitate of lead chromate is obtained. CrO Cl + 4NaOH Na CrO + 2NaCl + 2H O Na CrO + CH COO Pb PbCrO + 2C ↓ Leadchromate Yellowprecipitate H COONa Uses of potassium dichromate: Some important uses of potassium dichromate are listed below. .
It is used as a strong oxidizing agent. . It is used in dyeing and printing. .
It used in leather tanneries for chrome tanning. . It is used in quantitative analysis for the estimation of iron compounds and iodides. XII U4-D-Block-Jerald XII U4-D-Block-Jerald - - - - Potassium permanganate - KMnO Preparation: Potassium permanganate is prepared from pyrolusite (MnO ) ore.
The preparation involves the following steps. (i) Conversion of MnO to potassium manganate: Powdered ore is fused with KOH in the presence of air or oxidising agents like KNO or KClO . A green coloured potassium manganate is formed. 2MnO + 4KOH + O K MnO potassium manganate Green 2H O (ii) Oxidation of potassium manganate to potassium