Qualitative analysis of chromium (III) salts
Qualitative analysis of chromium (III) salts
With sodium hydroxide solution:
It forms a green precipitate soluble in excess
Cr3+ (aq) + 3OH– (aq) → Cr(OH)3 (s)
Cr(OH)3(s) + OH–(aq) → Cr(OH)4– (aq)
With dilute ammonia solution:
It forms a green precipitate insoluble in excess
Cr3+ (aq) + 3OH– (aq) → Cr(OH)3 (s)
Confirmatory test;
It forms a green precipitate with sodium hydroxide soluble in excess turns yellow with hydrogen peroxide solution and temporary blue when a few drops of concentrated sulphuric acid are added to the mixture..
Equations
Cr3+ (aq) + 3OH– (aq) → Cr(OH)3 (s)
Cr(OH)3(s) + OH–(aq) → Cr(OH)4– (aq
2Cr(OH)4– (aq) + 3H2O2 (aq) → Cr2O72-(aq) + 7H2O(l)
Cr2O72- (aq) + 2H+ (aq) + 4H2O2 (aq) → 2CrO(O2)2 (aq) + 5H2O (l)
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