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) → Cr₂O₇^2-(aq)  + 7H₂O(l)

Cr₂O₇^2- (aq) + 2H⁺ (aq) + 4H₂O₂ (aq) → 2CrO(O₂)₂ (aq) + 5H₂O (l)

Please Subscribe to promote this website. Subscription is free

Share with a friend

Thank you so much