Reaction of Cr3+
Its colour is green. A solution of Cr3+ is commonly provided in form of CrCl3(aq). In that case the solution is blue-violet rather than green this is caused by the environment of Cl– and hydrolysis
| Test | Observations | Notes |
|---|---|---|
| Add NH3 | an immediate green ppt soluble in xs is formed | Cr(OH)3(s) |
| Add solid sodium carbonate | Effervescence, gas which tunrs limewater milky is produced.Solution turns to grey-green. A pake green ppt is also formed | Solution of Cr3+(aq) is acidic and so reacts witha carbonate to produce CO. Green ppt is Cr(OH)3(s) |
| Add NaOH(sq) | an immediate grey-green ppt is formed whichis soluble in xs NaOH to form a dark green solution | Grey-green ppt is Cr(OH)3(s). The ppt reacts with further xs OH– ions in a ligand exchange reaction forming a dark green complex [Cr(OH)6]3+ |
| Add NaOH(aq) followed by 20Vol Hydrogen peroxide. | Solution truns yellow | Cr3+ oxidized to CrO42- |