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Hexaaqua chromium [ Cr(H 2 O) 6 ] 3+

Hexaaqua chromium [ Cr(H 2 O) 6 ] 3+. Acidity of hexaaqua transition metal ions. [Cr(H 2 O) 6 ] 3 + is more acidic than [ Co(H 2 O) 6 ] 2+ and [ Cu(H 2 O) 6 ] 2+

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Hexaaqua chromium [ Cr(H 2 O) 6 ] 3+

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  1. Hexaaquachromium [Cr(H2O)6]3+

  2. Acidity of hexaaqua transition metal ions • [Cr(H2O)6]3+ is more acidic than [Co(H2O)6]2+ and [Cu(H2O)6]2+ • In the Chromium 3+ ions, the electrons in the O-H bonds will be pulled even more towards the metal ion than in 2+ ions like Cobalt 2+ and copper 2+. • That means that the hydrogen atoms in the ligand water molecules will be more readily lost in [Cr(H2O)6]3+ than [Co(H2O)6]2+ and [Cu(H2O)6]2+and so the [Cr(H2O)6]3+ ismore acidic and has a lower pH

  3. Ligand exchange of hexaaqua chromium • [Cr(H2O)6]3+ more readily participates in ligand exchange than the other complex ions ([Co(H2O)6]2+ and [Cu(H2O)6]2+) used in the practical for P7 • In most of the chemical reactions carried out three of the H2O ligands in the [Cr(H2O)6]3+ were replaced while only two of water ligands were replaced in the chemical reactions of [Co(H2O)6]2+ and [Cu(H2O)6]2+

  4. Hexaaqua chromium Reaction with sodium hydroxide Hydroxide ions fromsodium hydroxide solution remove hydrogen ions from the water ligands attached to the chromium ion. Once a hydrogen ion has been removed from three of the water molecules, you are left with a complex with no charge - a neutral complex. This is insoluble in water and a blue precipitate is formed.

  5. Hexaaqua chromium Reaction with ammonia This is complex is insoluble in water and is a blue precipitate

  6. Hexaaqua chromium Reaction with sodium carbonate If you add sodium carbonate solution to a solution of hexaaquachromium(III) ions, you get exactly the same precipitate as if you added sodium hydroxide solution or ammonia solution. you will get either hydrogencarbonate ions formed or carbon dioxide gas from the reaction between the hydrogen ions and carbonate ions.

  7. Hexaaqua chromium Reaction with concentrated HCl [Cr(H2O)4Cl2]+ + 2Cl- [Cr(H2O)4Cl2]+ + 2H2O Two of the water molecules are replaced by chloride ions to give the tetraaquadichlorochromium(III) ion which is a dark green colour

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