Reactions of metal ions with bases

Ion: Cr3+

Species in aqueous solution: Violet or Green, [Cr(H2O)6]3+

With Sodium Hydroxide solution: Green Precipitate, [Cr(H2O)3(OH)3]

With Excess Sodium Hydroxide solution: Dissolves to give a green solution containing [Cr(OH)6]3-

Ion: Mn2+

Species in aqueous solution: Very Pale Pink, [Mn(H2O)6]2+

With Sodium Hydroxide solution: Off-white Precipitate [Mn(H2O)4(OH)2] Turns brown in air, Oxidised to MnO2

With Excess Sodium Hydroxide solution: Does not dissolve

Ion: Fe2+

Species in aqueous solution: Pale Green [Fe(H2O)6]2+

With Sodium Hydroxide solution: Green Precipitate [Fe(H2O)4(OH)2] Rapidly turns brown in air, oxidised to Fe(OH)3

With Excess Sodium Hydroxide solution: Does not Dissolve

Ion: Fe3+

Species in aqueous solution: Yellow/Brown [Fe(H2O)6]3+

With Sodium Hydroxide solution: Reddish-Brown precipitate [Fe(H2O)3(OH)3]

With Excess Sodium Hydroxide solution: Does not dissolve

Ion: Cu2+

Species in aqueous solution: Blue [Cu(H2O)6]2+

With Sodium Hydroxide solution: Pale blue precipitate [Cu(H2O)4(OH)2]

With Excess Sodium Hydroxide solution: Does not dissolve

Ion: Zn2+

Species in aqueous solution: Colourless [Zn(H2O)6]2+

With Sodium Hydroxide solution: White Precipitate [Zn(H2O)4(OH)2]

With Excess Sodium Hydroxide solution: Dissolves to give a colourless solution containing [Zn(H2O)2(OH)4]2-