Transition metals

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Cobalt 2+

The hexaqua ion is pink which is (Co(H20)6)2+

By adding NaOH or NH3 it is changed into (Co(H20)4(OH)2) ppt

If this is left standing then Co(OH)3 ppt is formed

But if excess NH3 is added instead then (Co(NH3)6)2+ solution is formed. And if this is left standing then (Co(NH3)6)3+ solution is formed (its now 3+ because it has been oxidised and therefore has lost an electron)

If Na2CO3 is added to the hexaqua ion then CoCO3 ppt is formed (its mauve)

The NaOH reaction can be reversed by adding H+/acid

If conc HCl is added to the hexaqua ion then (CoCl4)2- solution is formed. This can be reversed by adding water

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Copper 2+

The hexaqua ion is (Cu(H20)6)2+

If NaOH or NH3 is added (Cu(H20)4(OH)2) ppt is formed

If excess ammonia is added then (Cu(NH3)4(H20)2)2+ solution is formed

If Na2CO3 is added then CuCO3 ppt is formed 

If conc HCl is added then (CuCl4)2- solution is formed (green yellow sol). This can be reversed by adding water


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Iron 2+

The hexaqua ion is (Fe(H20)6)2+

If you add NaOH or NH3 then (Fe(H20)4(OH)2) ppt is formed

If this is left to stand then (Fe(H20)3(OH)3) ppt is formed

If Na2CO3 is added then FeCO3 ppt is formed

If Mn04- or (Cr207)2- is added then (Fe(H20)6)3+ is formed

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Iron 3+

The hexaqua ion is (Fe(H20)6)3+

If NH3, NaOH or Na2CO3 is added then (Fe(H20)3(OH)3) ppt is formed


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Chromium 3+

The hexaqua ion is (Cr(H20)6)3+

This can be oxidised by the air to (Cr(H20)6)2+ solution. This can be reversed by adding Zn/HCl

If NaOH, NH3 or NaCO3 is added to the hexaqua ion then (Cr(H20)3(OH)3) ppt is formed

If excess OH- is added to this (Cr(OH)4(H20)2)2- solution is formed

If excess ammonia is added instead then (Cr(NH3)6)3+ is formed

If H202/OH- is added to the hexaqua ion then (Cr04)2- is formed. This reaction can be reversed by adding Zn/HCl

This can then be changed into (cr207)2- solution by adding H+. This reaction can be reversed by adding OH-.

This can the be converted back into the hexaqua ion by adding Fe3+


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Aluminium 3+

The hexaqua ion is (Al(H20)6)3+ (its colourless)

If NH3, NaOH or Na2CO3 is added then (Al(H20)3(OH)3 ppt (white ppt) is formed

 (Al(OH)4)- (a white ppt) is formed if excess OH- is added 

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