[spiderman1441]

1-In Third grpup cations , why Al⁺³ & Zn⁺² are colorless , and why they form a white percipitate , i.e why they don't form colored percipitates ?

2- What,s the reagent of Al ?

[Dan]

1. What is it that gives transition metal compounds their colour? Why might you not see this in Zn(II) and Al(III) compounds?

oh, also Zn is not group III

2. Please rephrase the question, it doesn't make sense.

[Albert]

2- What,s the reagent of Al ?

What reagent is generally used to precipitate aluminium?

Ammonia and ammonium chloride, at pH= 8.5 - 9

[mdlhvn]

1-In Third grpup cations , why Al⁺³ & Zn⁺² are colorless , and why they form a white percipitate , i.e why they don't form colored percipitates ?

1. Why does matter have colours or not? Because they can absorb visible light whose wavelengths range from about 400nm to 800nm.

2. Then why Al³⁺ and Zn²⁺ can not absorb visible light. Remenber that in solution, they exist under hydrate forms, that is Meⁿ⁺(H2O)n and can be considered as  complexes.

   There are some theories explaining the structure of complex including the explanation of their light-absorbed ability.