What initially forms as pale blue and pale green precipitates when NH3(aq) is added to [Cu(H2O)6]^2+ and [Ni(H2O)6]^2+ solutions, respectively?
When NH3(aq) is added to [Cu(H2O)6]^2+ and [Ni(H2O)6]^2+ solutions, two different precipitates are formed.
1. [Cu(H2O)6]^2+ solution: When ammonia (NH3) is added to [Cu(H2O)6]^2+ solution, the copper ion (Cu^2+) reacts with the ammonia to form a complex ion called [Cu(NH3)4(H2O)2]^2+. This complex ion is a pale blue precipitate. So, when NH3(aq) is added to [Cu(H2O)6]^2+ solution, a pale blue precipitate forms.
Reaction equation:
[Cu(H2O)6]^2+ + 4NH3 → [Cu(NH3)4(H2O)2]^2+ + 4H2O
2. [Ni(H2O)6]^2+ solution: When ammonia (NH3) is added to [Ni(H2O)6]^2+ solution, the nickel ion (Ni^2+) reacts with the ammonia to form a complex ion called [Ni(NH3)6]^2+. This complex ion is a pale green precipitate. So, when NH3(aq) is added to [Ni(H2O)6]^2+ solution, a pale green precipitate forms.
Reaction equation:
[Ni(H2O)6]^2+ + 6NH3 → [Ni(NH3)6]^2+ + 6H2O
To summarize, NH3(aq) forms a pale blue precipitate ([Cu(NH3)4(H2O)2]^2+) in [Cu(H2O)6]^2+ solution and a pale green precipitate ([Ni(NH3)6]^2+) in [Ni(H2O)6]^2+ solution.
To determine what initially forms as pale blue and pale green precipitates when NH3(aq) is added to [Cu(H2O)6]^2+ and [Ni(H2O)6]^2+ solutions, we need to understand the complex ions formed by the copper and nickel ions with water and ammonia.
When copper(II) ion, Cu2+, is combined with water, [Cu(H2O)6]^2+ complex ion is formed. This complex ion has an octahedral geometry, with six water molecules surrounding a central copper ion.
When ammonia, NH3(aq), is added to the [Cu(H2O)6]^2+ solution, it acts as a ligand, replacing some of the water molecules attached to the copper ion. This forms [Cu(NH3)x(H2O)(6-x)]^2+ complex ions.
The resulting complex ion formed with ammonia is usually pale blue and is called the tetraamminecopper(II) ion, [Cu(NH3)4(H2O)2]^2+. The presence of this complex ion in solution gives the solution a pale blue color.
Now, let's focus on the nickel complex. When nickel(II) ion, Ni2+, is combined with water, [Ni(H2O)6]^2+ complex ion is formed, similar to the copper complex.
When ammonia is added to the [Ni(H2O)6]^2+ solution, it also acts as a ligand, replacing some of the water molecules attached to the nickel ion. This forms [Ni(NH3)x(H2O)(6-x)]^2+ complex ions.
In this case, the resulting complex ion formed with ammonia is usually pale green and is called the hexaamminenickel(II) ion, [Ni(NH3)6]^2+. The presence of this complex ion in solution gives the solution a pale green color.
So, to answer your question, when NH3(aq) is added to the [Cu(H2O)6]^2+ solution, a pale blue precipitate of [Cu(NH3)4(H2O)2]^2+ complex ions initially forms. When NH3(aq) is added to the [Ni(H2O)6]^2+ solution, a pale green precipitate of [Ni(NH3)6]^2+ complex ions initially forms.
Cu^2+ + 4NH3 ==> Cu(NH3)4^2+ blue. May be pale blue in very dilute solutions but more often is a deep blue color.
Ni^2+ behaves similarly but not the same color.