[ldixon]

I had to find 5 unknown solutions in a recent chem lab and now I am doing the equations, but im not sure about two of them:

Deep blue percipitate
NH3 (aq) + CuSO4 (aq) -------> Cu(NH3)4 SO4 (s)

brown heavy percipitate
4NaI (aq) + 2CuSO4 (aq) -------> 2CuI (s) + I2 (s) + 2Na2SO4 (aq)

Are these reactions correct?  I got percipitates for both of them.

[ldixon]

can anyone help me with this one? 

[Borek]

First is wrong. Cu(NH₃)₄²⁺ is what is produced when your precipitate dissolves in excess ammonia.

[AWK]

I had to find 5 unknown solutions in a recent chem lab and now I am doing the equations, but im not sure about two of them:

Deep blue percipitate
NH3 (aq) + CuSO4 (aq) -------> Cu(NH3)4 SO4 (s)

brown heavy percipitate
4NaI (aq) + 2CuSO4 (aq) -------> 2CuI (s) + I2 (s) + 2Na2SO4 (aq)

Are these reactions correct?  I got percipitates for both of them.

Stoichiometry of reaction is correct. In the first case you got a deep blue solution. In the second case - iodine forms a brown precipitate, CuI is almost white.

[ldixon]

Borek would the first one just be:

NH3 (aq) + CuSO4 (aq) -------> Cu(NH3)2 (aq) + SO4 (aq)

Is the second one correct?

[Borek]

Write correct charges. 4 not 2 ammonia molecules.

[ldixon]

So it would be:
4NH3(aq) + CuSO4(aq) --------> Cu(NH3)4(aq) + SO4(aq)

Would this be a percipitate? 

[Borek]

Charges are still wrong. Besides, CuSO4 was dissociated from the start, SO₄^2- is just a spectator.

[ldixon]

Ok by charges you mean?
                                                           
4NH3^-1(aq) + Cu⁺²SO4^-2(aq) --------> Cu⁺⁴(NH3^-1)4(aq) + SO4^-2(aq)

Yes I understand that SO₄^2- is a spectator but im not sure if this is a percipitate?

Or since SO4^-2(aq) is a spectator it would just be:
4NH3^-1(aq) + Cu⁺²(aq) --------> Cu⁺⁴(NH3^-1)4(aq)

[Dan]

Ammonia, (NH₃) is neutral, and Cu⁺⁴ is wrong

remember, charges must balance

[Borek]

Precipitate is copper hydroxide, it gets dissolved when you add more ammonia. CuSO₄ is well soluble. Sulfates of copper/ammonia complexes are well soluble as well.

[ldixon]

Is there a way to write an equation for this whole reaction?

If the charge on (NH3) is neutral then Cu would also be neutral?

[Borek]

No, copper cation has a charge, as well as sulfate anion. Note: copper sulfate molecule is neutral, so the copper cation must have charge opposite to sulfate.