Question

In experiment 7, when concentrated ammonia is added to acidic copper solution, the pale-blue precipitate forms, followed by formation of bright blue soluble compound. Write formulas of the precipitate and of colored complex.

When potassium iodide is added to copper(II) nitrate solution, a brown precipitate forms. Write and balance the corresponding reaction equation.

This brown precipitate is titrated with sodium thiosulfate solution. Write and balance the corresponding equation.

After titration, a white precipitate is left in the solution. Write the formula of this precipitate.

These are not different questions, they all are about the same experiment and branch off one another, if you could answer them all.

Answer 1

when concentrated ammonia is added to acidic copper solution, the pale-blue precipitate forms, followed by formation of bright blue soluble compound. Write formulas of the precipitate and of colored complex.

pale-blue precipitate is Cu(OH)2.

Cu^2+ (aq) + 2 NH3 (aq) + 4 H2O (l).................> Cu(OH)2 (s) + 2 NH4OH (aq) + 2 H+

[Cu(H2O)6]^2+ + 4 NH3 ................> [Cu(NH3)4(H2O)2]^2+ + 4 H2O

bright blue soluble compound is [Cu(NH3)4(H2O)2]^2+.

When potassium iodide is added to copper(II) nitrate solution, a brown precipitate forms. Write and balance the corresponding reaction equation.

2 Cu(NO3)2 (aq) + 4 KI (aq)........................> 2 CuI (s) + I₂ (s) + 2 KNO3 (aq)

brown precipitate is I₂.

This brown precipitate is titrated with sodium thiosulfate solution. Write and balance the corresponding equation.

I₂ (s) + 2 S2O₃^2- (aq)...................> 2 I^- (aq) + S₂O₆^2- (aq)

After titration, a white precipitate is left in the solution. Write the formula of this precipitate.

formula of this precipitate is CuI