a galvanic cell: A copper electrode is placed in a Cu(NO3)2 electrolyte. An iron electrode is placed in a Fe(NO3)3 electrolyte.

Question

a) What will happen to the voltage if sodium sulfide solution was added to the copper solution(I found that CuS(solid precipitate) will be formed, but i'm thinking it will reduce the voltage but im not sure)

b) What will happen is Na2S was added to the iron solution

if this helps, here are the half reactions for each half cell

Fe^3+ + e ---> Fe ^2+
Cu^2+ + 2e ---->Cu

Answer 1

Sulfide added to the copper nitrate will ppt CuS.
CuS ==> Cu^+2 S^=
Remember CuS has a Ksp (solubility product) so the E value for that half cell will be changed to reflect the change of Cu concentration from the initial value (not listed in your post) to the new value present in a saturated solution of CuS.

b. Same thing for the iron solution.
Fe^+3 + S^= ==> Fe2S3 and there is a Ksp for Fe2S3