[lalex0710]

Here's a question that took me a long time and I still couldn't fully figure it out.

An electrolytic cell is set up with an electrolyte H2Se(aq). The  nickel electrodes are weighed before and after the experiment. A voltage supply is set for 0.70 V. The cell is connected. List the primary and secondary equations.

[Borek]

You have to show your attempts at solving the question to receive help. This is a forum policy.

What can happen with Ni?

What is H₂Se? Hint: think about its lighter cousin without an 'e'.

[lalex0710]

I know that Nickel has to be the anode since it is stated to be the electrode, and must be the one undergoing oxidation. 
Ni ---> Ni2+ + 2e- But I couldn't quite figure out which is the cathode of the reaction. I'm also assuming there is a primary and secondary equation since there are three species present, but I don't know which is the primary and which is secondary. So, h2se can also be a cathode right? Then is h2o or is h2se a cathode, or can there be two reactions at the cathode and also the other way around. much help would be appreciated. thanks

[Borek]

You have also water which can react on electrodes.

Think what will happen with Ni²⁺ in the solution...