I have made voltaic cell as follows.
Zn(s) | ZnCl(aq) 0.1M || CuCl(aq) 0,1M | Cu(s)
The EMS was measured with a voltmeter at 1,02V.
Then by addition of Na2S, to the cathode side I witnessed some precipitation. I'm reasoning that the precipitation is of ZnS(s)
According to the Nernst equation; since [Zn2+] < [Cu2+] now
Q<1 and therefore the EMS should rise. However, this is not what was observered, rather the measured EMS went down.
How can I find an explaination for this?