The anode in the above cell can actually be considered a standard hydrogen electrode if concentrations were standardized. That would make the cathode an ion selective electrode. What analyte would the electrode be detecting? And what component of the cathode would you replace by the solution containing the unknown concentrations of analyte?

  

Pt (s)1 | H2 (g, 1.00 bar) | HCI (5.00E-4 M) || KCI(0.100 M) | Hg) | Hg2Cl2{s)