Answer to Question #211743 in Physical Chemistry for Reese

Question

The electrodes in the following electrochemical cell are connected to a voltmeter as shown. The half-cell on the right contains a standard silver-silver chloride electrode (a silver wire coated with AgCl(s), as in questions 5 and 6).  

AgCl (s) + e^- → Ag(s) + Cl^- (1 M)      E° = 0.2223 V

The half-cell on the left contains a silver electrode immersed in 100.0 mL of 1.00 x 10^-3 M AgNO₃(aq). A porous plug through which ions can migrate separates the half-cells. 

What is the voltmeter reading after 10.00 mL of 0.0100 M K₂CrO₄ has been added to the half-cell on the left and the mixture has been thoroughly stirred? 

Hint: K_sp of Ag₂CrO₄ = 1.1 x 10^-12

Answer 1

Ag/AgCl electrode is insoluble salt type electrode, here redox reaction of Ag takes place as

AgCl(s) + e– → Ag(s) + Cl–(aq). (1)

Also Ag falls below H in electrochemical series (+0.8 V vs SHE) and hence can behave as non- polarizable electrode i.e. its potential doesn't change by passing current through it so this type of electrodes can be used as reference electrodes. half cell reaction for this electrode can be written as

... || Cl– (aq) | AgCl (s) | Ag (s)  (2)

so just like any other secondary reference electrode one can use this electrode. the other electrode in this case could be any electrode system under investigation. 

the Ecell of the system under investigation can be found out 

Ecell = Eindicator −Ereference (3)

so if we compare this equation to standard equation

Ecell = Ecathode −Eanode (4)

and rearrange the (4) to

Eindicator = Ecell + Ereference (5) i.e. Ecathode = Ecell + Eanode (6)