Page 97 - [B._MURPHY,_C._MURPHY,_B._HATHAWAY]_A_working_meth

Electrochemistry I: Galvanic Cells 81

Solution:
1. There is no mention of 'electrolysis' or 'electrolysed'; therefore
the cell in question is a galvanic cell.
2- pt(s)IH2(g)I~
+(as) II Cl-(aq)IAgCl(s)IA&s)
(a) LHE is a gas-ion electrode, namely the standard hydrogen
electrode (SHE).
(b) RHE is a metal-insoluble salt anion electrode.
3. No balanced chemical equation is given. Hence, the E" values
can be used to determine which electrode is acting as the cathode:
Eo(Ag(s)lAgCl(s)lCl-(aq)) = +0.222 V; EO (~+(aq)(~2(g)) =
0.000 V (the SHE; value not given but should be known).
Therefore Ag(s)lAgCl(s)JCl-(aq) acts as the cathode as this is the
more positive E" value, and the SHE is the anode.
4. One-line representation of the cell:
Pt(s)IH2(g)I~+(aq)IIC1-(*q)IAgC1(s)IAg(s)
5. Anode reaction (SHE): H2(g) (0); H+(a (I).
9
Hence, 0 -1 (oxidation), i.e. H2(g) + H (aq) + e oxidation
Therefore, H2(!) -+ 2H+(,) + 2e or iH2(g) -, H+(,q) + e
Cathode reaction: Ag(,) (0); Cl-(,,) (-1); AgCl(s): Ag (I);
c1 (-1).
There is no change in the oxidation state of the chlorine
(-1 -, -I), but there is a change in the oxidation state of the
silver (I -+ 0).

6 Anode reaction: iH2(g) -, Hf(,) + e
Cathode reaction: AgCl,,) + e -+ Ago) + Cl-(aq)

7. Diagram of the cell (Figure 6.9)
8. E"=ll = E"RHE - EOLHE = (+ 0.222) - (0.000) V = + 0.222 V.