Page 112 - [B._MURPHY,_C._MURPHY,_B._HATHAWAY]_A_working_meth

96 Chapter 7
a knowledge of the relative position of each species within the
Electrochemical Series, as shown in Table 6.2 of Chapter 6.
6. Having established the exact reduced species and the exact
oxidised species at the electrodes, write down the cathode and
anode half-reactions, remembering (as for galvanic cells) that
reduction takes place at the cathode, and that oxidation takes
place at the anode, i.e. 'CROA' and 'OILRIG'.
7. Balance the two half-reactions, so that the number of electrons
transferred is the same for both, and from these reactions,
determine the net cell reaction
8. Draw the electrolytic cell (Figure 7.3).
Label clearly: (a) the anode (LHE) and the cathode (RHE); (b)
the direction of current, I; (c) The direction of electrons; (d) the
direction of ion flow, as derived from the half-cell reactions in
step 6.
9. Re-read the question, to see exactly what you are asked to
determine.
10. Apply Faraday's Second Law of Electrolysis:
Mn+ + ne+M*
=+ nF --+ 1 mol of M
1F -+ l/n mol of M
96 500 C --+ l/n moles of M

where Q = charge (measured in coulombs, C), I = current
(measured in amperes, A); t = time (measured in seconds, s).
11. Answer any riders to the question:
(a) Standard state conditions: most stable state at 25 "C (298 K)
and 1 bar pressure.
(b) 1 mol of an ideal gas at 25 "C (298 K) and 1 bar pressure
occupies 24.8 dm3.

Remembered by 'Peas and Vegetables go on the Table!'
(d) pH = -loglo[H,O+]; pOH = -l~glo[OH-]; pH + pOH = 14