Page 90 - A Working Method Approach For Introductory Physical Chemistry Calculations

74 Chapter 6
travel via the external circuit to the cathode. At the cathode, the
Cu2+(aq) ions combine with the 2e, producing more copper metal.
This means that at the anode the zinc becomes corroded, and
gradually is eaten away, whereas at the cathode copper metal is
deposited. Since electrons travel from the anode to the cathode (an
easy way to remember this is the two vowels, anode -+ electrons), this
implies that electric current, Z (conventional direction of flow), must
travel in the opposite direction. Since oxidation occurs at the anode
(‘CROA’), i.e. a loss of electrons (‘OILRIG’: oxidation-loss of
ions are produced,
electrons; reduction-gain of electrons), Zn2 +
and so NO3- anions, which are negatively charged, will migrate from
the salt bridge towards the anode, to compensate this generation of
positive Zn2 + (as> cations. Likewise, K+ cations will travel across the
salt bridge towards the cathode.

The Electrochemical Series or the Activity Series
An important application of standard electrode potentials is in
ranking substances according to their reducing and oxidising powers.
The electrochemical or activity series is summarised in Table 6.2.

Table 6.2 The Electrochemical or Activity Series
Scale E”IV Reduction
- 3.00
-3.09 Li+ + e+Li
- 2.93 K+ +e+K
-2.71 Na+ + e+Na
-2.36 M$+ + 2e+Mg
- 2.00
- 1.66 A13+ + 3e-tAl
-1.18 Mn2+ + 2e-tMn
- 1.00
-0.76 Zn2+ + 2e-t~n
-0.44 Fe2+ + 2e + Fe
0.00 0.00 2H+ +2e -+HZ
+ 0.34 cu2+ + 2e+ cu
+ 0.80 Ag+ + e+Ag
+ 1.00
+ 1.69 Au+ + e -+ Au

There is a simple way of memorising this series, which must be known
(it is not necessary to remember the numerical values, these will be