CHAPTER 4. ELECTROCHEMICAL REACTIONS 4.4
(d) Cr 2 O^27 −(IEB Paper 2, 2004)- If zinc is added to asolution of magnesiumsulphate, will the zinc displace the
magnesium from the solution? Give a detailed explanation for your answer.
More practice video solutions or help at http://www.everythingscience.co.za(1.) 01qq (2.) 01qr (3.) 01qs (4.) 01qt (5.) 01qu (6.) 01qv
(7.) 01qwCombining half cells ESCBX
Using the example of the zinc and copper halfcells, if we combine these cells as we
did earlier in the chapter (section 4.2), the following two equilibria exist:
Zn2++ 2e−� Zn(E^0 =− 0 .76V)Cu2++ 2e−� Cu(E^0 = +0.34V)We know from demonstrations, and also by looking at the sign of theelectrode po-
tential, that when thesetwo half cells are combined, zinc will be the oxidation half-
reaction and copper will be the reduction half-reaction. A voltmeter connected to this
cell will show that the zinc electrode is more negative than the copper electrode. The
reading on the meter will show the potential difference between the twohalf cells. This
is known as the electromotive force (emf) of the cell.
DEFINITION: Electromotive Force (emf)
The emf of a cell is defined as the maximum potential difference be-
tween two electrodes orhalf cells in a voltaic cell. Emf is the electrical
driving force of the cellreaction. In other words, the higher the emf,
the stronger the reaction.