Electrochemical

Reactions

4

4.1 Introduction

ESCBH

Reaction Types in Grade 11 discussed oxidation, reduction and redox reactions. Oxi-

dation involves a loss of electrons and reduction involves a gain of electrons. A redox

reaction is a reaction where bothoxidation and reductiontake place. What is common

to all of these processesis that they involve a transfer of electrons and a change in the

oxidation state of the elements that are involved.

See introductory video:VPmxy at http://www.everythingscience.co.za

Exercise 4 - 1

1. Define the terms oxidation and reduction.


2. In each of the following reactions say whether the iron in the reactants is oxidised
   or reduced.

(a) Fe→ Fe2++ 2e−

(b) Fe3++ e−→ Fe2+

(c) Fe 2 O 3 + 3CO→ 2Fe + 3CO 2

(d) Fe2+→ Fe3++ e−

(e) Fe 2 O 3 + 2Al→ Al 2 O 3 + 2Fe

3. In each of the following equations, say which elements in the reactants are oxi-
   dised and which are reduced.

(a) CuO(s) + H 2 (g)→ Cu(s) + H 2 O(g)

(b) 2NO(g) + 2CO(g)→ N 2 (g) + 2CO 2 (g)

(c) Mg(s) + FeSO 4 (aq)→ MgSO 4 (aq) + Fe(s)

(d) Zn(s) + 2AgNO 3 (aq)→ 2Ag + Zn(NO 3 ) 2 (aq)

4. Which one of the substances listed below acts as the oxidising agent in the fol-
   lowing reaction?

3SO 2 + Cr 2 O^27 −+ 2H+→ 3SO^24 −+ 2Cr3++ H 2 O

(a) H+

(b) Cr3+