Everything Science Grade 12

4.5 CHAPTER 4. ELECTROCHEMICAL REACTIONS

(d)

Pb|Pb2+||Hg2+|Hg

3. Given the followingtwo half-reactions:
   
   
   • Fe3+(aq) + e−� Fe2+(aq)
   
   
   • MnO− 4 (aq) + 8H+(aq) + 5e−� Mn2+(aq) + 4H 2 O(l)
   
   
   
   

(a) Give the standard electrode potential for each half-reaction.

(b) Which reaction takes place at the cathode and which reaction takesplace

at the anode?

(c) Represent the electrochemical cell using standard notation.

(d) Calculate the emf ofthe cell

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(1.) 01r1 (2.) 01r2 (3.) 01r3

4.5 Balancing redox reactions ESCBZ

Half reactions can be used to balance redox reactions. We are goingto use some

worked examples to help explain the method.

Example 7: Balancing redox reactions

QUESTION

Magnesium reduces copper (II) oxide to copper.In the process, magnesium is

oxidised to magnesiumions. Write a balanced equation for this reaction.

SOLUTION

Step 1 : Write down the unbalanced oxidation half reaction.

Mg→ Mg2+