1. Electrochemistry
Exercise

2. Electrochemistry
Question 1
I– must be oxidised to I2
H2O2 must be reduced to H2O B
Eºcell = 1.77 – 0.54 = 1.23 V feasible
Observations:
brown solution; no effervescence.

3. Electrochemistry
Question 2
Eºcell = Eºred – Eºox = 1.2 V
C
• Look at which pair will give a cell E of
1.2 V.
• Bear in mind that the more positive/
less negative redox pair must be
reduced.

4. Electrochemistry
Question 3
2H+ + e– H2 Eº = 0.0 V
B
• For metal not to be dissolved, the
metal ion must be preferentially
reduced i.e. Eº = +
• Cheat: Write out all the Eº; look for
odd one out.

5. Electrochemistry
Question 4
• More +/ Less – Reduced
• More –/ Less + Oxidised C

6. Electrochemistry
Question 5
Strategy: Look for options that indicate
conditions are not standard B and D
D
Eºcell = +1.23 – (– 2.38) = 3.61 V
Use LCP to predict Eºcell under non-
standard conditions:
B [Mg2+]↓ Eºcell will be higher
D [H+]↓ Eºcell will be lower

7. Electrochemistry
Question 6
Strategy:
• Magnesium is a reactive metal; can
only be extracted by electrolysis of
B
molten salt
• MgO: high melting point not feasible
to achieve molten state

8. Electrochemistry
Question 7
Strategy: Write reaction equation
Anode: 2Cl– Cl2 + 2e– A
Cathode: 2H2O + 2e– H2 + 2OH–
Reaction: 2Cl– + 2H2O Cl2 + H2 + 2OH–
n(NaCl) = 58.5 / 58.5 = 1mol
Cl2 H2 NaOH
n/ mol 0.5 0.5 1
m/ kg 35.5 1 40

9. Electrochemistry
Question 8
[×] Pb(SO4)2 will not exist.
B

10. Electrochemistry
Question 9
Strategy:
Look at the oxidation states of the metals. D
1. Fe (III) cannot be oxidised
2. Cr (II) can be oxidised to Fe(III)
3. Fe (II) can be oxidised to Fe(III)

11. Electrochemistry
Question 10
[×] O.S. of N changes from +5 to +1.
B

12. Electrochemistry
Question 11 (iii)
Standard electrode (redox) potential, Eº, of a half-cell is
the potential difference between the electrode potentials of
the half-cell and that of the standard hydrogen electrode,
measured under standard conditions.

13. Electrochemistry
Question 11 (iii)
Strategy:
1. Write down species given.
(I) M Cu2+
(II) M H+
2. Write down possible reactions:
(I) M M2+ Cu2+ Cu
(II) M M2+ H+ H2
3. Check that Eºcell > 0V.

14. Electrochemistry
Mixture of Fe3+,
Question 12 Mn2+, MnO4–
Mixture of Fe2+,
Fe3+, Mn2+ Mixture of
Fe3+ & Mn2+
Only Fe2+
present

15. Electrochemistry
Question 13
1. Identify all ions in solution (including H2O)
2. Cations attracted to cathode;
Anions attracted to anode
3. Find electrode potentials for these half equations
E°
Cathode more positive or less negative is discharged
Anode more negative or less positive is discharged