Mr Cole Chemistry

Commercial Cells Questions

Commercial Cells

Batteries & Fuel Cells

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Useful Half-Equations

Half-Equation	E^o (V)
MnO₂(s) + H₂O(l) + e⁻ → MnO(OH)(s) + OH⁻(aq)	+0.74 V
Li⁺ + CoO₂ + e⁻ → LiCoO₂	+0.60 V
NiO(OH)(s) + H₂O(l) + e⁻ → Ni(OH)₂(s) + OH⁻(aq)	+0.52 V
Ag₂O(s) + H₂O(l) + 2e⁻ → 2Ag(s) + 2OH⁻(aq)	+0.34 V
Li⁺ + MnO₂ + e⁻ → LiMnO₂	-0.15 V
Zn²⁺(aq) + 2e⁻ → Zn(s)	-0.76 V
[Zn(NH₃)₂]²⁺ + 2e⁻ → Zn + 2NH₃	-0.80 V
Cd(OH)₂(s) + 2e⁻ → Cd(s) + 2OH⁻(aq)	-0.88 V
ZnO(s) + H₂O(l) + 2e⁻ → Zn(s) + 2OH⁻(aq)	-1.26 V
Li⁺ + e⁻ → Li	-3.04 V

1. An alkaline AAA battery is made using a zinc half-cell and a Manganese oxide half-cell.

a) Write the ionic equation for the reaction.

2MnO₂(s) + H₂O(l) + Zn(s) → 2MnO(OH)(s) + ZnO(s)

(Derived from: Cathode: 2MnO₂ + 2H₂O + 2e⁻ → 2MnO(OH) + 2OH⁻ and Anode: Zn + 2OH⁻ → ZnO + H₂O + 2e⁻).

b) Calculate the EMF of the cell.

EMF = E(cathode) – E(anode)
= +0.74 – (-1.26) = 2.00 V

c) State which half-cell is the anode and which is the cathode.

Cathode (Reduction): Manganese oxide half-cell.
Anode (Oxidation): Zinc half-cell.

2. A lithium-ion battery is made using a LiCoO₂ half-cell and a Li⁺/Li half-cell.

a) Calculate the EMF of the cell.

+0.60 – (-3.04) = 3.64 V

b) State the oxidation number of Cobalt in LiCoO₂.

+3
(Li = +1, O = -2 x 2 = -4. Total charge is 0, so Co must be +3).

c) Write the equation for the reaction that occurs when the battery is discharging.

CoO₂ + Li→LiCoO₂

d) Write the equation for the reaction that occurs when the battery is charging.

LiCoO₂→CoO₂ + Li

e) Lithium battery powered cars are often seen as a green alternative to internal combustion engine cars. Explain why.

The electricity used to charge them can be produced from renewable sources (like wind or solar) that do not release carbon dioxide, unlike burning petrol/diesel.

3. A different lithium-ion battery is made of a Li⁺/Li half-cell and a LiMnO₂ half-cell.

a) Calculate the EMF of the cell.

-0.15 – (-3.04) = 2.89 V

b) Write the notation for the cell.

Full Notation: Li(s) | Li⁺(aq) || Li⁺(aq), MnO₂(s), LiMnO₂(s) | Pt(s)

Simplified: Li | Li⁺ || Li⁺, MnO₂, LiMnO₂ | Pt

(Note: An inert electrode like Pt or Graphite is required on the right because the reaction involves solids and ions, but no conductive metal is produced/consumed).

c) Write the equation for the reaction that occurs when the battery is discharging.

MnO₂ + Li→LiMnO₂

d) Write the equation for the reaction that occurs when the battery is charging.

LiMnO₂→MnO₂ + Li

4. A nickel cadmium battery is made from a NiO(OH) half-cell and a Cd(OH)₂ half-cell.

a) State the oxidation state of the nickel in NiO(OH).

(OH is -1, O is -2. Ni + (-2) + (-1) = 0, so Ni = +3).

b) Calculate the EMF of the cell.

+0.52 – (-0.88) = 1.40 V

c) Write an equation for the reaction that occurs when the cell is discharging.

2NiO(OH) + 2H₂O + Cd→2Ni(OH)₂ + Cd(OH)₂