Redox and Electrode Potentials

Electrode potentials are given below.

Al³⁺(aq) + 3e^– ⇌ Al(s) –1.676 V

Sn²⁺(aq) + 2e^– ⇌ Sn(s) –0.137 V

A standard cell is constructed from

Al³⁺(aq)|Al(s) and Sn²⁺(aq)|Sn(s) half cells.

Which statement is correct for the standard cell?

• Al is oxidised and the cell potential is 1.539 V.

• Sn is oxidised and the cell potential is 1.539V.

• Al is oxidised and the cell potential is 1.813 V.

• Sn is oxidised and the cell potential is 1.813 V

A cell is constructed from the two redox systems below.

Cu²⁺(aq) + 2e⁻ ⇌ Cu(s) E ө = +0.34 V

Ag+(aq) + e⁻ ⇌ Ag(s) E ө = +0.80 V

Which statement(s) is/are correct for the cell?

1- The cell potential is 1.14 V.

2- The reaction at the copper electrode is Cu(s) → Cu2⁺(aq) + 2e⁻.

3- The silver electrode increases in mass.

• 1, 2 and 3

• Only 1 and 2

• Only 2 and 3

• Only 1

The redox equilibria for a hydrogen–oxygen fuel cell in alkaline solution are shown below. 

2H2O(l) + 2e− ⇌ H2(g) + 2OH−(aq)Ee = −0.83 V 

½O2(g) + H2O(l) + 2e− ⇌ 2OH−(aq)E2 = +0.40 V

What is the equation for the overall cell reaction?

• H2(g) + 4OH−(aq) → 3H2O(l) + ½O2(g)

• 3H2O(l) + ½O2 → H2(g) + 4OH−(aq)

• H2O(l) → H2(g) + ½O2(g)

• H2(g) + ½O2(g) → H2O(l)

Which enthalpy change(s) is/are endothermic?

1- The bond enthalpy of the C–H bond

2- The second electron affinity of oxygen

3- The standard enthalpy change of formation of magnesium

• 1, 2 and 3

• Only 1 and 2

• Only 2 and 3

• Only 1

Four redox systems relevant to hydrogen–oxygen fuel cells are shown below.

H₂O(l) + e– ⇌ OH^–(aq) + ½H₂(g) –0.83

H⁺(aq) + e– ⇌ ½H₂(g) 0.00

½O₂(g) + H₂O(l) + 2e^– ⇌ 2OH^–(aq) +0.40

½O₂(g) + 2H⁺(aq) + 2e^– ⇌ H₂O(l) +1.23

Which statement(s) is/are correct for an alkaline hydrogen–oxygen fuel cell?

1- The reaction at the positive electrode is: ½O2(g) + 2H+(aq) + 2e– → H2O(l)

2- The overall cell reaction is: H2(g) + ½O2(g) → H2O(l).

3- The cell potential is 1.23 V.

• 1, 2 and 3

• Only 1 and 2

• Only 2 and 3

• Only 1