Electrochemistry

The standard electrode potentials for three half-cells are given below.

X²⁺ / X ; E^ө = – 0.44 V

Y²⁺ / Y ; E^ө = – 0.76 V

Z²⁺ / Z ; E^ө = +0.34 V

Which of the following can reduce Sn²⁺ (aq) to Sn (s) at 298K?

(The standard electrode potential for Sn²⁺ (aq) / Sn (s) at 298 K is 0.14 V)

• X and Y only

• X, Y and Z

• X²⁺ and Y²⁺only

• Y²⁺ and Z only

What is the standard e.m.f. of the cell shown in the following diagram?

(Standard electrode potentials: Fe²⁺ / Fe,– 0.44V; Fe³⁺ / Fe,– 0.04V; Fe³⁺ / Fe²⁺ ,+ 0.77V; Pb²⁺ / Pb,– 0.13V)

• 1.67V

• 0.90V

• 0.64V

• 0.31V

The standard electrode potentials for some half-cell reactions are given below

Half-cell reaction Eө / V

½ Br₂ + e --> Br ^– + 1.07

Fe³⁺ + e --> Fe²⁺ + 0.77

½ I₂ + e --> I ^– + 0.54

Which pairs of species can react with each other based on the above data?

• I ^– and Fe³⁺

• Br₂ and Fe²⁺

• I₂ and Br ^–

The standard reduction electrode potential for several half-reactions at 298K are shown.

Based on the above data, which of the following statements is correct?

• Fe²⁺ is the strongest oxidizing agent.

• H₂O₂ can spontaneously oxidise Fe²⁺ ions.

• The highest e.m.f. is obtained for cells I and III.

• Both Fe³⁺ and Sn²⁺ ions can react with Mn²⁺.

After a steady current of 18.0 A was passed for 20.0 minutes through a solution of copper(II) sulphate, the mass of the impure copper anode decreased by 8.01 g. What is the percentage purity of copper in the impure copper rod? [Ar Cu = 63.5 ; Faraday’s constant = 96500 C mol^-1]

• 73.5%

• 79.6%

• 81.2%

• 88.7%

Which of the following is true about the Danielle cell?

• The e.m.f is 1.5V

• The cathode is negatively charged.

• Electricity flows from the zinc electrode to the copper electrode

  outside the cell.

• The electron flows from anode to cathode outside the cell.

Mg²⁺ + 2e --> Mg; E = - 2.38V

Fe³⁺ + e --> Fe²⁺; E = +0.77V

Calculate the e.m.f. of the following cell:

Mg l Mg²⁺ (10M) ll Fe³⁺ (5M) l Fe²⁺(1m) l Pt

• - 0.86V

• – 2.31V

• + 3.16V

• + 4.17v

During electrolysis of a copper(II) salt solution between copper electrodes, the mass of copper electroplated on the cathode depends on

• The electric current

• The time taken

• The characteristics of anions present

In which of the following pairs of spesies is the sulphur in the same oxidation state in both members of the pairs?

• SF₆ and SO₄^2-

• SO₂ and HSO₃^-

• S₂O₃^2- and S₄O₆^2-

The e.m.f. of the cell Pt(s) |H₂(g)|H⁺(aq)||Ag⁺(aq)|Ag(s) would be increased by

• increasing the concentration of H⁺(aq).

• increasing the surface area of the Pt electrode.

• increasing the concentration of Ag⁺(aq).

• decreasing the pressure of H₂(g).