Topic 6.2: Electron Transfer Reactions Questions

Using the activity series, predict whether a reaction occurs when a piece of magnesium is placed in zinc sulfate solution, ZnSO₄(aq).

Justify your answer and, if a reaction occurs, write the balanced equation.

Distinguish between a voltaic cell and an electrolytic cell in terms of the type of reaction and the energy conversion involved. [2]

A voltaic cell is set up from a magnesium electrode in Mg²⁺(aq) joined by a salt bridge to a copper electrode in Cu²⁺(aq).

Magnesium is the more reactive metal.

State which electrode is the anode and its sign, and write the half-equation occurring there. [3]

A standard voltaic cell is constructed from a tin half-cell, E°(Sn²⁺/Sn) = −0.14 V, and a silver half-cell, E°(Ag⁺/Ag) = +0.80 V.

(i) Calculate the standard cell potential, E°cell.

(ii) Deduce whether the cell reaction is spontaneous, giving a reason. [3]

Using E°(Fe²⁺/Fe) = −0.44 V and E°(Cu²⁺/Cu) = +0.34 V, identify the oxidising agent and the reducing agent in the spontaneous cell, and write the overall ionic equation for the cell reaction. [3]

Molten magnesium chloride, MgCl₂(l), is electrolysed using inert electrodes.

(i) Write the half-equation at the cathode.

(ii) Write the half-equation at the anode.

(iii) State the product formed at each electrode. [3]

Deduce the oxidation state of chromium in the dichromate ion, Cr₂O₇²⁻.

A student adds copper metal to silver nitrate solution and observes that crystals of silver form and the solution turns blue.

Explain, in terms of oxidation states and electron transfer, why this is a redox reaction.

Aluminium metal reacts with copper(II) ions, Cu²⁺, in solution.

Deduce the oxidation and reduction half-equations, then deduce the overall balanced equation. [3]

You are given the two half-equations below for a methanol fuel cell. Combine them to deduce the balanced overall reaction. [2]

CH₃OH + H₂O → CO₂ + 6H⁺ + 6e⁻
O₂ + 4H⁺ + 4e⁻ → 2H₂O

A current of 4.00 A is passed through molten zinc chloride for 25.0 minutes.

The cathode half-equation is Zn²⁺(l) + 2e⁻ → Zn(l).

Calculate the mass of zinc deposited at the cathode.

(M(Zn) = 65.38 g mol⁻¹.) [4]

When carbon monoxide reduces iron(III) oxide in a blast furnace, Fe₂O₃ + 3CO → 2Fe + 3CO₂.

Explain, by reference to oxidation-state changes, why this is a redox reaction and identify the reducing agent. [3]