DP Chemistry Questionbank

The Geobacter species of bacteria can be used in microbial fuel cells to oxidise aqueous ethanoate ions,
CH₃COO⁻(aq), to carbon dioxide gas.

State the half-equations for the reactions at both electrodes.

A concentration cell is an example of an electrochemical cell.

(i) State the difference between a concentration cell and a standard voltaic cell.

(ii) The overall redox equation and the standard cell potential for a voltaic cell are:

Zn (s) + Cu²⁺ (aq) → Zn²⁺ (aq) + Cu (s)     E^θ_cell = +1.10 V

Determine the cell potential E at 298 K to three significant figures given the following concentrations in mol dm⁻³:

[Zn²⁺] = 1.00 × 10⁻⁴       [Cu²⁺] = 1.00 × 10⁻¹

Use sections 1 and 2 of the data booklet.

(iii) Deduce, giving your reason, whether the reaction in (b) (ii) is more or less spontaneous than in the standard cell.

Suggest a way in which they are similar.

Outline the difference between primary and rechargeable cells.

Deduce half-equations for the reactions at the two electrodes and hence the equation for the overall reaction.

Identify one factor that affects the voltage of a cell and a different factor that affects the current it can deliver.

Explain how the flow of ions allows for the operation of the fuel cell.

Deduce the half-cell equations occurring at each electrode during discharge.

Outline the function of the proton-exchange membrane (PEM) in the fuel cell.

Outline one advantage and one disadvantage of the methanol cell (DMFC) compared with a hydrogen-oxygen fuel cell.

Deduce the half-equations and the overall equation for the reactions taking place in a direct methanol fuel cell (DMFC) under acidic conditions.

Complete the half-equations on the diagram and identify the species moving between the electrodes.

State the factor that limits the maximum current that can be drawn from this cell and how electrodes are designed to maximize the current.

Fuel cells have a higher thermodynamic efficiency than octane. The following table gives some information on a direct methanol fuel cell.

Determine the thermodynamic efficiency of a methanol fuel cell operating at 0.576 V.

Use sections 1 and 2 of the data booklet.

A voltaic cell consists of a nickel electrode in 1.0 mol dm⁻³ Ni²⁺ (aq) solution and a cadmium electrode in a Cd²⁺ (aq) solution of unknown concentration.

Cd (s) + Ni²⁺ (aq) → Cd²⁺ (aq) + Ni (s)               E^Θ_cell = 0.14 V

Determine the concentration of the Cd²⁺ (aq) solution if the cell voltage, E, is 0.19 V at 298 K. Use section 1 of the data booklet.

Formulate half-equations for the reactions at the anode (negative electrode) and cathode (positive electrode) during discharge of a lithium-ion battery.

Ethanol can be used in a direct-ethanol fuel cell (DEFC) as illustrated by the flow chart.

Deduce the half-equations occurring at electrodes A and B.

Electrode A: 

Electrode B:

State the name and function of X in the diagram in (b)(i).

Name:

Function:

Outline why aqueous ethanol, rather than pure ethanol, is used in a DEFC.

Outline how a microbial fuel cell produces an electric current from glucose.

C₆H₁₂O₆ (aq) + 6O₂ (g) → 6CO₂ (g) + 6H₂O (l)

The cell potential for the spontaneous reaction when standard magnesium and silver half-cells are connected is +3.17 V.

Determine the cell potential at 298 K when:

     [Mg²⁺] = 0.0500 mol dm⁻³
     [Ag⁺] = 0.100 mol dm⁻³

Use sections 1 and 2 of the data booklet.

Suggest how PEM fuel cells can be used to produce a larger voltage than that calculated in (b)(i).

Deduce the half-equations for the reactions occurring at the electrodes.

Anode (negative electrode):

Cathode (positive electrode):

Calculate the cell potential, E^θ, in V, using section 24 of the data booklet.