19.1 Electrochemical Cells

Use section 24 of the data booklet and the information below to determine if the following reaction is feasible at 298 K.

2KMnO₄ (aq) + 5H₂O₂ (aq) + 6HCl (aq) → 2MnCl₂ (aq)+ 8H₂O (l) + 5O₂ (g) + 2KCl (aq)

   O₂ (g) + 2H⁺ + 2 e^-  Η₂O₂    E^θ = 0.68 V

The reaction of copper oxide and sulfuric acid is shown below. Use section 24 of the data booklet to explain why the reaction is thermodynamically feasible.

Suggest a reason why the reaction does not occur despite being thermodynamically feasible.

A student set up a electrolytic cell using a concentrated sodium chloride solution using a current of 6 amps. 

State the half-equations occurring at the electrodes during the electrolysis of the concentrated aqueous solution of sodium chloride.

Cathode ..................................................................................................

Anode ....................................................................................................

Use section 2 of the data booklet to determine the time, in minutes, to produce 2.00 dm³ of gas at the anode at standard temperature and pressure. State your answer to 2 significant figures. 

The student changed the electrolyte to a very dilute sodium chloride solution. State what change would occur at the anode and give the half equation for the process.

In a different electrolysis experiment, copper sulfate solution was electrolysed using graphite electrodes. Using section 24 of the data booklet explain how the products at the anode and cathode are produced. 

Explain why the following does not represent the standard hydrogen electrode.

The standard electrode potential for Zn²⁺ (aq) + 2e^- → Zn (s) is –0.76 V. State the meaning of the minus sign in the value of –0.76 V.

Zinc coating on metals serves as physical protection which prevents rust from affecting the underlying metal surface. This is achieved by electroplating.
 

Use sections 2 and 6 of the data booklet to determine the length of time, in hours, a 0.1 A current required to deposit 1.0 g of zinc on the item to be electroplated. State your answer to 2 significant figures. 

Using section 24 of the data booklet deduce the full equation for the Cr₂O₇^2- (aq) / Cr³⁺ (aq) and Br₂ (l) / Br^- (aq) cell.

Determine the value for E^Θcell value for the cell outlined in part a). 

Use your answer to part b) and sections 1 and 2 of the data booklet to determine whether the reaction in part a) reaction is spontaneous.

An electrochemical cell has a free energy change of -14.475 kJ mol^-1. Use the information in the table to determine the cell representation of the electrochemical cell. 

Aqueous copper(II) sulfate can be electrolysed using passive or active electrodes. Passive electrodes can be made of platinum and active electrodes from copper. 

Draw a labelled diagram of an electrolytic cell for this process using platinum electrodes and identify in which direction electrons flow.

Write the half equations taking place at each electrode in part a), including state symbols, and state what is seen at each electrode.

Write the half equations taking place at each electrode when using copper electrodes, including state symbols, and state what is seen at each electrode.

State what happens to the colour and acidity of the electrolyte when using platinum and copper electrodes in the electrolysis of aqueous copper(II) sulfate.

Iron(II) bromide can be electrolysed in the liquid state. Describe two ways in which the current is conducted in an electrolytic cell.

A current of 2.00 A flows for 20 minutes in a cell containing molten iron(II) bromide.

Write the half reaction equations at the electrodes and determine the mass of iron and bromine produced.

If iron(III) bromide was used in place of iron(II) bromide in part b) determine the differences in the mass of iron and bromine produced.

State and explain the products of electrolysing dilute iron(II) bromide.

State the conditions under which the EMF of a redox reaction will be spontaneous.

Using Sections 1 &  24 of the Data Booklet, calculate ΔGᶿ for the following reaction and state whether the reaction is spontaneous under standard conditions.

 Fe²⁺ (aq) + Ni(s) → Fe(s) + Ni²⁺ (aq)

Suggest, with a reason, how a non-spontaneous reaction could be made spontaneous.

Using Table 2, predict and write overall equations for all the spontaneous reactions. 

Table 2

Metals coatings on other metals can be achieved using electroplating. Three beakers containing solutions of Sn(NO₃)₄, Co₂(SO₄)₃, Pb(NO₃)₂, were set up as electrolytic cells and used to electroplate the metals. The same amount of current was passed through the cells for the same length of time.           

State and explain in which cell would the greatest amount of metal be produced and identify the electrode where the metals are deposited. 

Apart from current and time, identify two factors that influence the amount of cobalt deposited in the Co₂(SO₄)₃ cell.

State two reasons why electroplating of metals is carried out.

A nickel teaspoon is electroplated with silver using sodium argentocyanide. Predict the mass changes at each electrode.