Here we’ll work through an example of a type 2 electrolytic cell - Electrolysis of an aqueous solution using unreactive or inert electrodes.

We’re given that an aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). b)What is the product at the cathode? c)Write the half-reaction taking place at the anode (with its E°). d)What is the product at the anode? e)Write the overall redox equation (with its E°) f)What is the minimum voltage required?

We can visualize this solution as mobile copper 2+ ions, chloride ions, and a large number of water molecules, all moving randomly. Power Supply + – e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– e–e– 1 M CuCl 2(aq) – + Anode Cathode Cl – Cu 2+ Cl – Cu 2+ H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O H H O Cl – H H O

Question (a) asks us to write the half-reaction taking place at the cathode and include its E naught value. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). b)What is the product at the cathode? c)Write the half-reaction taking place at the anode (with its E°). d)What is the product at the anode? e)Write the overall redox equation (with its E°) f)What is the minimum voltage required?

In this solution, we have Cu 2+ ions An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). Cu 2+ H 2 O Cl –

Cl minus ions Cu 2+ H 2 O Cl – An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

And aqueous means, we have water, which we’ll write in the middle. Cu 2+ H 2 O Cl – An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

We write a C minus here for the cathode Cu 2+ H 2 O Cl – C– An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

And an A+ here for the anode. Cu 2+ H 2 O Cl – C– A+ An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

At the cathode (click) either copper (II) ions will be reduced, or (click) water will be reduced. C– Cu 2+ H 2 O Cl – A+ An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

Remember, if we have an aqueous solution, (click) for the cathode, we use the overpotential arrow on the left side of the table For the Cathode In Aqueous Solution

Any cations ABOVE this overpotential arrow WILL be reduced from an aqueous solution, even though water is present. Cations ABOVE this arrow WILL be reduced from aqueous solution For the Cathode In Aqueous Solution

And any cations BELOW this overpotential arrow WILL be NOT reduced from an aqueous solution. If these are present, Water will be reduced instead. Cations ABOVE this arrow WILL be reduced from aqueous solution Cations BELOW this arrow Will be NOT reduced from aqueous solution For the Cathode In Aqueous Solution

Here’s the black arrow on the left we use for the reduction overpotential of neutral water. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

We see that the half-reaction for the reduction of Cu2+ ions to Cu solid is far above the black arrow on the left. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

So we’ll place a checkmark by the copper (II) ion indicating that it will be reduced at the cathode, rather than water. C– Cu 2+ H 2 O Cl – A+ An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°).

The half-reaction for the reduction of Cu 2+ is Cu e –  Cu (s). An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). Reduction of Cu 2+

And because it is not reversed, it’s E naught value is the same as it is on this table, volts An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). Reduction of Cu 2+

We’ll make a note of the cathode half-reaction up here. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). Cathode: Cu e –  Cu (s) E° = 0.34 V

Question (b) asks us for the product at the cathode. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). b)What is the product at the cathode? c)Write the half-reaction taking place at the anode (with its E°). d)What is the product at the anode? e)Write the overall redox equation (with its E°) f)What is the minimum voltage required? Cathode: Cu e –  Cu (s) E° = 0.34 V

The half-reaction at the cathode is Cu e –  Cu (s), An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. b)What is the product at the cathode? Cathode: Cu e –  Cu (s) E° = 0.34 V Cathode: Cu e –  Cu (s)

So the product at the cathode is solid copper. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. b)What is the product at the cathode? Cathode: Cu e –  Cu (s) E° = 0.34 V Cathode: Cu e –  Cu (s) Product at the Cathode is Solid Copper

Question (c) asks us for the half-reaction taking place at the anode, along with its E naught value. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). b)What is the product at the cathode? c)Write the half-reaction taking place at the anode (with its E°). d)What is the product at the anode? e)Write the overall redox equation (with its E°) f)What is the minimum voltage required? Cathode: Cu e –  Cu (s) E° = 0.34 V

Let’s go back to this diagram, and this time we’ll concentrate on the anode. Two possible half- reactions at the anode are (click) the oxidation of water and (click) the oxidation of chloride ions. Cu 2+ H 2 O Cl – C– A+ An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. c)Write the half-reaction taking place at the anode (with its E°).

When we’re considering the anode, we go to the right side of the reduction table. (click) In aqueous solutions for the anode half-reaction, we use this overpotential arrow on the right. For the Anode In Aqueous Solution

Remember, how it works is any anions BELOW this overpotential arrow on the right WILL be oxidized from aqueous solution at the anode of an electrolytic cell. For the Anode In Aqueous Solution Anions BELOW this arrow WILL be oxidized from aqueous solution

And any anions ABOVE this overpotential arrow on the right will NOT be oxidized from aqueous solution. If they are present, water will be oxidized instead. For the Anode In Aqueous Solution Anions BELOW this arrow WILL be oxidized from aqueous solution Anions ABOVE this arrow Will be NOT oxidized from aqueous solution

We see that that chloride ion is right below the overpotential arrow.

So that means we can put a checkmark by the chloride in this diagram, indicating that the chloride ion will be oxidized at the anode rather than water. Cu 2+ H 2 O Cl – C– A+ An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. c)Write the half-reaction taking place at the anode (with its E°).

So we use this half-reaction and since oxidation is occurring, (click) we reverse it to write the half-reaction at the anode, Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s) E° = 0.34 V

It is 2 Cl minus Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s) E° = 0.34 V

Gives Cl 2 gas Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s) E° = 0.34 V

Plus 2 electrons. Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s) E° = 0.34 V

Because the half-reaction taking place is an oxidation (click) the E naught value on the table V, (click)must have its sign switched, so the E naught value for the half-reaction at the anode, the oxidation of chloride ions, is (click) –1.36 V Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s) E° = 0.34 V

So now we’ve answered question c, the half reaction at the anode is 2Cl –  Cl 2(g) + 2e – and its E naught value is –1.36 Volts. Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s) E° = 0.34 V An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. c)Write the half-reaction taking place at the anode (with its E°).

Question (d) asks us to state the product at the anode. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). b)What is the product at the cathode? c)Write the half-reaction taking place at the anode (with its E°). d)What is the product at the anode? e)Write the overall redox equation (with its E°) f)What is the minimum voltage required? Cathode: Cu e –  Cu (s) E° = 0.34 V Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V

To answer this question, we’ll write the anode half-reaction, Cathode: Cu e –  Cu (s) E° = 0.34 V An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. d)What is the product at the anode? Anode: 2Cl –  Cl 2(g) + 2e – Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V

And we see the product at the anode is chlorine gas. Cathode: Cu e –  Cu (s) E° = 0.34 V An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. d)What is the product at the anode? Anode: 2Cl –  Cl 2(g) + 2e – Product at the Anode is Chlorine Gas Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V

In Question (e) we’re asked to write the overall redox equation along with its E naught value. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). b)What is the product at the cathode? c)Write the half-reaction taking place at the anode (with its E°). d)What is the product at the anode? e)Write the overall redox equation (with its E°) f)What is the minimum voltage required? Cathode: Cu e –  Cu (s) E° = 0.34 V Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V

We do this by writing the half-reactions at the cathode and anode, with their E naught values. Cathode: Cu e –  Cu (s) E° = 0.34 V An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V

To get the overall redox equation, we add these two half-reactions up. Cathode: Cu e –  Cu (s) E° = 0.34 V An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V

We see that the electrons gained by the copper ion are equal to those lost by the chloride ions An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation

So we can cancel out the electrons. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation

On the left side, we have Cu 2+ and 2Clminus, An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation

And on the right side, we have Cu (solid) and Cl 2 (gas). You can see that in this electrolysis, we have decomposed the compound CuCl 2 into its elements in elemental form An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation

To get the E naught value for the overall redox reaction, we add 0.34 Volts and negative 1.36 volts, to give us (click) negative 1.02 volts. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation

This value, the –1.02 Volts, is called the E naught value for the overall redox reaction and it can also be called the overall cell potential. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation This is called the E° for the redox reaction, or the overall cell potential

The negative value confirms that the reaction is non-spontaneous, which is the case for all electrolytic cells. An external voltage must be applied to keep these operating. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. e)Write the overall redox equation (with its E°) Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation This is called the E° for the redox reaction, or the overall cell potential

Question (f) asks us to state the minimum voltage required to make this reaction occur. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. a)Write the half-reaction taking place at the cathode (with its E°). b)What is the product at the cathode? c)Write the half-reaction taking place at the anode (with its E°). d)What is the product at the anode? e)Write the overall redox equation (with its E°) f)What is the minimum voltage required? Cathode: Cu e –  Cu (s) E° = 0.34 V Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V

The minimum voltage required for an electrolytic cell is the positive voltage needed to overcome the negative tendency for the overall redox reaction to occur, so in this case it is (click) volts An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. f)What is the minimum voltage required? Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation Minimum Voltage Required = 1.02 V

It should be noted that even though 1.02 volts is the MINIMUM voltage needed, in actual practice,(click)the voltage used for an effective reaction is considerably higher than this. An aqueous solution of copper(II) chloride (CuCl 2(aq) ) is electrolyzed using inert carbon electrodes. f)What is the minimum voltage required? Anode: 2Cl –  Cl 2(g) + 2e – E° = –1.36 V Cathode: Cu e –  Cu (s). E° = 0.34 V : Cu Cl –  Cu (s) + Cl 2(g) E° = –1.02 V Overall Redox Equation Minimum Voltage Required = 1.02 V For an effective reaction, the voltage used is much higher