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School Chemistry: Describing & explaining electrolysis of copper chloride solution

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ELECTROLYSIS of COPPER CHLORIDE SOLUTION

(Suitable for AQA, Edexcel and OCR GCSE chemistry students)

ELECTROCHEMISTRY revision notes on electrolysis, cells, experimental methods, apparatus, batteries, fuel cells and industrial applications of electrolysis

6. Using an electrolysis cell - investigating the electrolysis of copper(II) chloride solution

A simple method of investigating the electrolysis of copper(II) chloride solution is described. The formation of the products of electrolysing aqueous copper chloride is fully explained with the appropriate electrode equations.  What are the products of the electrolysis of aqueous copper chloride solution?

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6. Electrolysis of copper(II) chloride solution

The products of electrolysing copper chloride solution are copper metal and chlorine gas

In the simple electrolysis cell (left diagram), the graphite (carbon) electrodes are, through a large rubber bung, 'upwardly' dipped into an solution of dilute copper chloride.

In this cheap and simple apparatus the gaseous product (chlorine) is collected in a small test tube inverted over the carbon electrodes. You have to fill the little test tubes with the electrolyte (copper chloride solution), hold the liquid in with your finger and carefully invert them over the nearly full electrolysis cell.

The electrolysis will only take place when electricity is passed through the dilute copper(II) chloride solution. The platinum or carbon electrodes are inert. You can also use the simple electrolysis set-up illustrated below (right) using two inert metal wires as electrodes.

The electrolyte copper(II) chloride, provides a high concentration of copper(II) ions Cu2+ and chloride ions Cl– to carry the current during the electrolysis process.

The tiny traces of hydrogen ions (H+) and hydroxide ions (OH–) from water, would not normally be discharged at the electrodes in this investigation.

The electrolysis will only take place when electricity is passed through the copper chloride solution.

The electrode reactions and products of the electrolysis of copper chloride solution are illustrated by the theory diagram above

Note: The majority of liquid water consists of covalent H2O molecules, but there are trace quantities of H+ and OH– ions from the reversible self–ionisation of water: H2O(l) H+(aq) + OH–(aq)

The half-equations for the electrolysis of copper(II) chloride solution (the electrolyte)

(a) The negative cathode electrode reaction for the electrolysis of copper(II) chloride solution

The positive copper(II) ions Cu2+ (from copper sulfate) and the H+ ions (from water) are attracted to the negative cathode.

Only the copper(II) ion is discharged (preferentially).

The less reactive a metal, the more readily its ion is reduced on the electrode surface.

a reduction electrode reaction

Cu2+(aq) + 2e– ==> Cu(s) (copper deposit)

positive ion reduction by electron gain

This is a reduction reaction because the copper ions gain electrons, i.e. the copper ions are reduced to copper.

(b) The positive anode electrode reaction for the electrolysis of copper chloride solution

The (+) anode attracts the OH– (from water) and Cl– ions (from copper chloride).

Only the chloride ion is discharged preferentially  in appreciable quantities.

Chloride ions are oxidised by electron loss to form chlorine gas at the positive electrode.

2Cl–(aq) – 2e– ==> Cl2(g)

 or  2Cl–(aq) ==> Cl2(g) + 2e– 

negative ion oxidation by electron loss

This is an oxidation reaction because the chloride ions lose electrons i.e. the chloride ions are oxidised to chlorine molecules.

Extra COMMENTS on the electrolysis of copper(II) chloride solution

Overall equation for the electrolysis of aqueous copper chloride: CuCl2(aq) ===> Cu(s) + Cl2(g)

This could be written more accurately as an ionic equation: Cu2+(aq) + 2Cl–(aq) ===> Cu(s) + Cl2(g)

SUMMARY OF PRODUCTS FROM THE ELECTROLYSIS OF COPPER(II) CHLORIDE SOLUTION

with inert carbon (graphite) electrodes or inert platinum electrodes

Electrolyte negative cathode product negative electrode

cathode half-equation

positive anode product positive electrode

anode half-equation

Copper(II) chloride

HCl(aq)

copper deposit Cu2+(aq) + 2e– ==> Cu(s) chlorine gas

2Cl–(aq) – 2e– ==> Cl2(g)

 or  2Cl–(aq) ==> Cl2(g) + 2e– 

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Electrolysis Quiz (GCSE 9-1 HT Level (harder)

Electrolysis Quiz (GCSE 9-1 FT Level (easier)

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