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Sodium hydroxide and chlorine are used to make bleach.

Electrolysis 2

Electrolysis of solutions depends on ion choice. This GCSE Chemistry quiz checks what forms at each electrode, and why water can compete with metal and halide ions.

Explore the Topic →

(quiz starts below)

Fascinating Fact:

For aqueous solutions, hydrogen is produced at the cathode unless the metal ion is less reactive than hydrogen. Copper solutions, for example, can produce copper metal instead.

In GCSE Chemistry, aqueous electrolysis shows that water is not just a solvent, it can affect the products. You learn how to decide what is discharged at each electrode by comparing reactivity, and how electrolysis can plate metals or release gases.

Key Terms

Aqueous solution: A mixture where a substance is dissolved in water, meaning water and dissolved ions may both take part in electrolysis.
Discharge: When an ion is turned into an atom or molecule at an electrode by gaining or losing electrons.
Electroplating: Coating an object with a layer of metal by using electrolysis so metal ions deposit onto a surface.

Frequently Asked Questions (Click to see answers)

How do you predict the products of electrolysis of an aqueous solution?

To predict the products, consider the ions present from the solute and from water. At the cathode, hydrogen forms unless the metal is less reactive than hydrogen, and at the anode either oxygen forms from hydroxide ions or a halogen forms from halide ions.

Why is hydrogen often produced at the cathode in aqueous electrolysis?

Hydrogen is often produced because water provides hydrogen ions, and for many metal ions it is easier to reduce hydrogen than to reduce the metal. Only less reactive metal ions, such as copper, are reduced instead of hydrogen.

What happens at the anode during electrolysis of sodium chloride solution?

At the anode, negative ions are oxidised. In sodium chloride solution, chloride ions can be oxidised to chlorine gas, especially in concentrated brine, releasing bubbles of chlorine at the anode.

Try These Related Quizzes

1 .

If graphite electrodes are used instead of copper in the electrolysis of copper sulfate, the equation that shows what happens at the anode is...

H₂O → H⁺ + O₂ + e^-

Cu²⁺ + 2e^- → Cu

2H₂O → 4H⁺ + O₂+ 4e^-

Cu → Cu ²⁺ +2e^-

Graphite is carbon and is a conductor of electricity and can therefore be used for making electrodes

2 .

Pick the correct half equations for the electrolysis of copper sulfate using copper electrodes.

Cathode: Cu_(s) → Cu²⁺_(aq) + 2e^-
Anode: Cu²⁺_(aq) + 2e^- → Cu_(s)

Cathode: Cu²⁺_(aq) + 2e^- → Cu_(s)
Anode: Cu_(s)→ Cu²⁺_(aq) + 2e^-

Cathode: Cu_(s) → Cu⁺_(aq) + e^-
Anode: Cu²⁺_(aq) + 2e^- → Cu_(s)

Cathode: Cu_(s) → Cu²⁺_(aq) + 2e^-
Anode: Cu⁺_(aq) + e^- → Cu_(s)

Remember, in a pair of half equations, everything needs to be balanced, just like in any symbol equation

3 .

Which of the following is NOT a use for chlorine?

Kill bacteria

Make bleach

Make PVC

Control pH

The use of chlorine to disinfect drinking water in Victorian Britain had a profound effect on health, reducing the number of people catching water borne bacterial diseases like cholera

4 .

Choose the correct half equations for the electrolysis of brine.

Anode 2Cl^- → Cl₂ + 2e^-
Cathode 2H⁺ + 2e^- → H₂

Anode Cl^- → Cl₂ + e^-
Cathode 2H⁺ + e^- → H₂

Anode 2Cl^- → Cl₂ + 2e^-
Cathode Na⁺ + e^- → Na

Anode Cl^- → Cl + 2e^-
Cathode H⁺ + e^- → H₂

Both chlorine and hydrogen are diatomic molecules

5 .

Copper can be purified using electrolysis. Pick the correct combination of components for the electrolytic cell.

Cathode: Impure copper
Anode: Pure copper
Electrolyte: Copper sulfate

Cathode: Pure copper
Anode: Impure copper
Electrolyte: Copper sulfate

Cathode: Pure copper
Anode: Pure copper
Electrolyte: Copper sulfate

Cathode: Impure copper
Anode: Pure copper
Electrolyte: Water

Copper ions in solution are attracted to the cathode, where they are deposited as copper atoms

6 .

The hydrogen produced by the electrolysis of brine is NOT used to...

make margarine

make bleach

make hydrochloric acid

make hydrogen chloride gas

Sodium hydroxide and chlorine are used to make bleach

7 .

What gas forms at the positive electrode during the extraction of aluminium?

Hydrogen

Chlorine

Nitrogen

Oxygen

This oxygen reacts with the carbon of the positive graphite electrodes forming carbon dioxide and as a result, they have to be replaced frequently

8 .

The third product from the electrolysis of brine is sodium hydroxide. This is NOT used to...

make bleach

make paper

make soap

make margarine

Hydrogen is used for hydrogenating oils to produce margarine

9 .

When an electrical current is passed through brine (sodium chloride solution), three products are formed. They are...

chlorine gas, hydrogen gas, sodium chloride solution

chloride ions, hydrogen gas, sodium hydroxide solution

chlorine gas, hydrogen gas, sodium hydroxide solution

chlorine gas, hydrogen ions, sodium hydroxide solution

All three have important uses in the chemical industry

10 .

Aluminium ore (bauxite) must be dissolved in molten cryolite before it can be electrolysed. Why?

Raise the melting point

Lower the melting point

Increase its viscosity

Reduce its viscosity

Cryolite melts at less than 1000°C, bauxite melts at over 2000°C

You can find more about this topic by visiting BBC Bitesize - Electrolysis

Author: Kate Gardiner (Chemistry Educator & GCSE Quiz Writer)

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