CC10

Question 1

What is electrolysis?

Answer 1

Electrolysis is splitting up substances using electricity.

Question 2

What is the substance broken down by electrolysis called?

Answer 2

The substance that is broken down by electrolysis is called the electrolyte.

Question 3

What is an electrolyte?

Answer 3

Ionic compound in molten or dissolved solution that conducts the electricity.

Question 4

How is electricity conducted in electrolysis?

Answer 4

When an ionic solid is melted or dissolved in water, its ionic bonds break. This allows the ions to move. An ionic substance with freely moving ions is called an electrolyte and can conduct electricity.

Question 5

What happens in electrolysis in order to decompose electrolytes?

Answer 5

Electrolysis uses energy transferred by electricity to decompose electrolytes.

Question 6

What is an electrode?

Answer 6

A rod of metal or graphite through which an electric current flows into or out of an electrolyte.

Question 6

How do electrodes work?

Answer 6

Two electrodes are connected to a direct current (d.c.) electric supply and placed into the electrolyte. The two types of ions carry opposite charges and so migrate towards the electrode with the opposite charge.

Question 6

What ions are attracted to what electrodes?

Answer 6

• Cations are positive ions and are attracted to the negative cathode.
• Anions are negative ions and are attracted to the positive anode.

Question 7

What is Oxidation and where does it happen?

Answer 7

At the anode, negative ions lose electrons which is oxidation.

Question 8

What is Reduction and where does it happen?

Answer 8

At the cathode, electrons are transferred from the electrode to the positive ions which is reduction.

Question 9

What is the acronym to remember Oxidation and Reduction?

Answer 9

O - Oxidation
I - Is
L - Loss of electrons
R - Reduction
I - Is
G - Gain of electrons
(OILRIG)

Question 10

What does the transfer of electrons in electrolysis cause?

Answer 10

This transfer of electrons changes charged ions into atoms or molecules, resulting in chemical changes at the electrodes (e.g. Zinc chlorine are attracted to the cathode, where they’ll gain electrons and become Zinc atoms. At the same time Cl⁻ ions migrate to the anode, where they will lose electrons and become chlorine molecules.

Question 11

What changes does charged ions undergo during Oxidation and Reduction?

Answer 11

Reduction = Gains electrons, Becomes atoms
Oxidation = Loses electrons, Becomes molecules.

Question 12

What are half equations?

Answer 12

A chemical equation written to describe an oxidation or reduction half-reaction.

Question 13

What is the half equation for Zn²⁺ and Cl⁻?

Answer 13

Cathode reaction: Zn²⁺ + 2e –> Zn reduction (2 electrons needed for full shell)
Anode reaction: 2Cl⁻ –> Cl₂ + 2e oxidation (2 Cl⁻ ions needed to form one chlorine molecule)

Question 14

Do half equation practice questions.

Answer 14

Look at half equation practice questions.

Question 15

What happens during electrolysis of Copper Sulfate Solution?

Answer 15

During electrolysis, the copper atoms in the anode lose two electrons each to become copper ions. These ions dissolve in the solution and migrate to the cathode, where they are deposited as pure copper. So, the impure copper anode loses mass and the pure copper cathode gains mass. Impurities from the anode do not form ions and collect below the anode as ‘sludge’. The anode sludge is collected because it may contain valuable metallic elements.

Question 16

What are inert electrodes?

Answer 16

Unreactive electrodes.

Question 17

What type of electrodes is electrolysis usually carried out with?

Answer 17

The electrolysis of molten or dissolved ionic salts is carried out using inert electrodes (usually graphite or platinum).

Question 18

What happens when a molten salt is electrolysed?

Answer 18

When a molten salt is electrolysed, ions are discharged as atoms or molecules at the electrodes.

Question 19

What happens when molten lead bromide is electrolysed?

Answer 19

When molten lead bromine is electrolysed, Bromine is produced at the anode and lead is produced at the cathode.

Question 20

What are the half equations for molten lead bromide?

Answer 20

Cathode reaction: Pb²⁺(l) + 2e –> Pb(l) Reduction
Anode reaction: 2Br⁻(l) –> Br₂(g) + 2e Oxidation

Question 21

What is the half equation for Copper sulfate solution?

Answer 21

Cathode reaction: Cu²⁺(aq) +2e⁻ –> Cu(s) Reduction
Anode reaction: Cu(s) –> Cu²⁺(aq) + 2e⁻ Oxidation

Question 22

Where is the metal and non-metal produced in electrolysis?

Answer 22

The metal is produced at the cathode and the non-metal is produced at the anode.

Question 23

Describe electrolysis for copper chloride solution?

Answer 23

Ions: Cu²⁺(aq) and Cl⁻(aq) (from salt), H⁺(aq) and OH⁻(aq) (from water)

Cathode: Cu²⁺(aq) and H⁺(aq) ions are attracted. Copper ions are discharged more readily than hydrogen ions, so copper is formed as a brown solid. (Cu²⁺(aq) + 2e –> Cu(s) is a reduction)

Anode: Cl⁻(aq) and OH⁻(aq) ions are attracted. Chloride ions are discharged more readily than hydroxide ions, so chlorine is formed as a pale green gas (2Cl⁻(aq) –> Cl₂(g) + 2e is an oxidation)

Overall: The copper chloride decomposes but the water does not change (CuCl₂(aq) –> Cu(s) + Cl₂ (g))

Question 24

Describe electrolysis for sodium chloride solution?

Answer 24

Ions: Na⁺(aq) and Cl⁻(aq) (from salt), H⁺(aq) and OH⁻(aq) (from water)

Cathode: Na⁺(aq) and H⁺(aq) ions are attracted. Hydrogen ions are discharged more readily than sodium ions, so hydrogen gas is formed (2H⁺(aq) + 2e –> H₂(g) which is a reduction)

Anode: Cl⁻(aq) and OH⁻(aq) ions are attracted. Chloride ions are discharged more readily than hydroxide ions, so chlorine is formed as a pale green gas (2Cl⁻(aq) –> Cl₂(g) + 2e which is an oxidation)

Question 25

How can copper be purified using electrolysis?

Answer 25

Copper can be purified by the electrolysis of copper sulfate solution using copper electrodes. The copper atoms in the anode lose electrons to become copper ions. These dissolve in the solution and migrate to the cathode, where they are deposited as pure copper. Impurities from the anode do not form ions and collect below the anode as ‘sludge’.