Unit 2: 5.4 - Electrolysis

Question 1

What is electrolysis?

Answer 1

The process that uses electricity to break down ionic compounds into elements.

Question 2

What is the name of the substance which is broken down?

Answer 2

The electrolyte

Question 3

What type of substance are the electrodes made of? Give an example.

Answer 3

An inert subtance. E.g. Carbon

Question 4

Negatively charged ions move towards which electrode?

Answer 4

The anode, (+)

Question 5

Positively charged ions move to which electrode?

Answer 5

The cathode, (-)

Question 6

Positively charged ions form which atoms during electrolysis?

Answer 6

Metal or hydrogen, depending on which ions are present.

Question 7

Negatively charged ions form which atoms during electrolysis?

Answer 7

Non-metallic

Question 8

What state must the ionic compound be in during electrolysis and why?

Answer 8

Liquid (l) or in an aqueous solution (aq) so the electrons are able to freely move around and conduct electricity.

Question 9

State the processes undergone by molten lead bromide during electrolysis.

Answer 9

The lead attracts to the anode, where is gains an electron. The bromide goes to the cathode, where it loses an electron, and becomes bromine gas.

Question 10

What is reduction?

Answer 10

Reduction Is Gain (of electrons) (OILRIG)

Question 11

What is oxidisation?

Answer 11

Oxidisation Is Loss (of electrons) (OILRIG)

Question 12

Complete the half equation for chlorine:

2Cl- –> ….+….

Answer 12

2Cl- –> 2e- + 2Cl

Question 13

Under what circumstances is hydrogen formed at the cathode?

Answer 13

When solutions of ions water are electrolysed and if the other positive ions in the solution are those of a metal MORE reactive than hydrogen.

Question 14

What is usually produced at the anode from aqueous solutions?

Answer 14

Oxygen

Question 15

When is a halogen sometimes produced at the anode?

Answer 15

If the solution contains a reasonably high concentration of halide ions.

Question 16

Why must aluminium be extracted using electrolysis?

Answer 16

It is more reactive than carbon.

Question 17

What ionic compound is aluminium oxide added to during electrolysis?

Answer 17

Cyrolite.

Question 18

What is the normal melting point for aluminium and why is this not good?

Answer 18

2000 degrees Celsius. This is bad as it would require lots of energy.

Question 19

What temperature is aluminium oxide electrolysed at?

Answer 19

850 degrees Celsius.

Question 20

Give the symbol and word equation for the electrolysis of aluminium oxide.

Answer 20

2Al2O3(l) –>4Al (l) + 3O2 (g)

Aluminium oxide –> Aluminium + Oxygen

Question 21

Give the half equations of almunium oxide at the negative and positive electrode.

Answer 21

-: Al3+ (l) + 3e- –> Al (l)

+: 2O2- (l) –> 2O2 (g) + 4e-

Question 22

How do the high temperatures effect the carbon electrodes?

Answer 22

The oxygen bonds with the carbon producing CO2, meaning they have to be replaced regularly.

Question 23

Which ions does brine contain?

Answer 23

Na+, Cl-, H+, OH- (all aq)

Question 24

What is released from brine at each electrode?

Answer 24

Anode: Chlorine. Cathode: Hydrogen

Question 25

What is left after the electrolysis of brine?

Answer 25

A solution of sodium ions and hydroxide ions, NaOH (aq), sodium hydroxide

Question 26

What are the products of the electrolysis of brine used for?

Answer 26

Hydrogen: Hardening oils (e.g. making margarine) and Hydrochloric acid. Chlorine: Used as a disinfectant and bleach, as well as used to make plastics. Sodium hydroxide: Soap, Paper, Neutralising acids (as it's a strong alkali).

Question 27

Give 4 uses of electroplating

Answer 27

- To make an object more attractive - Corrosion protection - Increasing the hardness of an object - Reduce costs by just using a thin layer.

Question 28

The object to be electroplated is used as which electrode?

Answer 28

The negative, as the positive metal ions will be attracted to it.

Question 29

How is the metal plated onto the other metal?

Answer 29

The ions in the solution are attracted to the negative electrode. These become neutral atoms and are held on by metallic bonding.

Question 30

The object which is to be used as a plating metal is used as which electrode?

Answer 30

The positive

Question 31

What does the electrolyte need to contain in electroplating?

Answer 31

Ions of the plating metal.

Question 32

Describe the process during electroplating

Answer 32

- At the anode, atoms of the plating metal lose electrons to form metal ions which enter the solution. - At the cathode, +ive metal ions gain electrons which plate onto the cathode.