C2 - Electrolysis

Question 0

Why is electrolysis more complicated in aqueous solutions?

Answer 0

Because ions in the water are present as well as the ions in the compound

Question 1

What is brine?

Answer 1

Sodium chloride solution

Question 2

What will form at the positive electrode if possible?

Answer 2

A halogen

Question 3

What is electrolysis?

Answer 3

The breakdown of a substance by passing electricity through it

Question 4

How do you remember the difference between oxidation and reduction?

Answer 4

OIL RIG
Oxidation is loss (of electrons)
Reduction is gain (of electrons)

Question 5

What 2 chemical properties are needed to use electrolysis in breaking down of a substance?

Answer 5

Substance is ionic

Ions are free to move

Question 6

What are the cathode and anode?

Answer 6

Anode is positive electrode

Cathode is negative electrode

Question 7

What is a half equation?

Answer 7

A chemical equation that shows how an ion gains or loses electrons at an electrode
2H+ + 2e- –> H^2
2Cl- –> Cl^2 + 2e-

Question 8

What does diatomic mean?

Answer 8

An element that naturally has 2 covalently bonded atoms such as H^2

Question 9

Which substances made by electrolysis are diatomic?

Answer 9

Hydrogen at the cathode

Halides at the anode

Question 10

How do OH- ions oxidise? (Chemical equation)

Answer 10

4OH- –> O^2 + 2H^2O + 4e-

Question 11

What is Faraday’s law of electrolysis?

Answer 11

The higher the current used, the faster the substance is produced

Question 12

What is an electrolyte?

Answer 12

An ionic substance that is either a liquid or dissolved in water

Question 13

Why isn’t an ionic solid an electrolyte?

Answer 13

The ions are not free to move so the current cannot pass through them

Question 14

What are the 4 uses of electrolysis?

Answer 14

Extract a metal from an ore
Purify copper
Create substances from salt
Improve surface of a metal

Question 15

Why is electrolysis avoided if possible?

Answer 15

Expensive due to the cost of the electricity as a high current is needed

Question 16

Why is electrolysis used for purifying copper?

Answer 16

Copper needs to be very pure for use as electrical wiring

Question 17

Show how sodium chloride solution would break down in electrolysis

Answer 17

Hydrogen is less reactive so at the negative electrode, the H+ ions lose their charge
Because a halogen will form at the positive electrode if possible, the Cl- ions will lose their charge and become the halogen chlorine
When the electricity is turned off, the Na+ and OH- ions are left so they react to form sodium hydroxide

Question 18

What are the rules about reactions at the negative electrode?

Answer 18

If metal ions and hydrogen ions are present, the metal ions will stay in solution and hydrogen will form if the metal is more reactive than hydrogen

This is because, the more reactive an element, the keener it is to stay as ions

Question 19

What are the rules about reactions at the positive electrode?

Answer 19

If hydroxide and halide ions are present, halogens will be produced and the hydroxide will stay as ions

If no halide is present, oxygen will be formed

Question 20

What are the 2 reasons that the electrolysis of sodium chloride solution is useful in industry?

Answer 20

Chlorine is useful in bleach and plastics

Sodium hydroxide is a very strong alkali and used widely in the chemical industry

Question 21

Why is electrolysis of aluminium oxide so expensive and what is done to counter this?

Answer 21

It has to be heated up to 2000C for it to become molten

Cryolite (less common aluminium ore) is added and this brings the melting point down to 900C

Question 22

Why does the positive electrode have to be replaced?

Answer 22

When oxygen forms at the electrode, it reacts with the carbon of the electrode and forms carbon dioxide

This reaction eats away the carbon of the electrode

Question 23

Describe electroplating

Answer 23

You can coat the surface of one metal with another metal

The negative electrode is the metal to be plated and the positive electrode is the metal that will plate it. The electrolyte also contains the ions if the playing metal

The ions that plate the metal come from the solution and the positive electrode keeps the solution topped up

Question 24

What are the 2 reasons for electroplating?

Answer 24

Decoration (plate a cheap metal with an expensive metal to make it look expensive)

Conduction (copper often plates metals for electronic circuits because it conducts electricity so well)