7-Electrolysis

Question 0

What is electrolysis?

Answer 0

The breaking down of an ionic compound, making elements, using electricity.

Question 1

When are ions free to move?

Answer 1

When ionic substances are melted/dissolved in water.

Question 2

What happens at the cathode (negative electrode)?

Answer 2

Positively charged ions gain electrons by reduction.

Question 3

What happens at the anode (positive electrode)?

Answer 3

Negatively charged ions lose electrons by oxidation.

Question 4

What is OILRIG?

Answer 4

Oxidation
Is
Less
Reduction
Is
Gain

Question 5

What is a chemical reaction with both reduction and oxidation?

Answer 5

A redox reaction.

Question 6

If the electrolyte (melted/dissolved substance) contains mix of ions how do you know what products are formed?

Answer 6

By the reactivity of the elements used.

Question 7

What is aluminium ore called?

Answer 7

Bauxite.

Question 8

What is aluminium or purified into?

Answer 8

Aluminium oxide from which aluminium is extracted.

Question 9

Why must aluminium be molten?

Answer 9

So ions are free to move.

Question 10

Why is aluminium oxide first dissolved in cryolite?

Answer 10

To lower the melting point, making it cheaper and safer.

Question 11

What happens during electrolysis of aluminium ore?

Answer 11

Electrodes made of carbon.
Aluminium ions attracted to negative electrode.
Aluminium formed at negative electrode.
Aluminium dense so sinks to bottom and is collected.
Oxide ions attracted to positive electrode.
Oxygen formed and reacts with carbon to form CO2.
Carbon electrode disappears slowly an has to be replaced.

Question 12

What is the reaction at the negative electrode when extracting aluminium from aluminium ore?

Answer 12

Al3+ + 3e- —> Al

Question 13

What is the reaction at the positive electrode when extracting aluminium from aluminium ore?

Answer 13

2O2- —> O2 + 4e-

Question 14

What is the overall reaction for extracting aluminium from aluminium ore?

Answer 14

2Al2O3 —> 4Al + 3O2

Question 15

What is produced at the positive electrode in the electrolysis of brine?

Answer 15

Chlorine gas.

Question 16

What is produced at the negative electrode in electrolysis of brine?

Answer 16

Hydrogen gas.

Question 17

What is collected at the bottom of the cell in electrolysis of brine?

Answer 17

Sodium hydroxide solution.

Question 18

What is brine?

Answer 18

Sodium chloride solution.

Question 19

What are the uses for chlorine?

Answer 19

To kill bacteria in drinking water and swimming pools.

To manufacture hydrochloric acid, disinfectants, bleach, and PVC.

Question 20

What are the uses of hydrogen?

Answer 20

Used in manufacture of ammonia and margarine.

Question 21

What are the uses of sodium hydroxide?

Answer 21

The manufacture of soap paper and ceramics.

Question 22

What is the equation for the electrolysis of brine?

Answer 22

Sodium Chloride + Water —> Chlorine + Hydrogen + Sodium Hydroxide

2NaCl + 2H2O —> Cl2 + H2 + 2NaOH

Question 23

What is the equation for what happens at the positive electrode during electrolysis of brine?

Answer 23

2Cl- —> Cl2 + 2e-

Question 24

What is the equation for what happens at the negative electrode during electrolysis of brine?

Answer 24

2H+ + 2e- ---> H2

Question 25

What are two other uses of electrolysis?

Answer 25

Electroplating. | Purification (of copper).

Question 26

Why would you electroplate an object?

Answer 26

To protect it (from corrosion. | To make it look nice.

Question 27

What do you need to purify copper using electrolysis?

Answer 27

Positive electrode made of impure copper. Negative electrode made of pure copper. Solution must contain copper ions.

Question 28

How do you purify copper during electrolysis?

Answer 28

At positive electrode copper ions pass into solution. At negative electro copper ions move towards it to gain electrons and form copper atoms which stick to pure copper electrode. Negative electrode gets bigger whilst positive dissolves into nothing. Impurities fall to bottom.

Question 29

What reaction happens at the positive electrode during purification of copper?

Answer 29

Cu ---> Cu2+ + 2e-

Question 30

What reaction happens at the negative electrode during purification of copper?

Answer 30

Cu2+ + 2e- ---> Cu

Question 31

What will be produced at the negative electrode if the metal in the solution reacts with acids to produce hydrogen?

Answer 31

Hydrogen.

Question 32

If the solution is a chloride, bromide or iodide what is produced at the positive electrode?

Answer 32

Chlorine, Bromine or Iodine.

Question 33

What are the pros of electrolysing brine?

Answer 33

3 very important materials are produced from one raw material. Brine is a renewable source that's readily available. Brine is cheap. Products formed are used in many different industries to make a variety of things. Minimal waste produced.

Question 34

What are the cons of electrolysing brine?

Answer 34

Process of electrolysis very expensive as requires lots of electrical energy. Production of electricity in power stations adds to pollution. Hydrogen and chlorine can be produced by other methods much more cheaply.