C6- Electrolysis

Question 1

Electrolysis

Answer 1

Breaking down ionic compounds using electricity

Question 2

Electrolyte

Answer 2

The ionic compound broken down (solution)

Question 3

Why cant the electrolyte be a solid?

Answer 3

This is because the ions in a solid are not free to move due to the strong electrostatic forces of attraction ( and if not free then electricity doesn’t flow)

Question 4

Whats the cathode?

Answer 4

The negative electrode

Question 5

Whats the anode?

Answer 5

The positive electrode

Question 6

What are the electrodes made off?

Answer 6

Carbon

Question 7

What happens at the anode?

Answer 7

Oxidations

Question 8

What happens at the cathode?

Answer 8

Reduction

Question 9

Whats aluminium useful for?

Answer 9

Pans, cooking foil, aeroplanes, drink cans, car bodies, bicycle frames…

Question 10

Whats the name of Aluminium’s metal ore?

Answer 10

Bauxite

Question 11

Whats the aluminium oxide mixed with for electrolysis?

Answer 11

Molten cryolite

Question 12

Why is aluminium oxide mixed with molten cryolite?

Answer 12

To lower the melting point and this will reduce the amount of energy needed and save money

Question 13

Whats forms at the cathode when Aluminium is electrolysed?

Answer 13

Aluminium

Question 14

What forms at the Anode when aluminium is electrolysed ?

Answer 14

Oxygen

Question 15

Whats the half equation for the reaction at the Cathode ( electrolysis of aluminium)?

Answer 15

AL3+(L)+ 3e- —— -> AL(L)

Question 16

Whats the half equation for the reaction at the Anode ( electrolysis of aluminium)?

Answer 16

2O2- (L) ——-> O2 (g) + 4e-

Question 17

Why do the carbon anodes have to be replaced regularly (electrolysis of aluminium)

Answer 17

Because they regularly burn away as the oxygen reacts with the carbon anodes forming carbon dioxide gas

Question 18

During electrolysis of aqueous solutions where the H+ and OH- ions come from?

Answer 18

When the water breaks down

Question 19

During electrolysis of aqueous solutions what forms at the cathode?

Answer 19

The less reactive element between the positive ions ( either hydrogen or the metal) you use the reactivity series

Question 20

During electrolysis of aqueous solutions what forms at the anode?

Answer 20

OH- (hydroxide) is given off unless the electrolyte id a solution of a halide (group 7) if so a halogen is given off

Halide> hydroxide> all other negative charged ions

Question 21

What is brine?

Answer 21

concentrated sodium chloride solution

Question 22

What is the word equation for the electrolysis of brine (sodium chloride solution)?

Answer 22

Sodium chloride solution —> hydrogen gas+ chlorine gas+ sodium hydroxide solution

Question 23

What forms at the cathode during the electrolysis of brine?

Answer 23

Hydrogen (H+) ions gain 1 electron (reduced). The hydrogen atoms bond together in pairs and give off hydrogen gas

Question 24

What forms at the anode during the electrolysis of brine?

Answer 24

Chlorine atoms lose 1 electron (oxidised). The chlorine atoms bind together in pairs and give ofd chlorine gas

Question 25

Whats the half equation at the cathode during the electrolysis of brine (sodium chloride solution)?

Answer 25

2H+(aq) + 2e- ------> H2(little 2 not a charge)

Question 26

Whats the half equation at the anode during the electrolysis of brine (sodium chloride solution)?

Answer 26

2CL- (aq) -----> CL2 +2e-

Question 27

Whats the lab test for chlorine gas ?

Answer 27

Bleaches damp litmus paper white

Question 28

Whats the lab test for hydrogen gas?

Answer 28

Squeaky 'pop' with lighted splint

Question 29

Whats the lab test for oxygen ?

Answer 29

Relights glowing splint

Question 30

Name 3 control variables/ precautions when investigating the electrolysis of a solution?

Answer 30

- don't let the 2 electrodes touch each other as a short circuit would be produce pd - wear gloves and eye protection - use a lid to ensure the gas doesn't escape - pay close attention to gases being produces as the volume of them will be very small

Question 31

What are the observations and element formed at the Anode during the electrolysis of copper (II) chloride?

Answer 31

Bubbles, chlorine

Question 32

What are the observations and element formed at the Cathode during the electrolysis of copper (II) chloride?

Answer 32

Colour change, copper

Question 33

What are the observations and element formed at the Anode during the electrolysis of copper (II) sulfate?

Answer 33

Bubbles ,oxygen

Question 34

What are the observations and element formed at the Cathode during the electrolysis of copper (II) sulphate?

Answer 34

Colour change, copper

Question 35

What are the observations and element formed at the Anode during the electrolysis of sodium chloride?

Answer 35

Bubbles, chlorine

Question 36

What are the observations and element formed at the Cathode during the electrolysis of sodium chloride?

Answer 36

Bubbles, hydrogen

Question 37

What are the observations and element formed at the Anode during the electrolysis of sodium sulfate?

Answer 37

Bubbles, oxygen

Question 38

What are the observations and element formed at the Cathode during the electrolysis of sodium sulfate ?

Answer 38

Bubble, hydrogen

Question 39

Explain why carbon electrodes can conducted electricty

Answer 39

It has delocolised electrons that are free to move throughout the structure

Question 40

Whats the half equation at cathode in the electrolysis of lead bromide?

Answer 40

Pb-----> Pb2+ + 2e-

Question 41

Whats the half equation at anode in the electrolysis of lead bromide?

Answer 41

2Br- + 2e- --------> 2Br-