Electrolysis

Question 1

Define electrolysis

Answer 1

splitting up of a substance into its elements using electricity

Question 2

What type of substance can undergo electrolysis?

Answer 2

ionic compounds as they can be made to conduct electrcity

Question 3

A substance can only be electrolysed once…

Answer 3

melted as ions are free to move
or dissolve in water

Question 4

Why are electrodes needed? What are they made of?

Answer 4

needed to complete the circuit
made of graphite which can conduct electricity and has low reactivity

Question 5

What is the positive electrode called?

Answer 5

anode

Question 6

What is the negative electrode called?

Answer 6

cathode

Question 7

What happens during molten electrolysis?

Answer 7

electrolyte heated (ensure compound stays heated)
anode attracts anions (-)
cathode attracts cations (+)

Question 8

molten magnesium bromide (electrolyte)
What are the half equations?
Mg⁺² and Br⁻¹

Answer 8

Br⁻¹ goes to anode
2Br⁻¹ → 2e⁻ +Br₂

Mg⁺² goes to cathode
Mg⁺² + 2e⁻ → Mg

Question 9

molten magnesium bromide
What is observed at each electrode?

Answer 9

negative electrode:
Mg ion gains 2e⁻ to form Mg atom so grey solid formed

positive electrode:
bubbles, brown gas given off

Question 10

What are the negatives of molten electrolysis?

Answer 10

Requires lots of energy ∴ expensive
↳ environmental problems

Question 11

Why is copper a good conductor of electricity?

Answer 11

has delocalised electrons that can move

Question 12

KCl (K⁺, Cl⁻)
What are the half equations? What is observed at each electrode?

Answer 12

negative:
K⁺ + e⁻ → K
(grey solid)

positive:
2Cl⁻ →Cl₂ + 2e⁻
(bubbles, green gas)

Question 13

MgO (Mg⁺², O⁻²)
What are the half equations? What is observed at each electrode?

Answer 13

negative:
Mg⁺² + 2e⁻ → Mg
(grey solid)

positive:
2O⁻² → 4e⁻ + O₂
(bubbles)

Question 14

AgI (Ag ⁺¹, I ⁻¹)
What are the half equations? What is observed at each electrode?

Answer 14

negative:
Ag⁺¹ + e⁻ → Ag
(silver solid)

positive:
2I⁻¹ → 2e⁻ + I₂
(bubbles, purple gas)

Question 15

Fe₂O₃ (Fe⁺³, O⁻²)

Answer 15

negative:
Fe⁺³ + 3e⁻ → Fe
(grey solid)

positive:
2O⁻² → 4e⁻ + O₂
(bubbles)

Question 16

PbBr₂ (Pb⁺², Br⁻)
What are the half equations? What is observed at each electrode?

Answer 16

negative:
Pb⁺² + 2e⁻ → Pb
(grey solid)

positive:
2Br⁻ → 2e⁻ + Br₂
(bubbles, brown gas)

Question 17

Solution electrolysis
Positive electrode rule?

Answer 17

Halogen or oxygen
Halogen takes priority

Question 18

Solution electrolysis
Negative electrode rule?

Answer 18

X or hydrogen is produced
The less reactive one is produced

Question 19

What is produced in this solution electrolysis?
NaCl

Answer 19

Positive electrode:
(Cl⁻, OH⁻)
Cl₂ produced
2Cl⁻ → 2e⁻ + Cl₂

Negative electrode:
(Na⁺, H⁺)
Na more reactive ∴ H produced
2H⁺ + 2e⁻ → H₂

Left over: NaOH

Question 20

What is produced in this solution electrolysis?
CuSO₄

Answer 20

positive electrode:
4OH⁻ → O₂ + 2H₂O + 4e⁻
observations: bubbles

negative electrode:
Cu⁺² + 2e⁻ → Cu
observations: brown solid

Whats left?
H₂SO₄