Electrolysis

Question 1

Define the term “Electrolysis”

Answer 1

The process of using electricity to split apart ionic compounds.

Question 2

What is the term used to describe the substance being electrolysed?

Answer 2

The electrolyte

Question 3

Why does a substance need to be dissolved or melted for electrolysis to take place?

Answer 3

Because the ions in the substance need to be free to move in order to move to the electrodes (and conduct electricity).

Question 4

What is the basic apparatus for electrolysis?

Answer 4

• Power source connected in a circuit with the electrodes:
  | Negative electrode (cathode)
  | Positive electrode (anode)
• Container
• The electrolyte: the compound to be split up

Question 5

What happens to ions of different charge during electrolysis?

Answer 5

• Positive ions (metal) move to the cathode (negative charge).
• Negative ions (non-metal) move to the anode (positive charge).

Question 6

What happens to the ions when they reach the oppositely charged electrode?

Answer 6

• Negative ions lose electron(s) and become neutral atoms which is REDUCTION.
• Positive ions gain electron(s) and become neutral atoms which is OXIDATION.

Question 7

What does OILRIG stand for?

Answer 7

Oxidation
Is
Loss (of electrons)
Reduction
Is
Gain (of electrons)

Question 8

If there are a mixture of positive ions which one will react during electrolysis?

Answer 8

The one that forms the least reactive element (look and use the data sheet for reference)

Question 9

Complete this half equation:
Cl⁻→ Cl₂

Answer 9

2Cl⁻ → Cl₂ + 2e⁻

Question 10

Complete this half equation:
Al³⁺ → Al

Answer 10

Al³⁺ + 3e⁻ → Al

Question 11

What starting material is used to make Aluminium using electrolysis? (3:05)

Question 12

Why is cryolite added to the reaction (during the extraction of Aluminium oxide)? (2)

Answer 12

• To lower the melting point / reaction temperature
• Therefore less energy is needed (and it will be less costly).

Question 13

What is formed at the positive and negative electrodes (during the extraction of Aluminium oxide)?

Answer 13

• Aluminium is formed at the negative electrode.
• Oxygen, O₂(g), is formed at the positive electrode.

Question 14

Why are graphite electrodes used (during the extraction of Aluminium oxide)? (2)

Answer 14

• Good conductors of electricity
• Relatively unreactive compared to metals used.

Question 15

Why do the graphite electrodes need replacing? (2)

Answer 15

Carbon in the graphite reacts with the oxygen to form carbon dioxide; the electrode is slowly worn out.

Question 16

What 3 products are formed from the electrolysis of sodium chloride solution, NaCl(aq)?

Answer 16

• Hydrogen, H₂(g) - negative electrode
• Chlorine, Cl₂(g) - positive electrode
• Sodium hydroxide solution, NaOH(aq) - in the solution

Question 17

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Answer 17

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