Electrolysis

Question 1

What is an electrolyte?

Answer 1

• An ionic compound in its molten or aqueous state.
• Aqueous - dissolved in water.

Question 2

Why can an electrolyte carry charge?

Answer 2

An ionic compound in is molten or aqueous state has mobile ions which can carry charge.

Question 3

What is electrolysis?

Answer 3

A process which uses electrical energy (from a direct current supply) to decompose electrolytes.

Question 4

What is the cathode and anode?

Answer 4

• Cathode - negative electrode
• Anode - positive electrode

Question 5

Where do charged ions in the electrolyte move to during electrolysis?

Answer 5

• Cations (positive ions) move towards the cathode (negative electrode).
• Anions (negative ions) move towards the anode (positive electrode).

Question 6

What happens at the anode during electrolysis?

Answer 6

The anions (negatively charged ions) lose electrons to form their elements.

Question 7

What happens at the cathode during electrolysis?

Answer 7

Cations (positively charged ions) gain electrons to form their elements.

Question 8

Name the processes that occur at each electrode during electrolysis

Answer 8

• Anode (positive) - oxidation
• Cathode (negative) - reduction.

Question 9

What is formed at each electrode in electrolysis?

Answer 9

• Positive electrode: Non metal
• Negative electrode: Metal or hydrogen

Question 10

How can you predict whether a metal or hydrogen will form at the negative electrode?

Answer 10

If hydrogen is above the metal in the reactivity series then the metal will form. If the metal is more reactive than hydrogen then hydrogen will form.

Question 11

What is formed at each electrode during the electrolysis of copper chloride solution?

Answer 11

• Positive electrode: Chlorine
• Negative electrode: Copper

Question 12

What is formed at each electrode during the electrolysis of sodium sulfate solution?

Answer 12

• Positive electrode: Oxygen
• Negative electrode: Hydrogen

Question 13

What is formed at each electrode during the electrolysis of molten lead bromide?

Answer 13

• Positive electrode: Bromine
• Negative electrode: Hydrogen

Question 14

Predict what will be formed at each electrode during the electrolysis of molten zinc chloride

Answer 14

• Positive electrode: Chlorine
• Negative electrode: Zinc

Question 15

What is formed at each electrode during the electrolysis of sodium chloride solution?

Answer 15

• Positive electrode: Chlorine
• Negative electrode: Hydrogen

Question 16

What is formed at each electrode during the electrolysis of water acidified with sulfuric acid?

Answer 16

• Positive electrode: Oxygen
• Negative electrode: Hydrogen

Question 17

What are the half equations for the reactions occuring at the cathode and anode during the electrolysis of copper chloride?

Answer 17

• Anode: 2Cl^- → Cl₂ + 2e^-
• Cathode: Cu²⁺+ 2e^- → Cu

Question 18

What does oxidation mean in terms of electrons?

Answer 18

Loss of electrons

Question 19

What does reduction mean in terms of electrons?

Answer 19

Gain of electrons

Question 20

Describe how electrolysis of copper sulfate can be used to purify copper

Answer 20

• Place 2 copper electrodes into copper sulfate solution. The anode should be impure copper and cathode should be pure copper. Connect to a power supply.
• The copper in the impure anode is pulled towards the cathode to form pure copper. Impurities form as sludge below the anode. Cu2+ ions from copper sulfate remain in solution.