SC10 - Electrolysis ✓

Question 1

SC10a - Define electrolysis

Answer 1

The process in which energy transferred by a d.c current decomposes electrolytes

Question 2

SC10a - Describe the relationship between positive and negative ions and their electrode, naming them.

Answer 2

• (Positive) Cations are attracted to the (negative) Cathode
• (Negative) Anions are attracted to the (positive) Anode

Question 3

SC10a - Why is an electrolyte able to conduct electricity?

Answer 3

• When an ionic solid is melted down or dissolved in water, its ionic bonds breaking meaning that the ions inside are now free to move.
• This allows the electrolyte to conduct electricity.

Question 4

SC10a - Describe the setup for an electrolysis exmperiment.

Answer 4

• Two electrodes (cathode and anode) are connected to a d.c supply.
• They are also placed in the electrolyte (which is either molten or aqueous).

Question 5

SC10a - At which electrodes do oxidation and reduction take place and how do these processes affect ions?

Answer 5

• Oxidation is the loss of electrons and takes place at the anode. Reduction is the gain of electrons and takes place at the cathode.
• OIL RIG:
• Oxidation Is Loss;
• Reduction Is Gain

Question 6

SC10a - Use half equations to display the oxidation and reduction of Zinc and Chlorine during electrolysis.

Answer 6

Zn²⁺ + 2e^- → Zn (Reduction)

2Cl^- → Cl² + 2e^- (Oxidation)

Question 7

SC10a CP - Descirbe what you would expect to see when conducting the electrolysis of copper chloride solution using graphite (inert) electrodes.

Answer 7

• The cathode will be coated with a brownish layer.
• This shows copper is being produced
• At the anode there will be bubbles.
• This indicates that a gas is being produced
• If you hold a damp blue litmus paper near this, it will turn red and then bleach white.
• This indicates that the gas produced is chlorine

Question 8

SC10a CP - Describe how pure copper is obtained through the electrolysis of copper sulfate solution using copper electrodes.

Answer 8

• Anode - Impure Copper
• Cathode - Pure Copper
• Solution - Copper Sulfate

Cu2+ ions from the anode move to the cathode, where they are deposited as copper ions. Impurities form as slude below the anode.

Question 9

SC10b - How can you predict the products of electrolysis?

Answer 9

• When electrolysing a solution, water will always be present
• This means H⁺ and OH^- ions are always present
• At the cathode, the metal can only be produced if it is less reactive than H⁺
• At the anode Oxygen will always be produced unelss the negative ion is a halide (has a charge of 1^-)
• If the electrolyte is molten, the components of the electrolyte will be produced

Question 10

SC10b - Give the half equation for the oxidation of a Hydroxide Ion

Answer 10

4OH^- -> O₂ + 2H₂0 + 4e^-

Question 11

SC10b - Describe the tests for chlorine gas

Answer 11

• Chlorine wll turn a damp blue litmus paper red, then will bleach it white

Question 12

SC10b - How do we test for oxygen gas?

Answer 12

• We hold a glowing splint to the gas - if it’s oxygen, the splint will reignite since oxygen supports combustion

Question 13

SC10b - Explain why the electrolysis of acidified water produces 2x as much hydrogen as oxygen

Answer 13

In the formula H₂0, there is 2 hydrogens for every oxygen