2b.4 - Electroylsis

Question 1

What does oil rig stand for?

Answer 1

Oxidation Reduction
Is Is
Loss Gain

Question 2

What does oxidation involve?

Answer 2

Gain of oxygen or loss of electrons

Question 3

What does reduction involve?

Answer 3

Loss of oxygen or gain of electrons

Question 4

What does electrolysis always involve

Answer 4

Oxidation and reduction

Question 5

Explain what happens when lead bromide is electrolysed at the cathode? (2)

Answer 5

• The positive lead ions are attracted to the negative electrode. Here they are reduced (gain electrons).
• One lead ion accepts two electrons to become one lead atom

Question 6

What affects the products formed by electrolysis?

Answer 6

Reactivity

Question 7

How does reactivity affect electrolysis at the negative electrode? (2)

Answer 7

• If the metal ions and H+ ions are present, the metal ions will stay in the solution if they are more reactive than hydrogen.
• If the metal is less reactive than hydrogen, then the metal will be produced

Question 8

How does reactivity affect electrolysis at the positive electrode? (2)

Answer 8

• If OH- and halide ions are present then the molecules of chlorine, bromine, or iodine will be formed.
• If no halide ions are present, oxygen will be formed

Question 9

What products do you get in the electrolysis of sodium chloride?

Answer 9

Hydrogen, Chlorine, Sodium hydroxide

Question 10

What happens during the electrolysis of sodium chloride at the cathode? (2)

Answer 10

• Positive hydrogen ions are attracted to the negative electrode. Here they are reduced (gain electrons).
• Two hydrogen ions accept two electrons to become one hydrogen molecule

Question 11

What happens when lead bromide is electrolysed at the anode? (2)

Answer 11

• The negative bromide ions are attracted to the positive electrode.
• Here they are oxidised (lose electrons). Two bromine ions lose one electron each and become one bromine molecule

Question 12

What happens during the electrolysis of sodium chloride at the anode? (2)

Answer 12

• Negative chlorine ions are attracted to the positive electrode. Here they are oxidised (lose electrons)
• Two chloride ions lose their electrons and become one chlorine molecule

Question 13

Why do the sodium ions stay in the solution when sodium chloride is electrolysed?

Answer 13

It is more reactive than hydrogen

Question 14

Why is sodium hydroxide a product of the electrolysis of sodium chloride? (2)

Answer 14

• Sodium ions are more reactive than hydrogen so they are left behind
• Hydroxide ions are left from the water

Question 15

What are the half equations for the electrolysis of sodium chloride?

Answer 15

Positive: 2H+ + 2e- -> H2
Negative: 2Cl- -> Cl2 + 2e-

Question 16

What are the half equations for the electrolysis of molten lead bromide?

Answer 16

Positive : Pb2+ + 2e- -> Pb

Negative: 2Cl- -> Cl2 + 2e-

Question 17

How is electrolysis used to remove aluminium from its ore? (4)

Answer 17

• Al2O3 has a very high melting point (over 2000C, so would be very expensive to melt)
• Dissolved in molten cryolite to lower boiling point to 900C
• Electrodes made of graphite to conduct electricity
• Aluminium forms at the negative electrode and oxygen forms at the positive

Question 18

What ore is aluminium found in?

Answer 18

Bauxite

Question 19

Why does the positive electrode need to be replaced every now and again when used to remove aluminium from its core?

Answer 19

Because the oxygen that is produced on it reacts with the graphite to produce carbon dioxide

Question 20

What is electroplating used for?

Answer 20

To coat the surface of one metal with another metal

Question 21

What is at the positive and negative electrode when electroplating?

Answer 21

Negative - metal object

Positive - Pure metal you’re plating with

Question 22

What are the uses of electroplating? (2)

Answer 22

• Decoration

- Conduction