Lesson 6: Electrolysis

Question 1

What is electrolysis?

Answer 1

• Electrolysis is the separation of an ionic compound by electricity.

Question 2

What type of solutions does electrolysis occur in?

Answer 2

• Aqueous
• Molten
• as ions can move to anode/ cathode

Question 3

What is an electrolyte?

Answer 3

• The molten/ dissolved ionic compounds.

Question 4

Where do the positive ions move to?

Answer 4

• Negative electrode
• Known as cathode.

Question 5

Where do negative ions move to?

Answer 5

• Positive electrode
• Known as anode

Question 6

What happens to ions at either electrode?

Answer 6

• Ions are discharged, producing elements.

Question 7

Why does electrolysis take a large amount of energy?

Answer 7

1.) To melt the compounds
2.) To produce the electric current.

Question 8

Are ions oxidised/ reduced at negative electrode?

Answer 8

• Reduced
• They gain electrons

Question 9

Are ions oxidised/ reduced at positive electrode?

Answer 9

• Oxidised
• They lose electrons.

Question 10

What are the electrodes used in aluminium oxide extraction made from?
Why?

Answer 10

• Carbon (specifically graphite)
• Good conductor of electricity.

Question 11

What is added to aluminium oxide to the lower the melting point of it to make it molten?

Answer 11

• Cryolite

Question 12

Why does the positive electrode have to be continually replaced when using graphite electrodes with aluminium oxide?

Answer 12

• The oxygen reacts with carbon (electrod), forming carbon dioxide at anode.
• So, carbon has been wearing out

Question 13

When is hydrogen produced at the negative electrode?

Answer 13

• If metal is more reactive than hydrogen, hydrogen will be produced at negative electrode.

Question 14

What is formed at positive electrode?
What is the exception?

Answer 14

• Oxygen
• Unless it contains halide ions, halogen is produced then.

Question 15

Other than electrolysis of aluminium oxide, what are the electrodes made from normally and why?

Answer 15

• Platinium
• To be inert
• Doesn’t react with elements formed.
• Some other are made of graphite (but graphite is inert in that case.)

Question 16

What is formed at the positive electrode if there are no halide ions in solution?
How does this happen?

Answer 16

• Oxygen formed
• Hydroxide ions move to positive electrode, form water and oxygen at the electrode.

Question 17

What is the half equation for the hydrogen ion at the negative electrode?

Answer 17

2H⁺+2e⁻ –> H₂

Question 18

What is the half equation for the hydroxide ion at the positive electrode?

Answer 18

4OH⁻ —> O₂ + 2H₂O + 4e⁻

Question 19

What are the steps of the electrolysis of copper II chloride and sodium chloride?

Answer 19

1.) Pour solution into beaker
2.) Place plastic petri dish with holes over beaker.
3.) Put carbon, graphite rods into the beaker
4.) Attach electrodes to crocodile clips and then power supply.
5.) Switch on P.D of 4V
6.) Observe products formed
(no longer than 5 minutes)
TESTS:
Damp, blue litmus paper –> bleached (chlorine.)
Collect Hydrogen –> squeaky pop sound.

Question 20

What is safety precaution from electrolysis of aqueous solutions practical?

Answer 20

• Switch off power supply after 5 minutes.
• Too much chlorine produced.
• Wear eye protection at all times

Question 21

Why is graphite inert in some cases but not in all?
What are those cases?

Answer 21

• When oxygen is produced, carbon will react with oxygen forming carbon dioxide.
• When oxygen isn’t produced, nothing will react with the carbon at the anode.

Question 22

If there is no halide ion, which ion is actually moving to the positive electrode?
What does this ion form?

Answer 22

• OH⁻
• Forms O₂ + H₂O