Electrolysis

Question 1

What is electrolysis?

Answer 1

The breaking down of a compound using electricity

Question 2

Name of positive electrode

Answer 2

Anode ( as it attracts NEGATIVE anions)

Question 3

Name of negative electrode

Answer 3

Cathode ( as it attracts POSITIVE cations)

Question 4

What are electrodes usually made from

Answer 4

• Graphite (cheap)
• Platinum (expensive)

Question 5

requirements for an electrode

Answer 5

• must be a solid that is conductive but inert (unreactive)

Question 6

what is the electrolyte?

Answer 6

the substance to be broken down
-must conduct electricity

Question 7

Why must the electrolyte be a molten or dissolved ionic compound or a metal?

Answer 7

• needs charged particles that are free to move
• ionic compounds have charged particles, but they are not free to come in a solid

Question 8

why do covalent compounds not work for electrolysis

Answer 8

Do not have charged particles

Question 9

Anomaly of covalent compound that can work in electrolysis

Answer 9

ammonia

Question 10

What happens at anode in electrolysis of molten ionic compound?

Answer 10

non-metal ions lose electrons to form molecules (oxidised)

Question 11

Half equation of electrolysis of molten MgCl2 (anode)

Answer 11

2Cl- -> Cl2 + 2e-

Question 12

Half equation of electrolysis of molten MgCl2 (cathode)

Answer 12

Mg2+ + 2e- —> Mg

Question 13

What happens at cathode in electrolysis of molten ionic compound?

Answer 13

metal ions gain electrons to form atoms (reduced)

Question 14

observations at cathode

Answer 14

• solid (metal) formed

Question 15

observations at anode

Answer 15

-effervescence due to gas formed
-(may be liquid in aqueous electrolysis as heat not required)

Question 16

what happens to ions in water? (aqueous electrolysis)

Answer 16

water molecules can break apart (disassociate) and form H+ and OH- ions

Question 17

Complications of aqueous electrolysis

Answer 17

• now 4 types of ion rather than 2 ( 2 positive, 2 negative), so must work out which is attracted to electrode and which remains in solution

Question 18

How to decide which ion reacts at anode ( aqueous electrolysis)

Answer 18

• If halide ion ( Cl-/Br-/I-) is present, element is produced as normal at electrode
• otherwise O2 and H2O are produced

Question 19

formula for O2 and H2O production at anode (aqueous electrolysis)

Answer 19

4OH- –> O2 + 2H20 + 4e-

Question 20

how to decide which ion reacts at cathode ( aqueous electrolysis)

Answer 20

-If metal less reactive than Hydrogen, element produced as normal at electrode (gold, silver, copper)
- Otherwise, Hydrogen produced

Question 21

formula for Hydrogen production at Cathode (aqueous electrolysis)

Answer 21

2H+ + 2e- —> H2