Electrolysis

Question 1

Electrolysis

Answer 1

The breaking down of a molten or aqueous ionic compound using electricity

Question 2

Electrolysis of molten iconic compounds (eg. PbBr2 —> Pb + Br2)

Answer 2

ANODE - negative bromide ions are attracted to the positive anode where they loose electrons, forming bromine (2Br^- —> Br2 + 2e^-) OXIDATION
CATHODE - positive lead ions are attracted to the negative cathode where they gain electrons, forming lead (Pb^2+ + 2e^- —> Pb) REDUCTION

Question 3

Electrolysis of aqueous salts rules

Answer 3

H+ and OH- ions are present
Element formed at the anode = halogen>hydroxide>other
Element formed at the cathode = least reactive>

Question 4

Electrolysis of aqueous salts examples

Answer 4

NaCl
-ANODE (Cl- and OH- ions are attracted, Cl2 is formed)
-CATHODE (Na+ and H+ are attracted, H2 is formed)

H2SO4
-ANODE (SO4^2- and OH- ions are attracted, O2 (+a bit of H20) is formed)
-CATHODE (H+ and H+ ions are attracted, H2 is formed)

Question 5

Electrolysis using inert electrodes

Answer 5

ANODE - negative ions loose electrons and become elements (OXIDISED)
CATHODE - positive ions gain electrons and become elements (REDUCED)

Question 6

Electrolysis using non-inert electrodes

Answer 6

ANODE - metal atoms loose electrons and form positive ions (OXIDISED)
CATHODE - positive ions gain electrons and become elements (REDUCED)

Question 7

Electroplating

Answer 7

The use of electricity to cover one metal with another

Question 8

Using copper electrodes practical

Answer 8

1) select two clean pieces of copper foil, label one anode and the other cathode
2) measure and record the masses of each electrode using a balance
3) turn on the power and adjust the variable resistor to give a current of 0.2A
4) after 20 minutes, turn the power off, remove the electrodes and wash them with distilled water
5) dip them in propanone and gently shake off
6) measure and record the masses of the dry electrodes
7) repeat with different currents