Electrolysis

Question 1

Define a cation and anion

Answer 1

A cation is a positively charged ion while an anion is negatively charged ion

Question 2

Define an electrode

Answer 2

An electrode is a metal or graphite rod by which the current enters of leaves an electrolyte

Question 3

Define an anode and electrode

Answer 3

Anode is a POSITIVE electrode that attracts anions (+ve battery terminal)
Cathode is a NEGATIVE electrode attracts cations (-ve battery terminal)

Question 4

What are electrolytic reactions

Answer 4

Oxidation happens at anode
OIL, Oxidation is loss of electrons
eg. 2Cl-(l) -> Cl2 (g) + 2e-

Reduction happens at cathode
RIG, Reduction is gain of electrons
2g. Na+(l) +e- -> Na (l)

Question 5

State Electrochemical series

Answer 5

Cations (Ca & Na) swapped with reactivity series)
K+
Ca2+
Na+
Mg2+
Al3+
Zn2+
Fe2+
Pb2+
H+
Cu2+
Ag+

Anions
F-
SO4 2-
NO3-
(F, SO4, NO3 not discharged from soln)
Cl-
Br-
I-
OH-

Question 6

What happens in a diluted aqueous soln?

Answer 6

Cathode (RIG)
2H+ +2e- -> H2 (g)

Anode (OIL)
4OH- -> 2H2O (l) +O2 (g) + 4e-

Question 7

product & pH change at cathode

Answer 7

2H+(aq) + 2e- -> H2 (g), colourless odourless gas produced (H2)
RIG
Hydrogen ions are discharged at cathode, solution at cathode turns alkaline as concentration of H+ ions decreases

Question 8

product and pH change at anode

Answer 8

4OH- (aq) -> 2H2O (l) + O2 (g) +4e-, colourless odourless gas, O2 produced
OIL
Hydroxide ions are discharged at cathode, solution turns acidic as concentration of OH- ions decreases

Question 9

What happens if both reactive electrodes are copper?

Answer 9

Copper cathode increases in size
RIG
Pink/reddish brown solid is formed
Copper formed

Copper anode decreases in size
OIL
effervescence
Cu2+ ions released

Question 10

Reaction with inert electrodes

Answer 10

CuSO4 with carbon electrodes

Cathode
Cu2+ (aq) + 2e- -> Cu (s)

Anode
4OH- (aq) -> O2(g) + 2H2O(l) + 4e-

Electrolyte becomes more acidic