Electrolysis

what happens at anode - Electrolysis of molten Lead Bromide

• 2Br^- → Br₂ + 2e^-

• oxidation

• bromide ions have been oxidised

what happens at cathode - Electrolysis of molten Lead Bromide

(negative)

• Pb2+ + 2e- → Pb

• reduction

what is given off at anode - Electrolysis of molten Lead Bromide

Bromine gas (orange)

what accumulates at cathode - Electrolysis of molten Lead Bromide

molten lead

what is electrolyte?

ionic substance (melted/in solution split by electrolysis

what are electrodes made out of, why?

• made of graphite

• inert so doesn’t interact with reaction

what are the two rules - electrolysis of solutions

Now we have H₂O → splits to give H⁺ (cathode) and OH^- (anode) ions

1. CATHODE

   • competition between metal ion + hydrogen ion

   • MOST reactive STAYS in solution

2. ANODE

   • is there a halide/group 7 ion

   • yes → that halogen is formed

   • no → oxygen is formed

half equation for formation of oxygen at anode

4OH^- → O₂ + 2H₂O + 4e^-

CuSO4 electrolysis anode/cathode

Anode - bubbles of gas, oxygen formed

cathode - pink/brown solid coating, copper formed

H₂SO₄ electrolysis anode/cathode

anode - bubbles of gas, oxygen formed

cathode - bubbles of gas, hydrogen formed

NaCl

anode - bubbles of gas, chlorine formed

cathode - bubbles of gas, hydrogen formed

electrolysis - why should circuit not be connected for more than a few minutes

they may produce toxic gas e.g. chlorine

why is there a light in the electrolysis circuit

to ensure it is working

why are copper, sodium and hydrogen ions attracted to the cathode?

they are positive ions and the cathode is negative - opposite charges attract

where does the H+ and the OH- come from in the experiment

the solution that is being tested - water splits into the ions