Electrochemistry:
Redox reactions: Red = reduction, ox = oxidation
Electrolysis: Transfer of electrons
Redox reaction: Reaction involving the transfer of electrons
• Oxidation is the loss of electrons
OIL RIG : Oxidation is Loss, Reduction is Gain
• Reduction is the gain of electrons
• Oxidising agent: Substance that accepts (takes) electrons (Causes other species to lose electrons)
• Reducing agent: Substance that donates (gives) electrons (Causes other species to gain electrons)
Writing balanced equations using half reactions:
• A half reaction contains electrons:
- Either on the left of arrow (reduction)
- Or on the right of arrow (oxidation)
• Net reactions must NOT show any electrons
Li+ + e¡ ! Li Li ! Li+ + e¡
f
f
e on the left of e on the right of
arrow = reduction arrow = oxidation
reaction reaction
Electrolysis: Transfer of electrons
REDOX
!
!
reduction oxidation
1. Gaining of electrons 1. Loss of electrons
2. Reduction (decrease) in 2. Increase in
oxidation number oxidation number
, Electrolytic cells:
• Electrode reactions that are sustained by a supply of electrical energy (not spontaneous) (electrode
must be solid conductor: graphite/metal)
• Conversion of electrical energy into chemical energy
Processes and Redox reactions:
• Identify anode and cathode
Anode: Where oxidation takes place
Cathode: Where reduction takes place
• Write half reaction equations taking place at anode and cathode
• Write net ionic cell reaction (combine 2 half reactions)
• Identify oxidising and reducing agent for electrolytic reaction
• Identify or suggest suitable inert electrodes (don't react)
Electrolyte: A substance (liquid) that can conduct electricity by forming free ions when molten or
dissolved in solution
• Identify predominant half-reaction taking place at anode and cathode during electrolysis of
AQUEOUS solution
• Strongest RA or OA present in solution will be oxidised or reduced during electrolysis. Except
when their concentration becomes too low
• Role of concentration when predicting predominant anode half-reaction:
- When concentration of weak RA is HIGH, then it will undergo oxidation in preference to a strong
RA.
• Anode itself will be oxidised in preference to the ions:
- When electrode material is a stronger RA than ions in solution
- When graphite electrodes in Hall-Heroult cell react with oxygen
• Inherent reactivity (electrode potentials) will determine which half-reaction will be predominant at
Redox reactions: Red = reduction, ox = oxidation
Electrolysis: Transfer of electrons
Redox reaction: Reaction involving the transfer of electrons
• Oxidation is the loss of electrons
OIL RIG : Oxidation is Loss, Reduction is Gain
• Reduction is the gain of electrons
• Oxidising agent: Substance that accepts (takes) electrons (Causes other species to lose electrons)
• Reducing agent: Substance that donates (gives) electrons (Causes other species to gain electrons)
Writing balanced equations using half reactions:
• A half reaction contains electrons:
- Either on the left of arrow (reduction)
- Or on the right of arrow (oxidation)
• Net reactions must NOT show any electrons
Li+ + e¡ ! Li Li ! Li+ + e¡
f
f
e on the left of e on the right of
arrow = reduction arrow = oxidation
reaction reaction
Electrolysis: Transfer of electrons
REDOX
!
!
reduction oxidation
1. Gaining of electrons 1. Loss of electrons
2. Reduction (decrease) in 2. Increase in
oxidation number oxidation number
, Electrolytic cells:
• Electrode reactions that are sustained by a supply of electrical energy (not spontaneous) (electrode
must be solid conductor: graphite/metal)
• Conversion of electrical energy into chemical energy
Processes and Redox reactions:
• Identify anode and cathode
Anode: Where oxidation takes place
Cathode: Where reduction takes place
• Write half reaction equations taking place at anode and cathode
• Write net ionic cell reaction (combine 2 half reactions)
• Identify oxidising and reducing agent for electrolytic reaction
• Identify or suggest suitable inert electrodes (don't react)
Electrolyte: A substance (liquid) that can conduct electricity by forming free ions when molten or
dissolved in solution
• Identify predominant half-reaction taking place at anode and cathode during electrolysis of
AQUEOUS solution
• Strongest RA or OA present in solution will be oxidised or reduced during electrolysis. Except
when their concentration becomes too low
• Role of concentration when predicting predominant anode half-reaction:
- When concentration of weak RA is HIGH, then it will undergo oxidation in preference to a strong
RA.
• Anode itself will be oxidised in preference to the ions:
- When electrode material is a stronger RA than ions in solution
- When graphite electrodes in Hall-Heroult cell react with oxygen
• Inherent reactivity (electrode potentials) will determine which half-reaction will be predominant at
