Redox Reactions
Oxidation and Reduction
Oxidation: the loss of electrons. The substance which loses electrons is oxidised
Reduction: The gaining of electrons. The substance which gains electrons is reduced
- Represented by half reaction that show loss/gain of electrons
Example:
Reaction between Sodium and Chlorine
- Sodium donates electrons (e are on product side) and Chlorine gains (e are on reactant side)
- Oxidation: Na -> Na + e (multiply by 2 for nett so electrons =)
- Reduction: Cl + 2e -> 2Cl
- Nett: 2Na + Cl -> 2Na + 2Cl
Oxidising and reducing agents
Reducing agent: a substance which donates electrons and thus causes the reduction of another substance
- The reducing agent itself is oxidised
Oxidizing agent: A substance which accepts electrons and thus causes the oxidation of another substance
- The oxidising agent itself is reduced
Electrolytic Cells
- Electricity flows through molten salt or a solution containing ions (electrolyte) & the ions undergo a
chemical reaction
- Aka: electrolysis and it takes place in an electrolytic cell
- Non-spontaneous reactions
- Electrical to chemical energy
- Electrolytic cell contains two inert cells connected to a DC supply and dipped into the electrolyte
- Electrons flow from the negative terminal to an electrode, then current is carried by ions, to the
second electrode then back to the positive terminal. During this ions undergo a CR
Competition
- In solutions only
- Water can also be reduced/oxidised at the cathode/anode
- Anode: unless there is a halogen (Cl ,Br ,I etc) water reacts
- Cathode: The stronger oxidising agent between the ion and water will be reduced
, The electrolysis of copper chloride
- When dissolved in water produces a blue solution because of Cu ions
- CuCl -(H20)-> Cu + 2Cl
Copper:
- When electrodes are dipped into solutions, Cu ions move to negative electrode
- Half-reaction: Cu + 2e -> Cu
- Electrons are gained therefore reduction occurs at the Cathode
- Blue lessens as Cu concentration decreases & Cu layer forms at cathode
Chlorine:
- Move towards positive electrode as they lose electrons
- Half-reaction: 2Cl → Cl + 2e
- Electrons are lost therefore oxidation occurs at the anode
- Chlorine gas is produced at the anode
Net:
- CuCl -> Cu + Cl
- Copper chloride is decomposed by electrolysis
NOTES:
OIL RIG - Oxidation is Loss & Reduction is gain
PANIC - Positive Anode Negative Cathode (i is for ions only) - does not work for galvanic
Industrial Applications
Electroplating
- One metal is coated with another (taps eg)
- Makes them attractive and prevents rusting or scratching
- Item being plated is the cathode & anode is a bar of metal which is doing the coating
- The electrolyte contains ions of the metal
Chromium plating example
- Reduction (Anode): Cr + 3e -> Cr
- Oxidation (Cathode): Cr -> Cr + 3e
- Nett: Cr + Cr -> Cr + Cr (balance in solution)
Oxidation and Reduction
Oxidation: the loss of electrons. The substance which loses electrons is oxidised
Reduction: The gaining of electrons. The substance which gains electrons is reduced
- Represented by half reaction that show loss/gain of electrons
Example:
Reaction between Sodium and Chlorine
- Sodium donates electrons (e are on product side) and Chlorine gains (e are on reactant side)
- Oxidation: Na -> Na + e (multiply by 2 for nett so electrons =)
- Reduction: Cl + 2e -> 2Cl
- Nett: 2Na + Cl -> 2Na + 2Cl
Oxidising and reducing agents
Reducing agent: a substance which donates electrons and thus causes the reduction of another substance
- The reducing agent itself is oxidised
Oxidizing agent: A substance which accepts electrons and thus causes the oxidation of another substance
- The oxidising agent itself is reduced
Electrolytic Cells
- Electricity flows through molten salt or a solution containing ions (electrolyte) & the ions undergo a
chemical reaction
- Aka: electrolysis and it takes place in an electrolytic cell
- Non-spontaneous reactions
- Electrical to chemical energy
- Electrolytic cell contains two inert cells connected to a DC supply and dipped into the electrolyte
- Electrons flow from the negative terminal to an electrode, then current is carried by ions, to the
second electrode then back to the positive terminal. During this ions undergo a CR
Competition
- In solutions only
- Water can also be reduced/oxidised at the cathode/anode
- Anode: unless there is a halogen (Cl ,Br ,I etc) water reacts
- Cathode: The stronger oxidising agent between the ion and water will be reduced
, The electrolysis of copper chloride
- When dissolved in water produces a blue solution because of Cu ions
- CuCl -(H20)-> Cu + 2Cl
Copper:
- When electrodes are dipped into solutions, Cu ions move to negative electrode
- Half-reaction: Cu + 2e -> Cu
- Electrons are gained therefore reduction occurs at the Cathode
- Blue lessens as Cu concentration decreases & Cu layer forms at cathode
Chlorine:
- Move towards positive electrode as they lose electrons
- Half-reaction: 2Cl → Cl + 2e
- Electrons are lost therefore oxidation occurs at the anode
- Chlorine gas is produced at the anode
Net:
- CuCl -> Cu + Cl
- Copper chloride is decomposed by electrolysis
NOTES:
OIL RIG - Oxidation is Loss & Reduction is gain
PANIC - Positive Anode Negative Cathode (i is for ions only) - does not work for galvanic
Industrial Applications
Electroplating
- One metal is coated with another (taps eg)
- Makes them attractive and prevents rusting or scratching
- Item being plated is the cathode & anode is a bar of metal which is doing the coating
- The electrolyte contains ions of the metal
Chromium plating example
- Reduction (Anode): Cr + 3e -> Cr
- Oxidation (Cathode): Cr -> Cr + 3e
- Nett: Cr + Cr -> Cr + Cr (balance in solution)
