ES.3 Flashcards
Electrolysis
How can chlorine be made to be used for bromine extraction?
Chlorine can be made industrially by electrolysis of concentrated solution of sodium chloride.
What is electrolysis?
It is the process of decomposing a compound using an electric current.
What are additional products (products other than the ones you want) called in a reaction?
Co-products.
What halogen is seaweed a source of?
Iodine.
What state must the compound be in for electrolysis to be possible and why?
It must molten or aqueous. This is because electrolysis requires free moving electrons to complete the circuit.
What are positively charged ions called?
Cation.
What are negatively charged ions called?
Anion.
What is the positive electrode called?
Anode (attracts anion).
What is the negative electrode called?
Cathode (attracts cation).
What happens at the positive electrode (anode)?
Anions lose electrons and are oxidised.
What happens at the negative electrode (cathode)?
Cations gain electrons and are reduced.
What are the electrodes normally made of?
Inert material like graphite.
What are the general products of electrolysis of molten salt?
Cathode: metal.
Anode: non-metal (apart from hydrogen).
Why do we electrolyse some compounds in aqueous form rather than molten?
Some salts have very high melting points so it’s very expansive to melt it.
Why could there be different unexpected products when electrolysising solutions?
Because the water in the solution will competes with the ions from the salt at electrodes.
What can happen to water at the cathode?
Water can be reduced to make hydrogen gas and hydroxide ions.
What can happen to water at the anode?
Water can be oxidised to make oxygen gas adn hydrogen ions.
What happpens at the cathode if the metal in the salt is from group 1 or 2 (reactive metal)?
Metal ions remain in the solution while hydrogen ions are reduced to form hydrogen gas.
What happens at the cathode if the metal in the salt is less reactive metal like copper and zinc?
The metal ions will be reduced and that metal will form at the cathode and hydrogen ions are left in the solution.
What happens at the anode if the salt contained halogen?
As halide ions have greater tendency to be oxidised than hydroxide ions, halide ions will be oxidised and halogen will be produced at the anode.
What happens at the anode if the salt contained nitrate or sulfate?
As nitrate and sulfate ions have less tendency to be oxidised than hydroxide ions, hydroxide ions will be oxidised and oxygen will be produced at the anode.
