C3 Topic 3 - Electrolytic Process Flashcards
Define electrolyte.
A compound that ionises when dissolved or molten to make an electrically conductive medium.
Define electrolysis.
The decomposition of a compound produced in an electrolyte by an electric current.
Define anode.
A positively charged electrode.
Define cathode.
A negatively charged electrode.
Define oxidation.
A reaction in which atoms lose electrons.
Define reduction.
A reaction in which atoms gain electrons.
Define anion.
A negatively charged ion.
Define cation
A positively charged ion.
What happens in electrolysis of molten sodium chloride?
The sodium and the chloride are split up to form ions; Na+ and Cl-; which are then attracted to their oppositely charged electrodes, where they gain/lose electrons to make Na and Cl2.
Cathode:
Na+ + e- -> Na (reduction)
Anode:
2Cl- -> Cl2 + 2e- (oxidation)
What is different in electrolysis of a electrolytes in a solution compared with molten ones?
In a solution, the least reactive ion will be attracted to the electrodes as it is more ‘willing’ to be oxidised/reduced.
What happens in electrolysis of sodium chloride solution?
The sodium and the chloride are split up to form ions; Na+ and Cl-; as well as the water molecules; H+ and OH-. The least reactive are then attracted to their oppositely charged electrodes. Hydrogen ions are attracted to the cathode where they form hydrogen gas, while the chlorine ions go to the anode where the react to make chlorine gas.
Cathode:
2H+ + e- -> H2 (reduction)
Anode:
2Cl- -> Cl2 + 2e- (oxidation)
How can impure copper be purified through electrolysis?
The cathode used is a thin piece of pure copper, while the anode is a block of the impure copper to be purified. The electrolyte must have copper ions so copper sulphate, for example, could be used.
Once the electricity is supplied, the copper atoms are oxidised and lose two electrons, turning them into Cu2+ ions. The copper ions are then attracted to the cathode, where they gain two electrons and are turned back into copper atoms. Impurities from the anode sink as sludge.
Cathode:
Cu2+ + 2e- -> Cu
Anode:
Cu -> Cu2+ + 2e-
How would electroplating be used to coat a brass cup with silver?
Cathode: Brass cup
Anode: Silver bar
Electrolyte: Silver nitrate
After the power is turned on, the silver atoms are oxidised, turning them into positive ions which are attracted to the brass cup. Once there, they are reduced and coat the brass cup so that after the process is finished, there is a layer of silver covering the brass.
