Electrolysis Flashcards
what is an electrolyte?
a liquid or solution that can conduct electricity
what is an electrode?
a solid that can conduct electricity and is submerged into the electrolyte (they should be inert so they don’t react with the electrolyte)
what happens during electrolysis?
1)During electrolysis, an electric current is passed through an electrolyte (a molten or dissolved ionic compound). The ions move towards the electrodes, where they react, and the compound decomposes.
2) The positive ions in the electrolyte will move towards the cathode (-ve electrode) and gain electrons (they are reduced).
3) The negative ions in the electrolyte will move towards the anode (+ve electrode) and lose electrons (they are oxidised).
4) This creates a flow of charge through the electrolyte as ions travel to the electrodes.
5) As ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte
what is the cathode?
The negatively charged electrode in electrolysis
what is the anode?
The positively charged electrode in electrolysis
why can’t an ionic solid be electrolysed?
they are in fixed positions and cannot move
why can molten ionic compounds be electrolysed?
their ions can move freely and conduct electricity
what happens to positive metal ions during electrolysis?
they are reduced to the element at the cathode
what happens to negative non metal ions during electrolysis?
they are oxidised to the element at the anode
when do we use electrolysis?
when a metal is too reactive to be reduced with carbon
what are the disadvantages of electrolysis?
it is very expensive as it requires a lot of energy to melt the ore and produce the required current
How is aluminium extracted by electrolysis?
1)Aluminium is extracted from the ore bauxite by electrolysis. Bauxite contains aluminium oxide
2) Aluminium oxide has a very high melting temperature so it’s mixed with cryolite(an aluminium based compound with a lower melting point than aluminium oxide) to lower the melting point.
3) The molten mixture contains free ions so it will conduct electricity(the molten mixture is used as the elctrolyte)
4) The positive Al3+ ions are attracted to the negative electrode (cathode)where they each pick up three electrons and turn into neutral aluminium atoms. These then sink to the bottom of the electrolysis tank.
5) The negative 02- ions are attracted to the positive electrode(annode) where they each lose two electrons. The neutral oxygen atoms will then combine to form O2 molecules.
7) the annode is made of carbon so needs to be replaced regularly as crabon reacts with oxygen to produce carbon dioxide
revise this pic of aluminium being extracted by electrolysis
introducing electrolysis video:
https://youtu.be/AhTRiL6xjBA
video on extracting aluminium:
https://youtu.be/YcyMElBEzAY
