C4 Electrolysis (pg 135) Flashcards
What is Elecrolysis?
It means ‘Splitting up with Electricity’
Electrolysis use an electrical current to cause a reaction.
What happens 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.
When positive ions in the electrolyte move, what do they move towards?
They move towards the cathode (-ve electrode) and gain electrons (they are reduced)
Where will the ‘negative ions’ in the electrolyte move towards?
they will move towards the anode (+ve electrode) and lose electrons (they are oxidised)
This creates a flow of charge through the electrolyte as ions travel to the electrodes.
What happens when ions gain or lose electrons?
they form the uncharged element and are discharged from the electrolyte.
What is an electrolye?
Its just a liquid or a solution that can conduct electricity.
What is a electrode?
it is a solid that conducts electricity and is submerged in the electrolyte.
What is a cathode?
the negatively charged electrode by which electrons enter an electrical device.
What is an anode?
the positively charged electrode by which the electrons leave an electrical device
What do oxidised mean?
undergo or cause to undergo a reaction in which electrons are lost to another species.
(iron (II) compounds are slowly oxidized by air to form iron (III) compounds
Electrolysis of Molten Ionic Solids forms what?
Elements
Why cant an ionic solid be electrolysed?
because the ions are in fixed positions and cant move.
Why can Molten ionic compounds be electrolysed?
because the ions can move freely and conduct electricity.
Molten ionic liquids, e.g. lead bromide, are always brokent up into their elements, how?
Positive metals ions are reduced to the element at the cathode:
Pb2+ + 2e- »_space;» Pb
Negative non-metal ions are oxidised to the element at the anode:
2Br- »_space;» Br2 + 2e-
Why should electrodes be inert? (not chemically reactive)
so they don’t react with the electroylte.
Metals can be extracted from their ores using what?
Electrolysis
When can electrolysis be used to extract metal?
If a metal is too reactive to be reduced with carbon (page 133) or reacts with carbon, then electrolysis can be used to extract it.
Extracting metals via this method is very expensive as lots of energh is required to melt the ore and produce the required current.
Aluminium is extracted from the ore bauxite by what?
electrolysis
Bauxite contains aluminium oxide, Al2O3
What is Bauxite?
Bauxites are rocks that contain minerals mostly from the group of aluminium hydroxide, mainly gibbsite (Al(OH)3), or aluminium oxide hydrate boehmite ALOOH) and rarel amorpous gel (Al(OH)3)
It is a white red, yellow or brown calylike substance comprising aluminium oxides and hydroxides often with such impurities as iron oxides. It is the chief ore of aluminium.
(an impure mixture of earthy hydrous aluminium oxides and hydroxides that is the principal source of aluminum
Aluminium oxide has a very high melting temperature, what is mixed to lower the melting point?
It gets mixed with cryolite to lower the melting point.
(cryolite is an aluminium based compound with a lower melting point than aluminium oxide)
A molten mixture contains free ions, what do this mean?
it will conduct electricity
What do molten mean?
fused or liquefied by heat. melted molten lava.
A positive Al3+ ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms….. what happens next?
These then sink to the bottom of the electrolysis tank.
The negative O2- ions are attracted to the positive electrode where they each lose two electrons. what happens next…..?
the neutral oxygen atoms will then combine to form O2 molecules.
(see diagram on page 135)
At the negative electrode, Metals form positive ions, so what are they attracted to?
negative electrode.
Non-metals form negative ions so they’re attracted to what?
positive electrode
Tell me the symbol equation for?
Aluminium oxide »_space;» aluminium + Oxygen
2Al2O3(l) »_space;»» 4Al(l) + 3O2(g)
A Student carried out electrolysis on molten calcium chloride. What is produced at:
a) the anode?
b) the cathode?
a) chlorine gas Cl2
b) Calcium atoms Ca
(it would be useful for your exams to learn the products of electrolysis of molten lead bromide)
What is the products of electrolysis of molten lead bromide, PbBr2(l)
Molten lead bromide, PbBr(l) is an electrolyte.
during electrolysis: Pb2+ ions gain electrons at the cathode and become Pb atoms.
Br- ions lose electrons at the anode and become Br atoms, which pair up to form Br2
(during the electrolysis of molten lead bromide, the bromide ions are converted to bromine atoms and the lead ions are converted to lead atoms)
