electrolysis Flashcards
what is meant by electrolysis
the breakdown of substances (electrolyte) using electricity
why are the electrodes usually inert/ unreactive
so they dont react w the elctrolysis product or the electrolyte
why can ionic compounds only be electrolysed when theyre molten or dissolved in water
cause their ions are free to move around and carry diff chargers to the eletrode
whats the charge of an anode
positive electrode
whats an cathode
negative electrode
what happens at the cathode
positively charged ions gain electrons to become stable elements
what happens at the anode
negitvely charged ions loose electrons to become stable elements
how can reactions at the electrodes be represented
half equations
what happens in electolysis of aqeous solutions
in cathode-less reactuve element (metal or hydrogen) is displaced and the more reactive one is left in the solution
in anode- hydroxide ions are discharged unless a halide ion is pressent
whatre the steps of extracying aluminium
baxuxite is purified -> aluminium oxide is electrolysed to form aluminium and oxygen
whatre the steps to electrolyse aluminium oxide
1- molten aluminium oxide is mixed with cryolite to lower its melting point so less energy is needed
2- carbon electrodes need to be regularly replaced or they burn away
3-aluminium is formed in the cathode and oxygen formed in anode
what happens in the anode and cathode in the elctrolysis of aluminium oxide
cathode- aluminium is reduced (gains 3 electrons)
to form Al atoms
anode- oxygen is oxidised (loses 2 electrons) then reacts with the carbon anode to form carbon dioxide gas
What is the name of the substance that is mixed with aluminium oxide to lower its melting point?
cryolite
whatre the 3 products you get from electrolysising concentrated sodium chloride (brine)
sodium hydroxide,chlorine and hydrogen
what happens in the anode cathode and rest of solution in brine
anode- chlorine is oxidised (loses an electron)
cathode- hydrogen displaces sodium and is reduced to (gains 2 electrons)
sodium and hydroxide ions left in the solution react to form sodium hydroxide
whatre the uses of hydrogen,chlorine and sodium hydroxide
hydrogen can be used to make margirine
sodium hydroxide used to make paper and bleach and soap
chlorine used to make bleack to disinfect bacteria and plastics
where are metals usually formed
at the cathode
whats meant by electroplating
coating an object with a metal layer by electrolysis
why do we electroplate
- to protect metal from scratches nd corroding
- to preserve and use less amts of expensive and rare metals
- to increase attractiveness
how do we electroplate
- use plated object at cathode
-use plating metal as anode
-use ions of plating metal in electrolyte
what happens when you electolyse copper sulfate
-the cathode gains mass (metals formed) and the anode loses the same mass the cathode gains
loss of mass in anode when using active electrode =..
gain of mass in cathode
what happens when carbon electrodes are used in copper sulfate
copper is still deposited at cathode
oxygen is given off in anode from the hydroxide ions in electolyte
