Chemistry - electrolysis (chemical changes)

what happens to an ionic compound if it is molten?

the ions are free to move (delocalised) and can then conduct electricity

electrolytes

ionic compound that is molten or dissolved in water

electrolysis

decomposition of an ionic liquid by the passing of an electric current through it

cathode

the negative electrode, positive ions move here

anode

the positive electrode, negative ions move here

electrode

an electrical conductor that is places in electrolyte

why are metals mostly produced at the cathode?

metals are positive ions, cathode attracts positive ions as it is negative (opposites attract)

cations

positively charged ions

anions

negatively charged ions

oxidation

occurs at the positive electrode, where negative ions lose electrons

reduction

occurs at the negative electrode, where positive ions gain electrons

what can be produced at the cathode?

• metals are produced if the metal is less reactive than hydrogen

• hydrogen can be produced if the metal is more reactive than hydrogen

why are inert electrodes used during electrolysis?

so that it doesn’t react with the electrolyte or products

what can be produced at the anode?

• oxygen is produced

• if the solution has halide ions (chloride, bromide, iodide) then the halogen (chlorine, bromine, iodine) is produced

what is cryolite and why is it used?

aluminium oxide which is dissolved in cryolite to lower its melting point to save money on energy costs

explain why the positive electrode must be continually replaced

it wears away as the graphite (carbon) reacts with oxygen to form carbon dioxide

OILRIG

oxidation is loss reduction is gain

half equation for oxidation

element/ ion → ionⁿ⁺ + ne⁻

half equation for reduction

ionⁿ⁺+ ne⁻ → element

half equation for ionisation of water

H₂O_(l) → H⁺_(aq) + OH^-_(aq)