LM P2 1i electrolysis Flashcards
what is electrolysis?
using electricity to convert the ions in a compound back into there pure elemental forms by the transfer of electrons
what is the equipment used in electrolysis?
- beaker, with electrolyte
- electrodes, made of metal or carbon
- cathode and anode (negative and positive)
- battery and wire to drive the process
what is the electrolyte?
liquid solution that contains an ionic compound, ions are free to move
how does electrolysis work?
the negative ions are attracted to the positive anode and the positive ions in the solution are attracted to the negative cathode
- the ions are discharged when it gets the the electrodes (become neutral atoms)
what do the ions do when they are at the electrodes?
get oxidised at the anode and reduced at the cathode
what the the electrons doing in electrolysis?
they get to the anode and are lost from the negative ions and then travel to the cathode (through the wire), they are then given to the positive ions.
what is an anion?
negative ions
what is a cation?
postive ions
what do you do to remove oxygen when the metal is less reactive than carbon
reduction with carbon, carbon will displace the oxygen to form pure metal and carbon dioxide
why is electrolysis expensive?
needs a lot of energy
how do you separate aluminium oxide into pure aluminium?
- purify bauxite into aluminium oxide
- melt aluminium oxide (mixed with cryolite) so it becomes molten
- set up equipment
- oxygen will be discharged at the anode and aluminium will gather at the cathode, and eventually fall to the bottom of the beaker to become molten aluminium
what is cryolite?
lowers the melting point of the metal oxide
what is OILRIG?
Oxidation Is Loss Reduction Is Gain
what is a cathode?
negative electrode that will attract positive ions
what is an anode?
positive electrode that will attract negative ions
what happens in electrolysis with an aqueous solution?
aqueous solutions also have hydrogen and hydroxide ions as well as the other ions.
- negative cathode will attract hydrogen and the metal ions, but will only discharge one ion
- the positive anode attracts the halide/or other element and the hydroxide
how do you know which ions is discharged on the cathode when doing electrolysis with an aqueous solution?
the ion of the least reactive will be discharged
how do you know which ions is discharged on the anode when doing electrolysis with an aqueous solution?
if the halide is present, the halide will get discharged
or if there isn’t a halide present, then its always the hydroxide that gets discharged
where does the metal go when doing electrolysis with an aqueous solution?
becomes and solid and accumulates around the cathode
what can be used as a calorimeter?
polystyrene drinking cup, a vacuum flask or a metal can
what is calorimetry?
technique used to measure changes in enthalpy of chemical reactions
- enthalpy changes of reactions in solution
- enthalpy changes of combustion
describes the reactions in solution experiment?
for dissolving, displacement and neutralisation
- fixed volume of one reagent is added to the calorimeter, initial temp is taken
- excess amount go the second reagent is added, stir continuously
- max temp is recorded and the temp rise is calculated
what things are assumes in reactions in?
- specific heat capacity and density of the solution is the same as pure water
- specific heat container is ignored
- complete reaction
- negligible heat losses
describes the combustion experiment?
- fixed volume of water is measured and transferred to a copper can
- spirit burner is weighted
- initial temp is measured and recorded
- burner is ignited, water is stirred
- when the temp has risen by about 20 degrees the flame is extinguish
- final temp recorded
sources of error in combustion?
- some heat is lost to surrounding, so not just water
- incomplete combustion
