LM P2 1i electrolysis

Question 1

what is electrolysis?

Answer 1

using electricity to convert the ions in a compound back into there pure elemental forms by the transfer of electrons

Question 2

what is the equipment used in electrolysis?

Answer 2

• beaker, with electrolyte
• electrodes, made of metal or carbon
  
  • cathode and anode (negative and positive)
• battery and wire to drive the process

Question 3

what is the electrolyte?

Answer 3

liquid solution that contains an ionic compound, ions are free to move

Question 4

how does electrolysis work?

Answer 4

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)

Question 5

what do the ions do when they are at the electrodes?

Answer 5

get oxidised at the anode and reduced at the cathode

Question 6

what the the electrons doing in electrolysis?

Answer 6

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.

Question 7

what is an anion?

Answer 7

negative ions

Question 8

what is a cation?

Answer 8

postive ions

Question 9

what do you do to remove oxygen when the metal is less reactive than carbon

Answer 9

reduction with carbon, carbon will displace the oxygen to form pure metal and carbon dioxide

Question 10

why is electrolysis expensive?

Answer 10

needs a lot of energy

Question 11

how do you separate aluminium oxide into pure aluminium?

Answer 11

1. purify bauxite into aluminium oxide
2. melt aluminium oxide (mixed with cryolite) so it becomes molten
3. set up equipment
4. 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

Question 12

what is cryolite?

Answer 12

lowers the melting point of the metal oxide

Question 13

what is OILRIG?

Answer 13

Oxidation 
Is 
Loss
Reduction 
Is 
Gain

Question 14

what is a cathode?

Answer 14

negative electrode that will attract positive ions

Question 15

what is an anode?

Answer 15

positive electrode that will attract negative ions

Question 16

what happens in electrolysis with an aqueous solution?

Answer 16

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

Question 17

how do you know which ions is discharged on the cathode when doing electrolysis with an aqueous solution?

Answer 17

the ion of the least reactive will be discharged

Question 18

how do you know which ions is discharged on the anode when doing electrolysis with an aqueous solution?

Answer 18

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

Question 19

where does the metal go when doing electrolysis with an aqueous solution?

Answer 19

becomes and solid and accumulates around the cathode

Question 20

what can be used as a calorimeter?

Answer 20

polystyrene drinking cup, a vacuum flask or a metal can

Question 21

what is calorimetry?

Answer 21

technique used to measure changes in enthalpy of chemical reactions

• enthalpy changes of reactions in solution
• enthalpy changes of combustion

Question 22

describes the reactions in solution experiment?

Answer 22

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

Question 23

what things are assumes in reactions in?

Answer 23

• specific heat capacity and density of the solution is the same as pure water
• specific heat container is ignored
• complete reaction
• negligible heat losses

Question 24

describes the combustion experiment?

Answer 24

• 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

Question 25

sources of error in combustion?

Answer 25

• some heat is lost to surrounding, so not just water

- incomplete combustion