electrolysis

Question 1

what are electrolytes (definition)

Answer 1

ionic compounds in then molten state or dissolved in water

Question 2

describe/define electrolysis

Answer 2

a process in which electrical energy (from a direct current supply) decomposes electrolytes

Question 3

describe the movement of cations during electrolysis

Answer 3

cations (positively charged) migrate to the negatively charged cathode (opposites attract)

Question 4

describe the movement of anions during electrolysis

Answer 4

anions (negatively charged) migrate to the positively charged anode (opposites attract)

Question 5

what would be formed during electrolysis of molten copper chloride (inert electrodes)

Answer 5

cathode - copper
anode - chlorine

Question 6

what would be formed during electrolysis of molten lead bromide (inert electrodes)

Answer 6

cathode - lead
anode - bromine

Question 7

what state are the halides at room temp

Answer 7

chlorine - gas
bromine - liquid
iodine - solid

Question 8

what is oxidation in terms of electrons

Answer 8

oxidation is the loss of or act of losing electrons

Question 9

what is reduction in terms of electrons

Answer 9

reduction is the gain or act of gaining electrons

Question 10

what does O.I.L.R.I.G stand for

Answer 10

oxidation. is. loss. reduction. is. gain

Question 11

what reaction (redox) occurs at the cathode

Answer 11

reduction

Question 12

what reaction (redox) occurs at the anode

Answer 12

oxidation

Question 13

how do hydrogen-oxygen fuel cells work

Answer 13

use hydrogen and oxygen to produce a voltage, only product is water

Question 14

when/why do chemical cells run out

Answer 14

produces a voltage until one of the reactants is used up
in a rechargeable chemical cell, the reaction can essentially be reversed but eventually it will run out for good

Question 15

advantages of fuel cells [4]

Answer 15

as long as fuel can be provided, a voltage can be made in the cell so it doesn’t run out
only by-product when being used is water so no harmful emissions from usage
hydrogen is a widely available gas

Question 16

disadvantages of fuel cells [4]

Answer 16

releases carbon dioxide into the atmosphere when hydrogen is extracted from fossil fuels or natural gases so the whole process is not green expensive
hydrogen is hard to store (and flammable)

Question 17

half equation at the cathode of copper

Answer 17

Cu^2+ + 2e^- -> Cu

Question 18

half equation at the anode of bromine

Answer 18

2Br^- -> Br2 + 2e^-

Question 19

half equation at the anode of hydroxide

Answer 19

4OH^- -> 2H2O + 4e^- + O2

Question 20

what product is formed at the cathode in solution

Answer 20

either H^+ or the metal cation is formed. the one which is least reactive is formed

Question 21

what product is formed at the anode in solution

Answer 21

either OH^- (which then forms oxygen) or the non-metal anion is formed. the non-metal anion is only formed if the non-metal anion is a halide

Question 22

inert meaning

Answer 22

unreactive

Question 23

how would you electroplate a spoon with silver

Answer 23

replace the cathode with a copper spoon and replace the anode with silver and the solution would be silver nitrate this way at the anode silver ions in solution will be created and then at the cathode these ions would reform a solid layer of silver around the copper spoon -> electroplating

Question 24

how would you purify a piece of unpure copper with electrolysis

Answer 24

replace the anode with impure copper and the copper would go via solution to the cathode where we would have pure copper being deposited. the impurities fall out of the impure anode because they are not being oxidised and fall to the base to form a sludge. copper is below silver on the reactivity series so therefore copper is easier to oxidise than silver.

Question 25

how does copper move through the solution in electrolysis of solution CuSO4 with copper electrodes

Answer 25

Cu(s) —> (Cu2+) —> Cu(s)
anode -> (solution) -> cathode

Question 26

how does the concentration of copper ions as electrolysis progresses (copper electrodes, solution CuSO4)

Answer 26

stays the same because at the anode Cu(s) ions in solution are being into from Cu2+ while at the cathode Cu2+ are being turned into Cu(s) so it balances out

Question 27

potential species for oxidation (anode) in electrolysis of solution CuSO4 with copper electrodes

Answer 27

could either be the normal options; SO4^2- or OH^-, OR the copper from the electrode could react (it depends on which is less reactive and whether one of the options is a halide)

Question 28

what is the difference between electrolysis of solutions with inert electrodes, vs with metal electrodes

Answer 28

when we use metal electrodes, we have to consider the possibility that the metal could react

Question 29

potential species for oxidation (cathode) in electrolysis of solution CuSO4 with copper electrodes

Answer 29

could either be the normal options of Cu^2+ (from the solution) or H^+ OR it could be the metal ions from the electrode. it depends on which is least reactive

Question 30

mass change of anode (copper electrodes)

Answer 30

decreasing

Question 31

mass change of anode (copper electrodes)

Answer 31

increasing