electrolysis

Question 1

why do electrons flow to positive from negative end of the cell in a circuit?

Answer 1

electrons are negative so they are repelled by the negative end and attracted to the positive end

Question 2

what are insulators?

Answer 2

materials that do not conduct electricity eg wood

Question 3

what are conductors?

Answer 3

materials that do conduct electricity eg metals

Question 4

why do conductors conduct?

Answer 4

delocalized sea of electrons is free to move, so free to flow through circuit and carry a charge

Question 5

why don’t insulators conduct?

Answer 5

electrons are fixed/ no delocalized electrons free to move

Question 6

what is an electrolyte?

Answer 6

• liquid that can conduct electricity
• ionic compound either molten or in solution

Question 7

what is electrolysis?

Answer 7

process of an electrolyte undergoing a chemical change

Question 8

why is electrolysis only carried out on (molten/ dissolved) ionic compounds ?

Answer 8

• no free ions in simple/giant covalent
• in molten/ dissolved ionic compounds there are ions which are free to move

Question 9

positive ion

Answer 9

cation

Question 10

negative ion

Answer 10

anion

Question 11

negative electrode

Answer 11

cathode

Question 12

what charge does the cathode have and why?

Answer 12

• negative
• surplus of electrons (so attracts cations)

Question 13

positive electrode

Answer 13

anode

Question 14

what charge does the anode have and why?

Answer 14

• positive
• shortage of electrons
• attracts anions

Question 15

what happens at the cathode?

Answer 15

• negative cathode attracts positive cations
• positive cations gain electrons from cathode
• REDUCTION (gain of electrons)
• metal of ionic compound formed

Question 16

what happens at the anode?

Answer 16

• positive anode attracts negative anions
• negative anions lose electrons to positive anode
• OXIDATION (loss of electrons)
• non-metal of ionic compound formed

Question 17

why does an electric current flow in electrolysis?

Answer 17

electrons are taken from the cathode and given to the anode so there is an overall flow of electrons/ electric current flows

Question 18

what is the industrial use of electrolysis?

Answer 18

used to extract metals that are more reactive than carbon so cannot be extracted through displacement by carbon

Question 19

example of metal industrially extracted through electrolysis

Answer 19

aluminium (bauxite, which is rich in aluminia/ Al203

Question 20

steps for the industrial extraction of aluminium

Answer 20

1. cryolite is added to the bauxite to lower its melting point and therefore reduce cost
2. aluminium oxide in bauxite must be melted
3. electricity is passed through the molten alumina to remove the oxygen through electrolysis

Question 21

why is aluminium expensive to make?

Answer 21

• large amount of heat energy needed to melt the alumina
• large amounts of electricity needed for electrolysis

Question 22

2 half equations for the electrolysis of aluminum and where do they each occur?

Answer 22

1. cathode : Al3+ + 3e- -> Al (reduction)
2. anode: 2O2- -> O2 + 4e-

Question 23

what is used to electrolyse aluminium?

Answer 23

hall cell (carbon anodes are periodically replaced as they react with the oxygen produced to make carbon dioxide which is released into the atmosphere)

Question 24

5 properties of aluminium

Answer 24

1. strong and malleable
2. low density
3. resistant to corrosion
4. good conductor of heat and electricity
5. highly reflective surface

Question 25

what ions are present in the electrolysis of solutions?

Answer 25

- non metal anion - metal cation - H+ and OH- from the water in the solution

Question 26

half equation for producing water and oxygen in electrolysis

Answer 26

- happens at anode - 4 OH- -> 4e- + 2H2O + O2 - OXIDATION

Question 27

how do you find out what is produced at the cathode in electrolysis of solutions?

Answer 27

- in a mixture of ions, cation that is lower in the reactivity series will gain electrons from the cathode - if the metal cation is lower than hydrogen in the reactivity series, the metal will be made - if hydrogen is lower than the metal ion, hydrogen will be produced

Question 28

what type of cell is used for electrolysis?

Answer 28

electrochemical cell (electrodes are connected to power supply)

Question 29

how can you purify copper through electrolysis?

Answer 29

1. using copper electrodes 2. copper in the impure anode forms copper ions which dissolve into the electrolyte 3. copper cations in electrolyte move to the pure copper to form a layer of pure copper 4. any impurities sink to bottom as sludge

Question 30

what happens at the cathode when purifying copper through electrolysis?

Answer 30

- Cu2+ + 2e- -> Cu - REDUCTION - mass of the cathode increases

Question 31

what happens at the anode when purifying copper through electrolysis?

Answer 31

- Cu -> Cu2+ + 2e- - OXIDATION - mass of anode decreases

Question 32

in electroplating, what is the cathode?

Answer 32

object to be plated

Question 33

in electroplating, what is the anode?

Answer 33

desired metal (metal that will plate the object)

Question 34

in electroplating, what is the electrolyte?

Answer 34

solution containing ions of the desired plating metal

Question 35

what are conductometric titrations?

Answer 35

titrations in which the electrical conductivity is measured as an acid is titrated against an alkali

Question 36

how does conductivity change from when an alkali is in excess to neutralization to when an acid is in excess? (conductometric titration)

Answer 36

- alkali in excess, so it is an aqueous ionic compound, so ions are free to move to conduct a charge - neutralization so precipitate (solid) formed so no ions free to move - acid in excess so ions are free to move to conduct a charge (v shaped graph)