electrolysis

Question 1

Why can ionic compounds have to be a liquid or dissolved for electrolysis (1)

Answer 1

so that the electrons are free to move and a current can be conducted

Question 2

Why do covalent compounds not conduct electricity (1)

Answer 2

they have no delocalized electrons that can carry charge

Question 3

what are positive ions called (1)

Answer 3

cations

Question 4

what are negaitve ions called (1)

Answer 4

anions

Question 5

what is the positive electrode called (1)

Answer 5

anode

Question 6

what is the negative electrode called (1)

Answer 6

cathode

Question 7

describe the experiment to investigate the electrolysis of lead bromide (6)

Answer 7

1. setup power supply
2. separate the rods and lower them into powder (lead bromide)
3. heat the powder in crucible
4. adjust current to 1.5 A
5. if white sheet placed behind apparatus the brown bromide can be seen
6. maintain current for 15 mins
7. if moist universal indicator paper is briefly held in the vapour it will turn red and may also be partially bleached
8. when cool remove the solidified metallic bead of lead and transfer it to a ceramic mat

Question 8

in the electrolysis of sodium carbonate solution, what are the products formed at each electrode (2)

Answer 8

cathode Hydorgen
anode oxygen gas (from hydroxide ions that are attracted to the anode, lose elctrons and form oxygen gas)

Question 9

why do you think the anode gets smaller over time in the electrolysis of potassium nitrate (2)

Answer 9

oxygen reacts with the carbon electrode forming CO2

Question 10

write the half-equations for the reactions occurring at each electrode in the electrolysis of potassium chloride solution label which is oxidation and which is reduction

Answer 10

2H+ + 2e- –> H2 reduction
2Cl- –> Cl2 + 2e- oxidation

Question 11

describe the experiment of the electrolysis of sodium chloride (5)

Answer 11

1. two electrodes (carbon) in two glass tubes surrounded by concentrated sodium chloride solution within a beaker with a rubber bung
2. two test tubes upside down must be in the beaker, the electrodes should go up these
3. the electrodes must be connected to a battery
4. add 4 drops of universal indicator and stir
5. once some gas has collected stop
6. use damp litmus paper to test gas at the anode

Question 12

describe the experiment of the electrolysis of dilute sulphuric acid (3)

Answer 12

1. setup Hoffman voltameter with power supply and sulphuric acid
2. glowing splint to test gas at anode
3. lit splint to test the gas at cathode

Question 13

describe the experiment of the electrolysis of coper(11) sulphate (3)

Answer 13

1. beaker with aqueous copper(11) sulphate solution and two carbon (graphite) electrodes connected to a power supply
2. electrodes in solution but not touching
3. DC power
4. 6 volts power

Question 14

what are the five parts of the Hoffman voltameter and what are their purposes (5)

Answer 14

1. bulb, shows if conducting
2. stopcock
3. central tube
4. anode, to attract the anions
5. cathode, to attract the cations

Question 15

write the ionic half equation for the electrolysis of sodium chloride (2)

Answer 15

2Na+ + 2e- –> 2Na
2Cl- –> Cl2 + 2e-

Question 16

write the ionic half equations for the electrolysis of sulphuric acid (2)

Answer 16

2H+ + 2e- –> H2
4OH- –> O2 + 2H2O + 4e-