Topic 3 - Electrolytic Processes

Question 1

How does electrolysis work?

Answer 1

Electricity supplied to electrolyte (an ionic substance thats either molten or dissolved in water) and free ions in an electrolyte conduct electricity which decomposes a compound.

Question 2

Are electrons given or taken away from ions at positive anode

Answer 2

taken away

Question 3

what are positive ions called

Answer 3

cations

Question 4

what are negative ions called

Answer 4

anions

Question 5

What is oxidation and reduction in terms of electrons

Answer 5

Oxidation Is Loss Reduction Is Gain

Question 6

What happens with the electrolysis of molten sodium chloride

Answer 6

Sodium is produced at the cathode and chlorine at the anode.

Question 7

What are the half equations of electrolysis of molten NaCl

Answer 7

cathode : Na⁺ e^- -> Na

Anode: 2Cl- -> Cl₂ + e^-

Question 8

What is Sodium used for

Answer 8

used in street lamps

coolant in some nuclear reactors

Question 9

What is produced when you electrolyse molten lead bromide

Answer 9

Lead (l) is produced at the cathode

Bromine (g) is produced at the anode

Question 10

what are the half equations of electrolysis of molten lead bromide

Answer 10

Cathode: Pb²⁺ + 2e^- -> Pb

Anode: 2Br^- -> Br₂ + 2e^-

Question 11

Why do electrolytes behave differently in solution to molten ones

Answer 11

In solution there is the presence of H⁺ and OH^- ions from the water

Question 12

What happens at the anode when the electroylte is in solution

Answer 12

the ‘simplist’ ion is discharged

e.g Cl^- is discharged rather than OH^- and OH^- rather than SO₄^2-

Question 13

What happens at the cathode when the electrolyte is in solution

Answer 13

a metal will be discharged if it is less reactive than hydrogen, if the metal is more reactivge than hydrogen, the hydrogen will be discharged.

Question 14

Why does copper need to be purified

Answer 14

once extracted from ore not pure enought for use in electrical conductors

Question 15

How do you purify copper

Answer 15

anode is impure copper, cathode starts as thin strip of pure copper. Electolyte is copper (II) sulfate solution.

Electrical suplly works by pulling atoms off the copper atoms at the anode causeing them to go into solution as Cu²⁺ ions then offering electrons at the cathode to near by Cu²⁺ ions to turn them back to copper atoms.

Impurites dropped at the anode as a sludge whilst pure copper atoms bond to the cathode.

Question 16

What are the half equations for purifying copper

Answer 16

cathode: Cu²⁺_(aq) + 2e^- -> Cu _(s)

Anode: Cu _(s) -> Cu²⁺ _(aq) + 2e^-

Question 17

How do you demostrate the mass change in the electrolysis of impure copper

Answer 17

weigh anode and cathode before electrolysis

place electrodes in copper sulfate solution and connect to power pack

after 5 min switch of power pack, remove electrodes and dry them

weigh anode and cathode again.

mass of anode will decrease, mass of cathode will increase

Question 18

What is electroplating

Answer 18

coating the surface of a metal with another metal using electricity

Question 19

How do you do electroplating

Answer 19

Put the object youre going to electroplate at the cathode and a bar of the metal used for plating at the anode. electolyte is solution containing metal used for plating.

Question 20

What are the uses of electorplating

Answer 20

decoration - jewellery and decorative itmes are often electroplated with metals like gold or silver which improves appearance of metals making them look shiny and attractive.

Prevention of corrosion - household objects like cutlery and cooking utensils are electroplated with metals to stop them corroding. metals used for protection are unreactive and dont corrode easily (e.g nickel or chromiom)