Electrolysis

Question 1

define electricity

Answer 1

flow of electrons/charge

Question 2

what is a conductor?

Answer 2

a solid material which allows charge to flow through it

Question 3

what is an insulator?

Answer 3

a material which does not allow charge to flow through it

Question 4

how do metals like iron and non metals like graphite allow charge to flow through them?

Answer 4

they have free delocalised electrons not used in bonding

Question 5

why do non metals such as diamond and sulfur not allow charge to flow through them?

Answer 5

all electrons are used in bonding, so cannot flow

Question 6

what is an electrolyte?

Answer 6

an ionic compound in the molten state or dissolved in water

Question 7

what is electrolysis?

Answer 7

the process of a liquid (electrolyte) conducting electricity, bringing about a chemical change in the electrolyte

Question 8

what types of compound can electrolysis be carried out on?

Answer 8

ionic

Question 9

can ionic compounds conduct electricity while solid and why?

Answer 9

no, because there are no free ions or electrons

Question 10

can ionic compounds conduct electricity while molten/dissolved and why?

Answer 10

yes, because charged ions are free to move around

Question 11

the electrode connected to the negative terminal will be _____ charged

Answer 11

negatively

Question 12

the electrode connected to the positive terminal will be _____ charged

Answer 12

positively

Question 13

the negative electrode is called the…

Answer 13

cathode

Question 14

the positive electrode is called the…

Answer 14

anode

Question 15

positively charged ions are called?

Answer 15

cations

Question 16

positively charged cations are attracted to what?

Answer 16

the cathode

Question 17

negatively charged ions are called?

Answer 17

anions

Question 18

negatively charged anions are attracted to what?

Answer 18

the anode?

Question 19

what type of reaction happens at the cathode?

Answer 19

reduction

Question 20

what type of reaction happens at the anode?

Answer 20

oxidation

Question 21

why is the cathode negative?

Answer 21

it has a surplus of electrons

Question 22

why is the anode positive?

Answer 22

it has a deficit of electrons

Question 23

what happens to the positive ion of a molten ionic compound during electrolysis?

Answer 23

• molten makes it free to move
• attracted to cathode as opposite charges attract
• take electrons from the cathode to form an atom (is reduced)

Question 24

what happens to the negative ion of a molten ionic compound during electrolysis?

Answer 24

• molten makes it free to move
• attracted to anode as opposite charges attract
• donate electrons to the cathode to form an atom (is oxidised)

Question 25

how is aluminium extracted?

Answer 25

- mined as Al₂O₃ in bauxite - mixed with cryolite to dissolve the Al₂O₃ instead of melting it, as it has a high mp, which would require lots of energy - current is passed through to separate Al from O² (describe electrolysis)

Question 26

what is different about electrolysis in a solution from electrolysis in molten state?

Answer 26

- because H+ and OH- ions are also present from the water, they compete for which ions will be oxidised/reduced

Question 27

what determines which ion is produced at the cathode during electrolysis of a solution?

Answer 27

- both positive ion from ionic compound and H+ ion from water present - If H+ is below the metal in the reactivity series, H+ is reduced - If H+ is above the metal in the reactivity series (Ag, Cu), then the metal ion is reduced

Question 28

what determines which ion is produced at the anode during electrolysis of a solution?

Answer 28

- both negative ion from ionic compound and OH- ion from water present - If the ion from the ionic compound is a halide (Cl-, Br- etc) then they are oxidised and the OH- stays in the solution - If the ion from the ionic compound isn't a halide (SO₄²-, NO₃- etc) then they stay in solution and the OH- is oxidised

Question 29

Balanced half equation for reduction of H+ at the cathode?

Answer 29

2H+ +2e- -> H²

Question 30

Balanced half equation for oxidation of OH- at the anode?

Answer 30

4OH- -> 2H₂O + O₂ + 4e-

Question 31

in the electrolysis of sulfuric acid, will more H₂ or O₂ be produced and why?

Answer 31

- More H₂, as H+ only requires one electron transfer to form into an atom, or 2 to form a diatomic molecule - Whereas O²- requires 2 electron transfers to form into an atom, or 4 to produce a diatomic molecule - Meaning it'll be produced at half the rate of H₂