C3.4 Electrolysis

Question 1

Electrolysis definition

Answer 1

An Electric current is used to breakdown an ionic substance

Question 2

Electrolyte definition

Answer 2

The substance being broken down

Question 3

What substances does electrolysis work on?

Answer 3

Only works on substances made up of ions - ionic compounds, these are mostly the compounds of metals and non-metals

Question 4

When will Electrolysis work?

Answer 4

Will only work if the ions in the substance are free to move - will not work on solids but works on liquids, solutions and molten compounds

Question 5

Cathode

Answer 5

Negatively charged electrode, positively charged ions will go here to gain electrons

Question 6

Anode

Answer 6

Positively charged electrode, negatively charged ions will go here to lose electrons

Question 7

Cation

Answer 7

Positive ion - metal

Question 8

Anion

Answer 8

Negative ion - non-metal

Question 9

What does electrolysis do?

Answer 9

Turns ions back into atoms or molecules

Question 10

What electrode does oxidation occur?

Answer 10

Anode

Question 11

What electrode does Reduction occur?

Answer 11

Cathode

Question 12

What is a REDOX reaction?

Answer 12

a reduction-oxidation reaction, a chemical reaction where the oxidation number of an atom, molecule or ion changes by losing or gaining electrons

Question 13

Test for Oxygen

Answer 13

Relights a glowing splint

Question 14

Test for Hydrogen

Answer 14

‘Squeaky pop’ when lit

Question 15

PANIC

Answer 15

Positive Anode Negative Is Cathode

Question 16

Ionic half equations - sodium chloride

Answer 16

Sodium - Na+ + e- –> Na

Chloride - 2Cl- –> Cl2 + e-

Question 17

OILRIG

Answer 17

Oxidation Is Loss Reduction Is Gain

Question 18

LIPGIN

Answer 18

Loss Is Positive Gain Is Negative

Question 19

REDCAT

Answer 19

REDuction CAThode

Question 20

ANOX

Answer 20

ANode OXidation

Question 21

What is Brine?

Answer 21

An Aqueous solution

Question 22

What do water molecules break up into?

Answer 22

Hydrogen ions H+

Hydroxide ions OH-

Question 23

cations - positive ions - discharge series

Answer 23

harder –> easier to be discharged

Na+, Mg2+, Al3+, H+, Cu2+

Question 24

anions - negative ions - discharge series

Answer 24

harder –> easier to be discharged

SO42-, NO3, OH-,Cl-, Br-, I-

Question 25

if the ion is a halogen will it be discharged over hydroxide ions?

Answer 25

yes - halogen is discharged at the anode

Question 26

if the ion is not a halogen will it be discharged over hydroxide ions?

Answer 26

no, hydroxide ions from the water are discharged to make water and oxygen gas - other ions stay in solution

Question 27

if + ions (metals) are more reactive than hydrogen what is produced?

Answer 27

Hydrogen | - metals more reactive than hydrogen - K, Na, Ca, Mg, Zn, Fe

Question 28

if + ions (metals) are less reactive than hydrogen what is produced?

Answer 28

metal | - metals less reactive than hydrogen - Cu, Ag, Au

Question 29

if - ions are not halogens what is produced?

Answer 29

oxygen | - negative ions that aren't halogens - SO42-, NO3-, CO32-

Question 30

what electrodes are normally used in electrolysis?

Answer 30

carbon - inert (non-reactive) - don't take part in the reaction themselves

Question 31

what happens at a copper anode?

Answer 31

- as the anode is not inert, it loses electron and copper ions go into solution - anode gets smaller Cu (s) --> Cu2+ (aq) + 2e-

Question 32

what happens at a copper cathode?

Answer 32

``` copper ions (rather than hydrogen ions) are discharged because they are lower in the discharge series Cu2+ (aq) + 2e- --> Cu (s) ```

Question 33

describe the process of coper refining

Answer 33

- impure copper is used as anode - thin strip of copper used as cathode - solution of copper sulphate is used as electrolyte - a deposit of impurities from copper anode remain below anode (sludge)

Question 34

what happens in electroplating?

Answer 34

metal ions formed at anode are transferred to cathode where they are deposited as metal - plating the object (spoon) as / at the cathode

Question 35

uses for electroplating

Answer 35

- protect other more reactive metals from corrosion - e.g. steel coated in tin to protect it from air and water - improve appearance of objects - e.g. jewellery

Question 36

what are the most common plating metals used in electroplating?

Answer 36

- copper - chromium - nickel - silver - tin

Question 37

what ore do you get aluminium oxide from?

Answer 37

bauxite

Question 38

what is in bauxite?

Answer 38

the ore for aluminium oxide - has other metal oxides so have to separate before carrying out electrolysis of aluminium oxide