C6- Electrolysis

Question 1

electrolyte

Answer 1

a liquid, containing free-moving ions, which is broken down by electricity in the process of electrolysis

Question 2

anode

Answer 2

positive electrode in electrolysis

Question 3

cathode

Answer 3

negative electrode in electrolysis

Question 4

inert

Answer 4

unreactive

Question 5

half equations

Answer 5

an equation that describes reduction (gain of electrons) or oxidation (loss of electrons)

Question 6

brine

Answer 6

concentration sodium chloride solution

Question 7

electrolysis

Answer 7

use of an electric current to break down an ionic compound

Question 8

what happens during electrolysis

Answer 8

• positively charged ions move to the cathode
• negative ions move to the anode
• as opposite charges attract

Question 9

ionic compound circumstance for electrolysis

Answer 9

• molten or dissolved in water
• end substance more unknown in water
• ions are then free to move and carry their charge to the electrodes

Question 10

covalent compound circumstance for electrolysis

Answer 10

-react in water to form ions

Question 11

what happens to the state symbols in the electrolysis of copper bromide

Answer 11

aq —> s + aq

Question 12

what does ionic substances have high melting points mean

Answer 12

-so it takes a lot of energy to melt them and free the ions to move to the electrodes in electrolysis

Question 13

why is it more difficult to know what will be formed with ionic compounds in solution

Answer 13

• water also forms ions

- products at each electrode are not always exactly what you expect

Question 14

which metals are deposited from their aqueous solutions

Answer 14

metals very low in reactivity, below hydrogen

Question 15

what do you observe at the electrodes when you electrolyse copper bromide

Answer 15

• Cu2+ moves to cathode, copper forming, colour change

- Br- moves to anode, fizzing, giving of gas

Question 16

why a mixture of aluminium oxide plus cryolite is used

Answer 16

lowers melting point of aluminium oxide, reducing the energy needed to extract aluminium

Question 17

why the positive electrode has to be replaced at regular intervals in aluminium extraction

Answer 17

they gradually burn away as the oxygen reacts with the hot carbon anodes, forming carbon dioxide gas

Question 18

why is aluminium expensive

Answer 18

large amounts of energy is used in the extraction process

Question 19

what can Al2O3 also called

Answer 19

bauxite + cryolite

Question 20

half equations for electrolysis of aluminium and at which electrodes they form

Answer 20

• Al3+ + 3e- —> Al (cathode)

- 2O2- —> O2 + 4e- (anode)

Question 21

+ Ions

Answer 21

• ions of elements lower in the reactivity series are easier to discharge
• solutions containing a high reactivity metal, h+ ions discharge instead

Question 22

• Ions

Answer 22

-if compound is in group 7 it is discharged

if not OH- is discharged

Question 23

H+, what is formed in electrolysis and the half equation

Answer 23

H2,

2H+ + 2e- —> H2

Question 24

OH-, what is formed in electrolysis and the half equation

Answer 24

O2,

4OH- - 4e- —> O2 + 2H2O

Question 25

oxidation

Answer 25

loss of electrons + gain of oxygen

Question 26

reduction

Answer 26

gain of electrons + loss of oxygen

Question 27

three products of electrolysis of sodium chloride solution

Answer 27

chlorine and hydrogen gas given off at electrodes, sodium hydroxide solution left in solution

Question 28

what are produced at different electrodes one electrolysis of sodium chloride solution

Answer 28

• hydrogen at cathode, H+ over Na+

- chlorine at anode, Cl- over OH-

Question 29

what usually appears at cathode in electrolysis of aqueous solutions

Answer 29

less reactive element, hydrogen or the metal

Question 30

what usually appears at anode in electrolysis of aqueous solutions

Answer 30

• oxygen gas given off, from discharged hydroxide ions produced from water
• a halogen produced in electrolyte is a solution of a halide