chemical change (electrolysis) (paper 1)

Question 1

electrolysis

Answer 1

when an ionic compound splits into its elements using electricity

Question 2

do solid ionic compounds conduct electricity

Answer 2

no because the ions are fixed

Question 3

do molten ionic compounds and ionic compounds in a solution conduct electricty

Answer 3

yes because the ions are free to move

Question 4

what is the ionic compound you need to separate called

Answer 4

the electrolyte

Question 5

what are the electrodes made from

Answer 5

an inert (un reactive) substance eg graphite or platinum

Question 6

how many ions are in the beaker during electrolysis of a molten compound

Answer 6

2

Question 7

explain the steps of electrolysis of a molten compound

Answer 7

1. the positive ion moves to the negative electrode because opposites attract
2. the negative ion moves to the positive electrode because opposites attract
3. _____ ion gains an electron to become a _____ atom. this is reduction
4. then say what substance is made at the electrode
5. ____ ion loses an electron to become a ____ atom. this is oxidation
6. then say what is made at the positive electrode

Question 8

electrolysis of motlen aluminium oxide

Answer 8

molten aluminium oxide seperates into aluminium and oxygen

oxygen will move to the positive electrode because opposites attract

aluminium will move to the negative electrode because opposites attract

oxygen is made at the positive electrode

aluminium is made at the negative electrode

Question 9

the problems with aluminium oxide

Answer 9

the oxygen reacts with the carbon electrode to make carbon dioxide which wears the positive electrode away and then it needs replacing

for electrolysis aluminium oxide has to be heated to 2500 degrees , this needs a lot of energy and costs a lot of money

Question 10

what is cryolite

Answer 10

a substance that gets mixed with aluminium oxide which lowers the melting point to 800 degrees so it needs less energy and costs them less money

Question 11

in electrolysis of solution how many ions are in the beaker

Answer 11

4

Question 12

what ions do water molecules seperate
into

Answer 12

H+

OH-

Question 13

rules for ionic solutions at the anode

Answer 13

if the ions are halogens , the HALOGEN is made

if the ions are NOT halogens , oxygen is produced

Question 14

rules for ionic solutions at the cathode

Answer 14

if the ions are MORE REACTIVE than hydrogen , then HYDROGEN is produced

if the ions are less reactive than hydrogen , the METAL is produced

Question 15

in a chemical cell what is the size of the voltage determined by

Answer 15

concentration of electrolyte

temperature of electrolyte

type of electrolyte

type of electrode

Question 16

what does the bigger difference in reactivity between the two metals do in a chemical cell

Answer 16

the more reactive = more voltage

Question 17

what is the voltage like of electrodes of the same material in a chemical cell

Answer 17

there is no voltage produced

Question 18

why can rechargeable batteries be recharged

Answer 18

the reaction used in the cell is reversible

the reaction will reverse when an electric current is applied

Question 19

why can non rechargeable batteries not be recharged

Answer 19

the reaction used in the cell is irreversible

the reaction will stop when one of the reactants has been used up

Question 20

what are fuel cells

Answer 20

a fuel (eg hydrogen) is constantly supplied with a supply of oxygen

the hydrogen is oxidised to make water

equation : 2H2 +O2 ——> 2H2O

Question 21

how do fuel cells work

Answer 21

hydrogen and oxygen are pumped into the fuel cell

the hydrogen atom lose electrons to become hydrogen ions and flow through the barrier

the electrons move around the circuit which generates a current

at the anode the electrons join with oxygen and hydrogen ions to produce water

Question 22

advantages of using hydrogen fuel cells over rechargeable cells

Answer 22

faster to refuel than recharging

lasts longer

hydrogen can be renewable

produces a constant voltage

no carbon dioxide given off

Question 23

disadvantages of using hydrogen fuel cells over rechargeable cells

Answer 23

hydrogen is made form fossil fuels

hydrogen is made from non renewable resources

hydrogen is difficult to store

Question 24

how many ions are there in an aqueous solution during electrolysis

Answer 24

4

Question 25

what ions are there always in an aqueous solution during electrolysis

Answer 25

H+ and OH-

Question 26

what is the test for chlorine gas

Answer 26

bleaches damp litmus paper, turning it white