Chemical Changes Part 2

Question 1

what is electrolysis

Answer 1

when an ionic compound splits into its elements using electricity

Question 2

in which states can sodium chloride do electrolysis + why

Answer 2

molten and solution
ions are free to move

Question 3

process of electrolysis in molten sodium chloride

Answer 3

• sodium ion moves to the cathode because oposites attract
• chloride ion moves to the positive electrode because opposites attract
• sodium ion gains an electron to become a sodium atom. this is reduction.
  -chloride ion loses an electron to become a chlorine atom. this is oxidation.
  -sodium is made - silver solid
• chlorine is made - pale green gas and bubbles

Question 4

what is an electrolyte

Answer 4

an ionic compound you need to separate

Question 5

what are the electrodes made from

Answer 5

an inert substance (graphite or platinum)

Question 6

what are the uses of aluminium

Answer 6

foil
planes
cans

Question 7

what are the properties of aluminium

Answer 7

low density
conducts electricity
resistant to corrosion
malleable
conducts heat

Question 8

what happens in electrolysis of molten aluminium oxide

Answer 8

• separates in to Al 3+ and O 2-
• O2- will move to the positive electrode
• Al 3+ will move to the negative electrode
• aluminium is made at the negative electrode
• the oxide ion moves to the positive electrode but oxygen is not given off as it reacts with the carbon electrode to make carbon dioxide which is given off.

Question 9

what are the issues of using aluminium oxide

Answer 9

it needs a lot of energy and costs a lot of money (needs to be heated to 2500 degrees)

Question 10

how is the use of aluminium oxide made cheaper

Answer 10

they mix aluminium oxide with cryolite which lowers the melting point to 800 degrees and so it needs less energy

Question 11

how many ions are in the beaker in solutions

Answer 11

4 ions

Question 12

what are the steps of electrolysis of a solution

Answer 12

1- four ions in the beaker
2- ions move to the electrodes
3- ions are discharged
4- write half equations for each electrode
5- what is left in the container

Question 13

how do you work out which ion will be discharged at the electrodes

Answer 13

use the rules

Question 14

what are the rules for ionic solutions at the anode

Answer 14

if -ions are halogens the halogen is made
if - ions are not halogens oxygen is produced

Question 15

what are the rules for ionic solutions at the cathode

Answer 15

if +ions (metals) are more reactive than hydrogen then hydrogen is produced
if +ions (metals) are less reactive than hydrogen then the metal is produced

Question 16

what is inside a cell

Answer 16

chemicals that react together to produce electricity
the reactants create a supply of chemical potential energy

Question 17

how can a simple cell be made

Answer 17

dipping two different pieces of metal into a solution of ions which act as an electrolyte
the reaction between the two metals generate a voltage which can be measured using a voltmeter

Question 18

what determines the size of the voltage

Answer 18

concentration of the electrolyte
temperature of the electrolyte
type of electrolyte
type of electrode (which metals are used)

Question 19

what does the bigger the difference in reactivity of the metals mean

Answer 19

the bigger the voltage

Question 20

what produces no voltage

Answer 20

electrodes of the same material

Question 21

when will the voltage be a negative number

Answer 21

if an electrode is less reactive than the other metal

Question 22

example of rechargeable batteries

Answer 22

mobile phones
laptops

Question 23

properties of rechargeable batteries

Answer 23

can not be recharged
this is because the reaction used in the cells is reversible
the reaction will reverse when an electric current is applied

Question 24

examples of non rechargeable batteries

Answer 24

scales
remote control

Question 25

properties of non rechargeable batteries

Answer 25

cannot be recharged
this is because the reaction used in the cells is irreversible
this reaction will stop when one of the reactants have been used up

Question 26

how do fuel cells work

Answer 26

because a fuel (eg hydrogen ) is constantly supplied with a supply of oxygen
the hydrogen is oxidised to make water

Question 27

what are fuel cells an alternative to

Answer 27

using rechargeable batteries and cells

Question 28

what is the process of a fuel cell

Answer 28

hydrogen and oxygen are pumped into the fuel cell
the hydrogen atoms lose electrons and flow through the barrier
the electrons move round the circuit which generates a current
at the anode the electrons join with oxygen and hydrogen ions to produce water

Question 29

advantages of using hydrogen fuel cells over rechargeable cells

Answer 29

faster to refuel than recharging
lasts longer
hydrogen can be renewable
produces a constant voltage
no toxic chemicals released
no carbon dioxide given off

Question 30

disadvantages of using hydrogen fuel cells over rechargeable cells

Answer 30

hydrogen is made from fossil fuels
hydrogen is made from non renewable resources
hydrogen is difficult to store
hydrogen is flammable / explosive
costs more to refuel than recharge
costs more to manufacture
not many hydrogen filling stations