Chemical Changes Part 2 Flashcards
what is electrolysis
when an ionic compound splits into its elements using electricity
in which states can sodium chloride do electrolysis + why
molten and solution
ions are free to move
process of electrolysis in molten sodium chloride
- 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
what is an electrolyte
an ionic compound you need to separate
what are the electrodes made from
an inert substance (graphite or platinum)
what are the uses of aluminium
foil
planes
cans
what are the properties of aluminium
low density
conducts electricity
resistant to corrosion
malleable
conducts heat
what happens in electrolysis of molten aluminium oxide
- 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.
what are the issues of using aluminium oxide
it needs a lot of energy and costs a lot of money (needs to be heated to 2500 degrees)
how is the use of aluminium oxide made cheaper
they mix aluminium oxide with cryolite which lowers the melting point to 800 degrees and so it needs less energy
how many ions are in the beaker in solutions
4 ions
what are the steps of electrolysis of a solution
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
how do you work out which ion will be discharged at the electrodes
use the rules
what are the rules for ionic solutions at the anode
if -ions are halogens the halogen is made
if - ions are not halogens oxygen is produced
what are the rules for ionic solutions at the cathode
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
what is inside a cell
chemicals that react together to produce electricity
the reactants create a supply of chemical potential energy
how can a simple cell be made
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
what determines the size of the voltage
concentration of the electrolyte
temperature of the electrolyte
type of electrolyte
type of electrode (which metals are used)
what does the bigger the difference in reactivity of the metals mean
the bigger the voltage
what produces no voltage
electrodes of the same material
when will the voltage be a negative number
if an electrode is less reactive than the other metal
example of rechargeable batteries
mobile phones
laptops
properties of rechargeable batteries
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
examples of non rechargeable batteries
scales
remote control
properties of non rechargeable batteries
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
how do fuel cells work
because a fuel (eg hydrogen ) is constantly supplied with a supply of oxygen
the hydrogen is oxidised to make water
what are fuel cells an alternative to
using rechargeable batteries and cells
what is the process of a fuel cell
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
advantages of using hydrogen fuel cells over rechargeable cells
faster to refuel than recharging
lasts longer
hydrogen can be renewable
produces a constant voltage
no toxic chemicals released
no carbon dioxide given off
disadvantages of using hydrogen fuel cells over rechargeable cells
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
