Electrolosis Flashcards
Why can’t solids do electrolysis
The ions are locked in place by strong electrostatic forces of attraction and aren’t free to move. Can’t conduct electricity
How do you make a solid perform electrolysis
When an ionic compound is melted or dissolved in water , the forces of attractions are broken and ions are free to move . These liquids and solutions can now conduct electricity.(electrolytes)
How many electrodes are there
2-cathode (negative) and anode (positive)
What is electrodes made of
Made of a conductive but unreactive material (inert)
What happens during electrolysis
An electric current is passed through an electrolyte( molten or dissolved ionic compound ). The ions move towards the electrodes where they react and compound decomposes
What happens at cathode
Positive ions move towards cathode (-ve ) and gain electrons (reduction)
What happens at anode
The negative ions move towards the anode (+ve ) and lose electrons (oxidised )
Electrolysis of molten lead bromide-half equations
Pb(2+) +2e(1-) -> Pb reduction
2Br(1-) -2e(1-) -> Br2 oxidation
How to extract an ore
If a metal is less reactive than carbon or doesn’t reacts with carbon, it can be reduced
However if it is more reactive or reacts with carbon, it can be extracted with electrolysis
Reactivity series
Pottasium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold
What ionic compound and ore is aluminuim extracted from
Aluminium oxide comes from the bauxite ore
Properties of alumium
Low density ( used to make drink cans)
What ions do aluminuim oxide contain
Al(3+) and O(2-)
How do you lower aluminium melting point
Aluminium has a very high melting point of around 2000 Celcius therfore is mixed with cyolite to reduce amount of energy needed to save money
Why do we used graphic electrodes for electrolysis of aluminium
Because it an allotrope of carbon which is a very good conductor of electricity and very high melting point
What is attracted to the cathode in aluminium oxide
Al(3+) ions are attracted to the negative electrode and gains 3 electrons which turns into unchanged elemenet aluminium and sinks to the bottom
What is attracted to the anode in aluminium oxide
The negative O(2-) are attracted to the positive electrode where they lose 2 electrons. The oxygen atoms then combie to form O2 molecules
Half equations of electrolysis of alumnium oxide
Al(3+) + 3e(1-) -> Al - reduction
2O(2-) - 4e(1-) -> O2 - oxidation
Overall balanced equation for aluminium oxide
Aluminium oxide -> aluminuim + oxygen
2Al2O3 -> 4Al + 3O2
Why must the anode in electrolysis of aluminium oxide be replaced regularly
Because the oxygen molecules react with the graphite (carbon) to from carbon dioxide gas
Why is peoducing metals by electrolysis very expensive
Melting compounds such as aluminium oxide requires a great amount of energy
A lot of energy is required to produce the electric current
What is an aqueous solution
Dissolved in water
Water molecule ions
H20 -> Hydrogen ions H(1+) hydroxide ions
<- OH(1-)
Copper sulphate solution ions
Cu(2+) and SO4(2-)
H(1+) and OH(1-)
Which iron is reduced at the cathode in aqueous solutions
If the metal is more reactive than hydrogen,hydrogen will be reduced
If the metal is less reactive than hydrogen, the metal will be reduced at the cathode
What is reduced at the anode
Normally oxygen will be oxidised at the anode but if the iron is a halide , the halide will be reduced
Why do we use platinum electrodes for electrolysis of aqueous solution
Platinum doesn’t react will the chemicals we are making. It is inert
Half equation for aqueous solution Cu(2+)So4(2-)
Cu(2+) +2e(1-) -> Cu
4OH(1-) - 4e(1-) -> O2 +2H2O
Ions of NaCl Aqueous solution
Na(1+) Cl(1-)
H(1+) OH(1-)
Half equation for NaCl aqueous solution
2H(1+) +2e(1-) -> H2
2Cl(1-) -2e(1-) |-> Cl2
Electrolysis practical
Pour 50cm3 of copper chloride solution into a beaker and then place a plastic petri dish over the beaker which has 2 holes. Next insert a carbon graphite rod into each hole (electrodes) electrodes are inert. Make sure the electrodes don’t touch each other or there will be a short circut. Attach crocodile leads to rhe rods and connect the rods to the terminals of a low voltage power supply. Selct 4v and switch it on. The cathode should be coated with copper . The anode should have effervescence of chlorine gas. Can be tested by damp blue litmus paper, if it is chlorine , it will turn white
At the cathode , what will we see
A grey black deposit
