Electrolosis

Question 1

Why can’t solids do electrolysis

Answer 1

The ions are locked in place by strong electrostatic forces of attraction and aren’t free to move. Can’t conduct electricity

Question 2

How do you make a solid perform electrolysis

Answer 2

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)

Question 3

How many electrodes are there

Answer 3

2-cathode (negative) and anode (positive)

Question 4

What is electrodes made of

Answer 4

Made of a conductive but unreactive material (inert)

Question 5

What happens during electrolysis

Answer 5

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

Question 6

What happens at cathode

Answer 6

Positive ions move towards cathode (-ve ) and gain electrons (reduction)

Question 7

What happens at anode

Answer 7

The negative ions move towards the anode (+ve ) and lose electrons (oxidised )

Question 8

Electrolysis of molten lead bromide-half equations

Answer 8

Pb(2+) +2e(1-) -> Pb reduction

2Br(1-) -2e(1-) -> Br2 oxidation

Question 9

How to extract an ore

Answer 9

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

Question 10

Reactivity series

Answer 10

Pottasium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold

Question 11

What ionic compound and ore is aluminuim extracted from

Answer 11

Aluminium oxide comes from the bauxite ore

Question 12

Properties of alumium

Answer 12

Low density ( used to make drink cans)

Question 13

What ions do aluminuim oxide contain

Answer 13

Al(3+) and O(2-)

Question 14

How do you lower aluminium melting point

Answer 14

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

Question 15

Why do we used graphic electrodes for electrolysis of aluminium

Answer 15

Because it an allotrope of carbon which is a very good conductor of electricity and very high melting point

Question 16

What is attracted to the cathode in aluminium oxide

Answer 16

Al(3+) ions are attracted to the negative electrode and gains 3 electrons which turns into unchanged elemenet aluminium and sinks to the bottom

Question 17

What is attracted to the anode in aluminium oxide

Answer 17

The negative O(2-) are attracted to the positive electrode where they lose 2 electrons. The oxygen atoms then combie to form O2 molecules

Question 18

Half equations of electrolysis of alumnium oxide

Answer 18

Al(3+) + 3e(1-) -> Al - reduction

2O(2-) - 4e(1-) -> O2 - oxidation

Question 19

Overall balanced equation for aluminium oxide

Answer 19

Aluminium oxide -> aluminuim + oxygen
2Al2O3 -> 4Al + 3O2

Question 20

Why must the anode in electrolysis of aluminium oxide be replaced regularly

Answer 20

Because the oxygen molecules react with the graphite (carbon) to from carbon dioxide gas

Question 21

Why is peoducing metals by electrolysis very expensive

Answer 21

Melting compounds such as aluminium oxide requires a great amount of energy

A lot of energy is required to produce the electric current

Question 22

What is an aqueous solution

Answer 22

Dissolved in water

Question 23

Water molecule ions

Answer 23

H20 -> Hydrogen ions H(1+) hydroxide ions
<- OH(1-)

Question 24

Copper sulphate solution ions

Answer 24

Cu(2+) and SO4(2-)

H(1+) and OH(1-)

Question 25

Which iron is reduced at the cathode in aqueous solutions

Answer 25

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

Question 26

What is reduced at the anode

Answer 26

Normally oxygen will be oxidised at the anode but if the iron is a halide , the halide will be reduced

Question 27

Why do we use platinum electrodes for electrolysis of aqueous solution

Answer 27

Platinum doesn’t react will the chemicals we are making. It is inert

Question 28

Half equation for aqueous solution Cu(2+)So4(2-)

Answer 28

Cu(2+) +2e(1-) -> Cu

4OH(1-) - 4e(1-) -> O2 +2H2O

Question 29

Ions of NaCl Aqueous solution

Answer 29

Na(1+) Cl(1-)

H(1+) OH(1-)

Question 30

Half equation for NaCl aqueous solution

Answer 30

2H(1+) +2e(1-) -> H2

2Cl(1-) -2e(1-) |-> Cl2

Question 31

Electrolysis practical

Answer 31

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

Question 32

At the cathode , what will we see

Answer 32

A grey black deposit