AQA GCSE Chemistry Year 10: Electrolysis

What is electrolysis?

The process through which an ionic compound is split using electricity. For the ions to move the compound must be molten or dissolved.

What are the liquids and solutions which electrolysis happens to called?

electrolytes

What happens when you pass an electric current through the electrolytes?

the ions move to the electrodes with the opposite charge to theirs

What is the negative electrode in electrolysis called?

cathode

What is the positive electrode in electrolysis called?

anode

What are electrodes generally made of and why?

Graphite

. inert

. cheap

. good conductor

. insoluble

What type of current must be used for electrolysis?

Direct current (DC)

In the electrolysis of a molten ionic compound what happens to the metal ion?

. attracted to cathode

. Reduced (gains electrons to complete outer shell and form elemental metal)

In the electrolysis of a molten ionic compound what happens to the non-metal ion?

. attracted to anode

. Oxidised (loses electrons to complete outer shell and form elemental non-metal)

When would we use electrolysis to extract a metal?

. if the metal is too reactive to be extracted by reduction with carbon

. if the metal reacts with carbon

What is aluminium oxide sometimes called?

bauxite

What is the formula for aluminium oxide?

Al2O3

How is aluminium extracted from bauxite?

. electrolysis of molten mixture of bauxite and cryolite

. mixture has a lower melting point than bauxite so it saves energy

. Aluminium ions are reduced at cathode

. Oxide ions are oxidised at anode

. Anode is made of graphite (carbon) which reacts with the oxygen to form CO2 so must be continually replaced

Why might carbon monoxide be produced at the anode when oxygen is formed there?

. Don't bring up unless asked

. Graphite (carbon) anode can react with limited oxygen to form carbon monoxide

Why is aluminium, a reactive metal, resistant to corrosion?

has a protective oxide layer

What 4 ions are present in the electrolysis of an aqueous ionic compound?

. positive metal ion

. negative non-metal ion

. water dissociates to form: H+ and OH-

How do you know which ion will be reduced at the cathode in the electrolysis of an aqueous solution?

. Positive ions attracted to cathode

. Whichever is lowest in the reactivity series gains the electron most easily, so is reduced

. This will be hydrogen unless copper (Cu2+) or silver (Ag+) are present

How do you know which ion will be oxidised at the anode in the electrolysis of an aqueous solution?

. Negative ions attracted to anode

. If a group 7 ion is present, this will form a diatomic molecule of that halogen

. If not, the hydroxide ion will be oxidised in the equation:

4OH- (aq) -> 2H2O (l) + O2 (g) + 4e-

What are the products of the electrolysis of aqueous solutions?

. product at cathode

. product at anode

. ions left over react (if they react with each other) and form another product

How can you tell which is the anode and which is the cathode if you're unsure?

AN OX, RED CAT

(anode oxidation, reduction cathode)

What is oxidation and reduction?

Oxidation is loss of electrons

Reduction is gain of electrons

What direction do electrons flow?

from negative to positive

Pros and cons of using molten ionic compounds

. Giant ionic lattice requires a lot of energy to melt

. Only 2 ions present

What do you call aqueous sodium chloride?

brine

What can hydrogen be used as?

fuel

What can chlorine be used for?

to kill bacteria

What can sodium hydroxide be used for?

to make bleach