Electrolysis revision!

Electrolysis revision!

Starter:

Why do we take repeats in experiments?

Starter answer

We calculate repeats in experiment to

- Identify anomalies

- Calculate a mean

- increase the reliability of results

Multiple Choice

Ionic bonding is bonding between

• Metals and metals

• Non-metals and non-metals

• Metals and non-metals

Electrolysis

• Electrolysis is the splitting up of an ionic compound using electricity

• The ionic compound has to be melted or aqueous (dissolved in water)

• This is so the ions are free to move and conduct electricity

• The melted/aqueous solution of the ionic compound is called the electrolyte

Multiple Choice

What is electrolysis

• The splitting of a metallic compound using electricity

• The splitting of an ionic compound using electricity

• The splitting of a covalent compound using electricity

Multiple Select

What state must the ionic compound be in for electrolysis to work? (select 2)

• Solid

• Liquid

• Gas

• Aqueous

Multiple Choice

What is the name of the liquid/solution of the ionic compound

• Electrode

• Electrolysis

• Electron

• Electrolyte

Multiple Select

Why does the ionic compound need to be melted/in aqueous solution (select 2)

• So the ions are charged

• So the ions can move

• So the ions can conduct electricity

• So the ions can dissolve

Electrolysis

• Two electrodes are connected to a cell and dipped into the electrolyte solution

• The electrode connected to the positive cell terminal is the anode

• The electrode connected to the negative cell terminal is the cathode

Multiple Choice

Opposite charges

• attract each other

• repel each other

Multiple Choice

The electrode connected to the negative terminal of the cell is called the

• Anode

• Cathode

• Cation

• Anion

Multiple Choice

The electrode connected to the positive terminal of the cell is called the

• Anode

• Cathode

• Cation

• Anion

Electrolysis

• The negative ions from the ionic compound are called anions and they are attracted to the positive anode

• The positive ions from the ionic compound are called cations and they are attracted to the negative cathode

Multiple Choice

The positive ion in the electrolyte is the

• Anode

• Cathode

• Cation

• Anion

Multiple Choice

The negative ion in the electrolyte is the

• Anode

• Cathode

• Cation

• Anion

Multiple Choice

The cation is attracted to the

• Anode

• Cathode

• Cation

• Anion

Multiple Choice

The anion is attracted to the

• Anode

• Cathode

• Cation

• Anion

Electrolysis

• The electrodes must be made of unreactive metals so they don't react with the electrolyte solution

What happens at each electrode?

• Remember OILRIG - oxidation is loss of electrons, reduction is gain

• Anions go to the anode and are oxidised

• Cations go to the cathode and are reduced

At the anode

• Anions are oxidised (lose electrons) and elements are discharged

• When the ionic compound is in molten state, non-metals are produced at the anode

At the cathode

• Cations are reduced (gain electrons) and elements are discharged

• When the ionic compound is in molten state, metals are produced at the cathode

Multiple Choice

Metals usually form at the

• Cathode

• Anode

Multiple Choice

Non-metals usually form at the

• Cathode

• Anode

Multiple Choice

Why do electrodes need to be made of inert (unreactive) metals

• So they break up into ions

• So they cannot conduct electricity

• So they don't react with the electrolyte solution

• So they do react with the electrolyte solution

Multiple Choice

At the anode, anions are

• Oxidised (lose electrons)

• Reduced (gain electrons)

Multiple Choice

At the cathode, cations are

• Oxidised (lose electrons)

• Reduced (gain electrons)

Electrolysis of aqueous compounds

• During electrolysis, ionic compounds are split into their ions

• If the ionic compound has been dissolved in water, then water will also split. 

• E.g. Aqueous NaCl is split into Na+, Cl-, H+ and OH-

Multiple Select

During electrolysis of aqueous NaCl, which ions will move to the cathode?

• Na+

• Cl-

• H+

• OH-

Electrolysis of aqueous compounds

• At the cathode, the less reactive cation will be reduced

• The more reactive cation will stay in the electrolyte solution

• E.g. if Na+ and H+ are the cations, hydrogen is less reactive than sodium and the hydrogen ions are reduced

Electrolysis of aqueous compounds

• At the anode, the OH- anions will be oxidised to oxygen gas and water

• BUT if group 7 (halide) ions are present, they will be oxidised instead.

• Eg if OH- and Cl- are the anions, the Cl- anions are oxidised to Chlorine gas

Electrolysis of aqueous compounds

• In the electrolyte solution, the ions that haven't been oxidised or reduced will react with each other

Multiple Choice

During the electrolysis of an aqueous compound, what is reduced at the cathode?

• The more reactive cation

• The less reactive cation

Electrolysis of aluminium oxide

Aluminium is extracted from its ore (bauxite) which contains aluminium oxide.

Molten aluminium oxide undergoes electrolysis and pure aluminium is obtained.

Aluminium is too reactive to be extracted via reduction with carbon, it sits above carbon on the reactivity series.

Electrolysis is expensive.

Multiple Select

Why is electrolysis of aluminium oxide expensive? (pick 2)

• Low temperatures are required

• High temperatures are required

• Lots of energy is needed for the process

• Little energy is needed for the process

Electrolysis of aluminium oxide

Cryolite is mixed with aluminium oxide to lower the melting point of the compound.

The molten aluminium oxide is made up of positive aluminium ions and negative oxygen ions

Multiple Choice

Which ions move to the cathode?

• The positive aluminium ions

• The negative oxygen ions

Multiple Choice

Which ions move to the anode?

• The positive aluminium ions

• The negative oxygen ions

Electrolysis of aluminium oxide

At the cathode, the positive aluminium cations are reduced, pure aluminium metal is formed.

Electrolysis of aluminium oxide

At the anode, the negative oxygen anions are oxidised, oxygen is formed.

Electrolysis of aluminium oxide

The anode is made of carbon. Oxygen gas is made at the anode. This reacts with the carbon anode to form carbon dioxide gas. This means the carbon gets used up and the anodes must be replaced regularly.