Chemistry - electrolysis

What is the cation in a compound

The positive ion, that loses electrons to have a full outer shell. Metal

What is the anion in a compound

The negative ion gains electrons to have a full outer shell. The non metal

Is the cation attracted to the cathode or the anode

cathode

Is the anion attracted to the cathode or the anode

anode

Is the cathode positive or negative? Why

Negative, as it has to attract the positive ion (cation)

Is the anode positive or negative? Why

Positive as it has to attract the negative ion (anion)

Define ions

The charged particles in ionic compounds

Define electrolysis

The process by which ionic substances are decomposed into simpler substances when an electric current is passed through them

Define electrolyte

A liquid which conducts electricity and is broken down. Electrolytes are usually molten ionic compounds or aqueous solutions of ionic compounds

Define electrodes

The rods which dip into the electrolyte. They are made of inert metals, which have high melting points and good electrical conductivity.

Define anode

The positive electrode which accepts electrons from the electrolyte

Define cathode

The negative electrode which donates electrons to the electrolyte

Do you use ac or dc power in electrolysis

dc

power supply (dc) Cathode Anode Cations Anions electrolyte

What does oil rig stand for?

Oxidation is loss, reduction is gain

Does oxidation or reduction happen at the anode? explain

Oxidation, losing electrons. The anion has gained electron to become an ion → so to get element back, you need to take electrons

Does oxidation or reduction happen at the cathode? explain

Reduction, gaining electrons. The cation has lost electron to become an ion → so to get element back, you need to add electrons

Lead bromide formula

PbBr2

What ions is lead bromide made up of

Pb 2+ and Br -

What bonds holds ions together in lead bromide

ionic

Can solid ionic compounds conduct electricity?

no

Can molten or aqueous compounds conduct

yes

Why don’t solid ionic compounds conduct electricity

The strong ionic bonds lock the ions in place, so they cannot conduct electricity

Why do molten or aqueous ionic compounds conduct electricity

The ions are able to move around and conduct electricity

Half equation for oxidation of bromide

2Br- (l) → Br2 (g) + 2e-

Half equation for the reduction of lead

Pb 2+ (l) + 2e- → Pb (s)

What do you see when a gas is produced in electrolysis

Bubbles at the electrode

What do you see when liquid is produced in electrolysis

The liquid is a different colour around the electrode

What do you see when solid is produced in electrolysis

A bead of metal at the bottom of the solution or coating the electrode

Graphite anode Graphite cathode Aluminium oxide dissolved in cryolite Molten alumium Steel case

Half equation at the cathode for the electrolysis of aluminium oxide

Al 3+ (l) + 3e- → Al (s)

Half equation at the anion for the electrolysis of aluminium oxide

2O2- (l) → O2 (g) + 4e-

Overall equation for the electrolysis of aluminium oxide

2Al2O3 (l) → 4Al (s) + 3O2 (g)

Environmental problems of the electrolysis of aluminium oxide

High cost due to huge amounts of electricity, because to produce 1 mole of aluminium (only 27g) you need 3 moles of electrons (because of high charge and low ram) Energy and material costs in constantly replacing the anodes (this is because they are made of carbon, and, due to the high temperature, the oxygen reacts with this to form co2, which gradually wears the anode away) Energy and material costs in replacing the cryolite, as some gets lost in electrolysis

How does recycling aluminium help?

Saves bauxite, which is finite resource Saves energy as much less energy is needed to melt aluminium than cryolite Reduces carbon dioxide released due to the oxygen reacting with carbon from the anode We need fewer bauxite mines, which are very destructive to natural habitats and cause deforestation Less waste material is produced so less landfill

Properties of aluminium

Low density, unreactive (an oxidised layer forms on the top and acts as a barrier), strong, conducts electricity, malleable, sonorous, ductile

Uses of aluminium

foil , cans, aircraft bodies, car bodies

What ore do get aluminium from

bauxite

Why can aluminium not be extracted using reduction with carbon

It is more reactive

Why and how is cryolite involved in the electrolysis of aluminium

Aluminium oxide must be molten or aqueous to conduct electricity, but its melting point is 2072. It is dissolved in molten cryolite which allows the process to occur at a lower temperature, saving energy

What is the cation rule for aqueous electrolysis

The substance lower down in the reactivity series is discharged. In water, this means that only copper, silver, and gold can be discharged, as they are the only metals less reactive than hydrogen

What is the anion rule for aqueous electrolysis

If a halide is present, it is discharged, if not, OH is discharged

Half equation for hydrogen being discharged

2H+ (aq) + 2e- → H2 (g)

What do you see if H is discharged

bubbles

Half equation for OH being discharged

4OH- (aq) → O2 (g) + 2H2O (l) + 4e-

What do you see if OH is discharged

Bubbles (of OXYGEN THE WATER STAYS IN THE WATER)