Electrolysis

What is the literal meaning of electrolysis?

'breaking something apart by electricity'

What is electrolysis?

The breaking apart of ionic substances by pulling the positive and negative ions in different directions towards negative and positive electrodes - reforming atoms from ions

What kind of reaction is electrolysis?

A redox reaction - a reaction where oxidation and reduction happen at the same time

What is oxidation?

the loss of electrons

What is reduction?

the gain of electrons

What is the name for the positive electrode?

the anode

What is the name for the negative electrode?

the cathode

What are electrodes made up of?

Very unreactive metals - inert materials that conduct electricity such as graphite

What ions collect at the anode?

Anions (negative ions)

What ions collect at the cathode?

Cations (positive ions)

What occurs at the anode?

Oxidation - the negative ions (anions) lose electrons to form neutral atoms

What occurs at the cathode?

Reduction - the positive ions (cations) gain electrons to form neutral atoms

What is the electrolyte?

The solution that contains the positive and negative ions meaning it can therefore conduct electricity

Molten ionic salts are liquid ionic compounds so can therefore conduct electricity

Don't panic mnemonic

positive

anode

negative

is

cathode

What happens at the cathode?

The cation gains as many electrons as it needs from the negatively charged cathode to become a neutral atom

What happens at the anode?

The anion loses as many electrons as it needs to become a neutral atom

Diatomic molecules

Hydrogen, nitrogen, fluorine, oxygen, iodine, chlorine and bromine

What is electrolysis in solutions?

When an ionic compound is dissolved in water, H+ and OH- ions are also present and 'compete' to gain/lose electrons at the cathode/anode

What happens at the anode in an aqueous solution?

If a halogen is present, then it is released

If no halogen is present, then oxygen is released

What happens at the cathode in an aqueous solution?

If the metal is less reactive than hydrogen, the metal is deposited

If the metal is more reactive than hydrogen, hydrogen is released

What metals are less reactive than hydrogen?

Copper, silver and gold

What is brine?

Sodium chloride in water

Oxygen half equation

4OH- -> O2 + 4e- + 2H2O

Hydrogen half equation

2H+ + 2e- --> H2

What is produced at the cathode in brine?

Hydrogen

What is produced at the anode in brine?

Chlorine

2Cl- --> Cl2 + 2e-

Uses of hydrogen gas

margarine, rocked fuel and reducing metal ores

Uses of chlorine gas

bleach, water sterilisation and plastic making

uses of sodium hydroxide

making soap, explosives and dyes

What ions are present in aqueous solutions?

H+ and OH-

What is aluminium used for?

In aircraft and industry due to it being lightweight and resistant to corrosion

What material is used for the electrodes (Al)?

Graphite

What is the aluminium ore dissolved in?

Cryolite which lowers the melting points so requires less energy meaning its cheaper

Why must molten aluminium be used?

Aluminium is more reactive than hydrogen so in an aqueous solution, hydrogen would be produced

What gas is produced in electrolysis of aluminium?

Oxygen

Why must the anodes be regularly replaced?

Due to high temperatures, oxygen reacts with carbon in the anode to produce carbon dioxide which causes the anodes to corrode away

What will happen to litmus paper if chlorine is found to be present?

The blue litmus paper will be bleached white

What will happen if oxygen is present?

Bubbles will form at the electrode

What will happen if copper is present?

The electrode will collect copper

What will happen if hydrogen is present?

Bubbles will form at the electrode

ammonium ion

NH4+

nitrate ion

NO3-

hydroxide ion

OH-

Sulfate ion

SO4 2-

Carbonate ion

CO3 2-

Nitric acid

HNO3

Sulfuric Acid

H2SO4