Chemical Changes

Oxidation

Gain of oxygen, loss of electrons

Reduction

loss of oxygen, gain of electrons

Reactivity series of metals

The series shows the metals in order of their reactivity.

Reactivity of metals with acids

Metals above H2 in reactivity series react with acid to produce H2. The more reactive the metal is, the quicker and more violent reaction with acid occurs. Metals below H2 don't react with acids.

Reactivity of metals with water

Not all metals above H2 react with water - mostly Group I and II metals. Aluminium is the borderline case.

Displacement reaction

A reaction where a more reactive metal displaces a less reactive metal from a compound.

Unreactive metals in Earth

In their natural state (well, they are unreactive...).

Extraction of metals less reactive than carbon

Reduction with carbon. Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure metal.

Extraction of metals more reactive than carbon

By electrolysis.

General equation for a reaction between metals and acids

Metal + acid → salt + hydrogen.

Type of reaction between metals and acids

Redox reaction, also a displacement reaction.

Metals that react with acid

Those above hydrogen.

General equation for a neutralisation reaction

Base + acid → salt + water.

General equation for the reaction between metal carbonate and acid

Metal carbonate + acid → salt + water + carbon dioxide.

General equation for the reaction between metal oxides and acids

Metal oxide + acid → a salt + water.

Redox reaction

A reaction involving both oxidation and reduction.

Oxidation-Reduction Reaction

A reaction where both oxidation and reduction occurs.

Oxidation in Magnesium Reaction

Magnesium has lost electrons and thus has been oxidised (Mg to Mg2+).

Reduction in Magnesium Reaction

The hydrogen in HCl has gained electrons and thus has been reduced (H+ to H2).

Formation of Soluble Salt

React the excess acid with some insoluble chemical (e.g. metal oxide), filter off the leftovers, crystallise the product.

Products of Acids and Alkalis

Acids produce hydrogen ions, alkalis produce hydroxide ions.

Definition of Bases, Acids, and Alkalis

Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions.

pH Scale

The measure of acidity/alkalinity of a solution; neutral solution.

Neutralisation Reaction Equation

H+ + OH− → H2O.

Strong Acid

Strong acid is completely ionised in aqueous solution.

Weak Acid

Weak acid is only partially ionised in aqueous solution.

Effect of H+ Concentration on pH

The pH decreases as concentration of H+ increases.

Concentrated Acid

Concentrated acid has more moles of acid per unit volume than dilute.

Dilute Acid

Dilute refers to solutions of low concentrations.

Concentration vs Strength of Acid

Concentration is not the same thing as strength of an acid; strength refers to whether the acid is completely ionised in water (strong) or only partially (weak).

Change in H+ Concentration with pH

As the pH is decreased by one unit, the hydrogen ion concentration increases by a factor of 10.

Increases by a factor of 10

Higher tier only

LiNO3

Lithium nitrate

K2CO3

Potassium carbonate

MgBr2

Magnesium bromide

BaSO4

Barium sulfate

What is electrolysis?

The passing of an electric current through ionic substances that are molten or in solution to break them down into elements; ions are discharged (they lose/gain electrons) at electrodes to produce these.

What is an electrolyte?

The liquid/solution which conducts electricity.

What is a cathode and what is an anode?

Cathode is the negative electrode, anode is the positive electrode.

What occurs at the cathode and what occurs at the anode during electrolysis?

Reduction occurs at the cathode. Oxidation occurs at the anode.

In aqueous electrolysis, which element is discharged at the cathode?

The less reactive element discharges at the cathode. Hydrogen is produced unless there is a less reactive metal, in which case the said metal is produced. Oxygen is produced at the anode unless the solution contains halide ions, in which case halogen molecules are produced.

How is aluminium manufactured?

Aluminium is made through the electrolysis of aluminium oxide and cryolite. Lots of energy is needed to produce the current in electrolysis which makes this process expensive.

What are the half equations in the extraction of aluminium?

Al3+ + 3 e− → Al (cathode). 2 O2− → O2 + 4 e− (anode). Oxygen reacts with C of the anode producing CO2.

Why is cryolite used in this process?

It lowers the melting point of aluminium oxide, reducing energy costs.

What are the half equations in electrolysis of the aqueous Na2SO4?

2 H+ + 2 e− → H2 (cathode). 4 OH− → 2 H2O + O2 + 4 e− (anode).

What are the half equations in electrolysis of the molten and aqueous KCl?

K+ + e− → K (cathode). 2 Cl− → Cl2 + 2 e− (anode). 2 H+ + 2 e− → H2 (cathode). 2 Cl− → Cl2 + 2 e− (anode), respectively.

What are the half equations in electrolysis of the aqueous CuBr2?

Cu2+ + 2 e− → Cu (cathode). 2 Br− → Br2 + 2 e− (anode).