Chemistry IGCSE

Relative atomic mass (A_r) of an element equation

A_r = (atomic mass of 1st isotope × its % abundance) + (atomic mass of 2nd isotope × its % abundance) + … and so on.

Percentage composition of a compound equation

$$\frac{\text{relative atomic mass}}{\text{relative molecular or formula mass}}\times100=_{}\%$$

Percentage purity of a substance equation

$$\frac{\text{mass of pure substance in it}}{\text{total mass}}\times100=\%_{}$$

Molar mass equation

___ mol (+ chemical formula) × relative atomic/formula/molecular mass = ___ g

Number of molecules equation

___ mol (+ chemical formula) × 6.02 × 10²³ = ___ molecules

Volume of a gas equation

___ mol (+ chemical formula) × 24dm³ = ___ dm³

Concentration equation

$$\frac{amountofsolute\left(mol_{}\right)}{\text{volume of solution (dm³)}}=concentration\left(\frac{mol}{dm^{3}}\right)$$

Percentage yield equation

actual mass of product obtained / theoretical mass of product × 100 = ___ %

K+

Potassium

Na+

Sodium

Ca2+

Calcium

Mg2+

Magnesium

Al3+

Aluminium

C

Carbon

Zn2+

Zinc

Fe2+ or Fe3+

Iron

Sn2+

Tin / Stanum

Pb2+

Lead

H+

Hydrogen

Cu2+

Copper

Ag+

Silver

Au+

Gold

Enthalpy change equation

Enthalpy change for the reaction (∆H; in kJ/mol) = energy in for bond breaking - energy out from bond making.

Positive enthalpy change

Endothermic reaction

Negative enthalpy change

Exothermic reaction

Rate

A measure of the change that happens in a single unit of time.

the amount of reactant used up OR product produced per unit of time.

To find the rate of a reaction, measure:

increase concentration, temperature, surface area, pressure (gases only), add catalysts.

To increase rate

Catalyst

A substance that increases the rate of a reaction and is unchanged at the end.

hydrogen peroxide → water + oxygen

Decomposition of hydrogen peroxide 2H₂O₂ (l)

Reversible reaction

The direction of the reaction (forward and reverse) can be changed by changing the reaction conditions.

Dynamic equilibrium

When the forward and reverse reactions take place at the same rate & the concentrations of reactants and products are no longer changing in a reversible reaction in a closed system.

blue; white powder

Hydrated CuSO₄ and anhydrous CuSO₄ colors

pink; blue powder

Hydrated CoCl₂; anhydrous CoCl₂ colors

Haber process

N₂ + 3H₂ ⇌ 2NH₃

200 atm/20,000kPa, constantly removed, 450C, iron

Haber process conditions (pressure, ammonia, temperature, catalyst)

nitrogen from air, hydrogen from reacting natural gas (methane) + steam OR cracking hydrocarbons from petroleum

Haber process source of reactants

Contact process

2SO₂ (g) + O₂ (g) ⇌ 2SO₃ (g)

2 atm/200 kPa, constantly removed, 450C, vanadium (V) oxide

Contact process conditions (pressure, sulfur trioxide, temperature, catalyst)

Sulfur mined OR sulfur dioxide from metal sulfide ores roasted in air.

Contact process source of reactants

exothermic

Haber and Contact process reaction type

Redox reactions

Oxidation and reduction always happen together.

Oxidation/oxidised

Gain of oxygen or loss of electrons.

Reduction/reduced

Loss of oxygen or gain of electrons.

Oxidation number

Shows how many electrons each atom of an element has lost/gained/shared in forming a compound.

Oxidising agent

A substance that undergoes reduction and oxidises the other substance (potassium manganate etc).

Reducing agent

A substance that undergoes oxidation and reduces the other substance (potassium iodide etc).

Bases

Have a pH > 7 and are oxides/hydroxides of metals (OH–).

Alkali

A type of base that is soluble in water.

Calcium hydroxide Ca(OH)₂ (aq), sodium hydroxide NaOH (aq), potassium hydroxide KOH (aq)

Strong alkalis include

Acids

Have a pH < 7 and have H+ ions.

Sulfuric acid H₂SO₄ (aq), hydrochloric acid HCl (aq), nitric acid HNO₃ (aq)

Strong acids include

Strong vs weak acids

Strong/weak acids dissociate completely/partially in water to produce a high/low concentration of H+ ions.

red/blue litmus paper, methyl orange, thymolphthalein, universal indicator, pH meter

pH indicators include

salt + water

Acid + alkali →

salt + hydrogen gas

Acid + metal →

salt + water

Acid + metal oxide →

salt + carbon dioxide + water

Acid + metal carbonate →

Ethanoic acid CH₃COOH (aq)

One weak acid is

salt + ammonia gas + water

Base +  Ammonium salt → 

H⁺ (aq) + OH^- (aq) → H₂O (l)

Water equation

Titration

A process used to find the unknown concentration of an acid/alkali through precise neutralisation.

Spectator ions

Ions which are not involved in the reaction.

donors, acceptors

Acids are proton __. Bases are proton __.

Oxides

Compounds containing oxygen and another element.

Basic metal oxides

From metals of Group I & II (CuO, CaO, etc).

Amphoteric metal oxides

From metals of Group III and zinc (Al₂O₃ and ZnO); they will react with acids and alkalis.

Acidic oxides

From elements of Group IV, V, VI, and VII (SO₂, CO₂, etc).