WJEC AS Chemistry Unit 1.1 - Equations and Formulae

Formula for Water

H₂O

Formula for Carbon Dioxide

CO₂

Formula for Sulfur Dioxide

SO₂

Formula for Methane

CH₄

Formula for Hydrochloric Acid

HCl

Formula for Sulfuric Acid

H₂SO₄

Formula for Nitric Acid

HNO₃

Formula for Ethanoic Acid

CH₃CO₂H

Formula for Ammonia

NH₃

Formula for Ammonium Chloride

NH₄Cl

Formula for Sodium Hydroxide

NaOH

Formula for Sodium Chloride

NaCl

Formula for Sodium Carbonate

Na₂CO₃

Formula for Sodium Hydrogencarbonate

NaHCO₃

Formula for Sodium Sulphate

Na₂SO₄

Formula for Copper (II) Oxide

CuO

Formula for Copper (II) Sulphate

CuSO₄

Formula for Calcium Hydroxide

Ca(OH)₂

Formula for Calcium Carbonate

CaCO₃

Formula for Calcium Chloride

CaCl₂

Formula for an Ammonium Ion

NH₄⁺

Formula for a Hydrogen Ion

H⁺

Formula for a Lithium Ion

Li⁺

Formula for a Potassium Ion

K⁺

Formula for a Sodium Ion

Na⁺

Formula for a Silver Ion

Ag⁺

Formula for a Barium Ion

Ba²⁺

Formula for a Calcium Ion

Ca²⁺

Formula for a Magnesium Ion

Mg²⁺

Formula for a Copper (II) Ion

Cu²⁺

Formula for an Iron (II) Ion

Fe²⁺

Formula for an Iron (III) Ion

Fe³⁺

Formula for an Aluminium Ion

Al³⁺

Formula for a Bromide Ion

Br^-

Formula for a Chloride Ion

Cl^-

Formula for a Fluoride Ion

F^-

Formula for an Iodide Ion

I^-

Formula for a Hydrogencarbonate Ion

HCO₃^-

Formula for a Hydroxide Ion

OH^-

Formula for a Nitrate Ion

NO₃^-

Formula for an Oxide Ion

O^2-

Formula for a Sulfide Ion

S^2-

Formula for a Carbonate Ion

CO₃^2-

Formula for a Sulfate Ion

SO₄^2-

Formula for a Phosphate Ion

PO₄^3-

Writing the formula for ionic compounds

1. Write the symbols of the ions in the compound

2. Balance the ions so that the total of the positive ions and negative ions adds to zero (the compound itself must be neutral)

3. Write the formula without the charges and put the number of ions of each element as a small number following and below the element symbol

Oxidation numbers

• the number of electrons that need to be added to (or taken away from) an element to make it neutral

• Used in redox reactions to show which species is oxidised and which is reduced; increases = oxidised, decreases = reduced

• Used to name compounds unambiguously

Writing balanced chemical equations

1. Write a word equation for the reaction (optional)

2. Write the symbols and formulae for the reactants and products (make sure that all formulae are correct)

3. Balance the equation by multiplying formulae if necessary (never change a formula)

4. Check to see if the equation is balanced

5. Add state symbols (if required)

   • (s) = solid

   • (g) = gas

   • (l) = liquid

   • (aq) = aqueous (solution in water)

Writing ionic equations

• Frequently used for displacement and precipitation reactions

  1. Write out the chemical equation

  2. Write out the same chemical equation but using the ions

  3. Write out the ionic equation using the ions that are changed, leave out the unchanged spectator ions

Stoichiometry

The molar relationship/ratio between the amounts of reactants and products in a chemical reaction