CHEMICAL FORMULAE AND EQUATIONS SUMMARY NOTES

CHEMICAL FORMULAE AND EQUATIONS

The formulae of compounds are written from the name of ions of atoms and the charge on the ions of atoms combined together.

There are two ways of writing the formulae of compounds:

1. Prefix method
   

   Prefixes are used to indicate the number of atoms present in a compound.
   

• Mono- = 1
  
• Di- = 2
  
• Tri- = 3
  
• Tetra- = 4
  

  Examples
  

  Carbon monoxide (CO)
  

  Carbon dioxide (CO₂)
  

  Sulphur dioxide (SO₂)
  

  Sulphur trioxide (SO₃)
  

  Dinitrogen monoxide (
  

  Dinitrogen pent oxide (
  

   

   

   

   

   

   

   

   

   

   

1. Valency method
   

   This is when valences of atoms, ions or radicals (compound ions) are used to determine the proportions of atoms in a compound.
   

    

   Negative ions (anions)
   

    

Positive ions (cations)

Polyatomic ions/compound ions/radicals

Examples

Write the formula of the following compounds

1. Sodium hydroxide
   
2. Calcium oxide
   
3. Aluminium oxide
   
4. Magnesium nitrate
   
5. Potassium phosphate
   
6. Ammonium carbonate
   
7. Copper II chloride
   

Exercise

Write the formula of the following compounds

1. Manganese IV oxide
   
2. Calcium phosphate
   
3. Copper II sulphate
   
4. Magnesium sulphite
   
5. Lead II nitrate
   
6. Sodium phosphate
   
7. Iron III phosphate
   
8. Magnesium hydrogen carbonate
   
9. aluminium sulphate
   
10. zinc hydroxide
    
11. ammonium sulphate
    
12. lithium oxide
    

EQUATIONS

There are two parts to an equation, which are reactants and products. The two are separated by an arrow. Reactants are found on the left hand side and products on the right hand side

There are two ways to write equations of chemical reactions.

1. Word equations
   

   A word equation is written in words
   

   Examples
   

   1. Sodium chloride + magnesium nitrate → sodium nitrate + magnesium chloride
      
   2. Calcium phosphate + aluminium sulphate →
      
   3. Potassium fluoride + sodium carbonate →
      
   4. Lead ii chloride + potassium iodide →
      
   5. Ammonium hydroxide + copper II sulphate →
      
   6. Zinc chloride + sodium hydroxide →
      

       

2. Symbolic equations
   

   These are equations where symbols or formulas of compounds are used.
   

   Examples
   

   Rewrite the following word equations as symbolic equations.
   

    

    

    

    

    

    

    

    

    

    

   BALANCING OF EQUATIONS
   

   Rules for balancing equations
   

   1. Count the atoms on each side of the equation
      
   2. If the number of each type of an atom on either side of the equation is not the same, we have to balance the equation.
      
   3. In balancing of equations put big numbers at the back of the formula which contains atoms that do not balance.
      
   4. Carry on until the atoms on each side of the equation are the same
      

      NB: Only symbolic equations could be balanced.
      

       

       

      Common acids
      

      Hydrochloric acid HCl
      

      Sulphuric acid H₂SO₄
      

      Nitric acid HNO₃
      

      Carbonic acid H₂CO₃
      

      Phosphoric acid H₃PO₄
      

       

       

       

       

      Common di-atomic molecules
      

       

• Hydrogen H₂
  
• Oxygen O₂
  
• Nitrogen N₂
  
• Chlorine Cl₂
  
• Fluorine F₂
  
• Bromine Br₂
  
• Iodine I₂
  

   

   

  Examples
  

  Balance the following equations
  

Ionic equations

These are equations which show the ions which take part in a chemical reaction.

Ions which do not take part in a chemical reaction are called SPECTATOR IONS.

SOLUBILTY RULES

1. All acids are soluble
   
2. All nitrates are soluble
   
3. All sulphates are soluble EXCEPT BaSO₄, CaSO₄, PbSO₄
   
4. All chlorides, Iodides, Bromides are soluble except for silver, lead and mercury.
   
5. All carbonates are INSOLUBLE except those formed by group 1 elements and ammonium carbonate, (NH₄)₂CO₃.
   
6. All hydroxides and oxides are insoluble except those formed by group 1 elements and ammonium.
   

    

   NB: All ammonium compounds are soluble
   

   All compounds formed by group 1 are soluble
   

    

   HOW TO WRITE AN IONIC EQUATION
   

    

   1. Write a balanced chemical equation
      
   2. Put state symbol into the equation
      
   3. Break down/separate the aqueous substances into ions. PLEASE DO NOT BREAK DOWN, SOLIDS, LIQUIDS AND GASES.
      
   4. Cancel out those ions which appear on both sides of the equation (spectator ions)
      
   5. What remains is the net ionic equation
      

       

      Examples