O Levels Chemistry Questions – Mole Calculations / Mole Concepts

In Chemistry, an equation represents what occurs in a chemical reaction:

LHS –> RHS
Reactants –> Product(s)

3 types:
• Word Equation
• Chemical Equation
• Ionic Equation

For Chemical Equation –> Using Chemical Formulae to represent a reaction known to take place.

Step 1: Write down the Chemical Formulae of reactant & products.

Na + Cl2 –> NaCl ——- Balanced???

Step 2: Check the number of atoms of each element on both sides.

Above equation is not balanced. An equation is balanced when there is equal number of atoms if each element on both sides of the equation.

Step 3: Balance the Equation.

The 4 RULES of balancing chemical equations:

• Start with balance of Group 1/2/Transition Metals
• Balance Non-metals atoms
• Balance all Oxygen atoms
• Balance Hydrogen atoms

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If you follow the steps above, you should be able to get the following balanced equation:
2Na + Cl2 –> 2NaCl

Step 4: Add the State Symbol

2Na (s) + Cl2 (g) –> 2NaCl (aq)

The balanced equation shows 2 atoms of sodium metal react with 1 molecule of chlorine gas to form 2 units of sodium chloride salt.

For state symbols, there are 4 types:
(s) solid state
(l) liquid state
(g ) gaseous state
(aq) aqueous state,dissolved in water

Hope you find this introduction to Mole Calculation useful to you.

Related Articles:

• O Level Chemistry – Determination of Ionic Equation & Spectator Ions
• Download your Fre-e Balancing of Chemical Equations Tips
• O Level Chemistry: Tips on assigning Oxidation Number (or States)
• O Level Chemistry: Mole Calculations – Balanced Chemical & Ionic Equations
• O Level Chemistry – Basicity of Acids