Empirical formula example (Edexcel GCSE Chemistry): Revision Notes

Empirical formula example

Finding the Empirical Formula

	Mg	Cl
Mass (g)	1.92	5.68
Relative Atomic Mass (Ar)	24	35.5
Moles	$\frac{1.92}{24}​=0.08 moles$	$\frac{5.68}{35.5} =0.16 moles$
Simplify Ratio	$\frac{0.08}{0.08} ​=1$	$\frac{0.16}{0.08} ​=2$

Step-by-Step Explanation

1. Mass of Elements:

• Magnesium ($Mg$): 1.92 g
• Chlorine ($Cl$): 5.68 g

2. Relative Atomic Masses (Ar):

• $Mg$ = 24
• $Cl$ = 35.5

3. Calculate Moles: Moles of $Mg$ =

$$\frac{1.92}{24} = :highlight[0.08]$$

Moles of $Cl$ =

$$\frac{5.68}{35.5} = :highlight[0.16]$$

4. Simplify the Ratio: Divide each by the smallest number of moles (0.08):

• $Mg$:

$$\frac{0.08}{0.08} = :success[1]$$

• $Cl$:

$$\frac{0.16}{0.08} = :success[2]$$

5. Empirical Formula: The simplest whole-number ratio is 1:2, so the empirical formula is $MgCl2_22.$