gcsescience.com                                       17                                       gcsescience.com


Calculating the Empirical Formula from a Reaction.

Example 2.

20 g  of calcium was found to react with 35·5 g  of chlorine.
What is the empirical formula of calcium chloride?

1) Find how many moles of calcium
react with how many moles of chlorine.

RAM of Ca = 40RAM of Cl = 35·5.

moles = mass ÷ RAM

for calcium   moles = 20 ÷ 40
                              = 0·5 moles.

for chlorine   moles = 35·5 ÷ 35·5
                    = 1·0 moles.

2) The proportion of moles of calcium to moles of chlorine
is reduced to the lowest whole number.

0·5 moles of Ca to 1·0 moles of Cl.
Multiply by 2.
1 mole of Ca to 2 moles of Cl.
The empirical formula is CaCl2.

Since calcium chloride is an ionic compound,
the actual formula is the same as the empirical formula.

back      Links      Moles      Revision Quizzes      Revision Questions      next

gcsescience.com       The Periodic Table       Index       Moles Quiz       gcsescience.com

Home      GCSE Chemistry      GCSE Physics

Copyright © 2015 gcsescience.com. All Rights Reserved.