1. Moles and Chemical Formulae
Finding the Simplest Formula

2. Finding the Simplest Formula
Imagine you react g of Zn is reacted with excess Cl2(g)
When the Zn and Cl2 have finished reacting a white powder is left and has a mass of g
What is the formula for zinc chloride?

3. Finding the Simplest Formula
The simplest formula is obtained by dividing the number of moles of the elements by the smaller number of moles
Use whole numbers as subscripts to write the formula
Zn1Cl2 or ZnCl2

4. Magnesium Oxide Weigh crucible and cover Mcrucible
Weigh out g of Mg ribbon MMg
Tightly roll Mg and place in the crucible in the fume cupboard using the set-up on the right
With the lid off heat the crucible when the Mg ignites use crucible tongs to place lid on top of crucible
When there is no smoke, take off lid and heat for 5 more minutes
Let the crucible cool and add drops de-ionized water and heat gently to evaporate water, then heat strongly for another 4 mins
Allow to cool and weigh crucible and lid Mfinal

5. Formula of a Hydrate MgSO4.xH2O
Weigh crucible and cover Mcrucible
Fill the crucible 1/3 full the magnesium sulfate hydrate and with the lid on weigh it Mcrucible+hydrate
Heat gently using the set-up right for 5 mins
Heat strongly for 10 mins
Allow to cool and weigh crucible and lid Mfinal