Calculating Reacting Masses

The slide show below shows how you can work out reacting masses in chemical equations.  The important thing to remember is that you need to have a correctly balanced equation (these will usually be given to you in an exam, you should also be given the atomic masses as part of the question, e.g. [Na = 23, O = 16], if not you will have to use the Periodic table at the back of the exam paper).  The clip is only 15 seconds long so pause it at each step and replay as often as you need.