The two dot points listed under the first "perform simple calculations" heading are molar mass and percentage composition, neither of which are particularly hard. Hopefully I don't end up overcomplicating this as I tend to overcomplicate everything.
Molar Mass
Molar mass is simple. Just add up the mass numbers of all of the atoms in the chemical formula, as I wrote in my post Formula Weights and Molecular Weights. (Mind you, I'm not entirely sure about the terminology, so I might have to revise that, but rest assured that I know the concepts, or at least I think I do. I'm learning too...)
Percentage Composition
Percentage composition is the next step. It's basically what % of the mass of a compound is element X, what % is element Y (Ooh. Yttrium. Or not.), and so on. It's really easy to work out the percentage composition. Just get the mass of element X and divide it by the total mass to get the % of X by mass. Then repeat for all of the elements.
For example, let's say you're trying to work out the percentage composition of water.
The molar mass of water is 18.016 (each H has a mass number of 1.008 and oxygen has a mass number of 16).
% H = (1.008 x 2) / 18.016 = 11.19% (2 d.p.)
% O = 16 / 18.016 = 88.81% (2 d.p.)
One way to check your answer is to add up the percentages. If they don't add up to 100%, you've made an error somewhere.
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