Knowing either the empirical or molecular formula of a compound, can help to determine its composition in more detail. The opposite is also true. Knowing the composition of a substance can help you to determine its formula. There are four different types of composition problems that you might come across:
Problems where you will be given the formula of the substance and asked to calculate the percentage by massof each element in the substance.
Problems where you will be given the percentage composition and asked to calculate the formula.
Problems where you will be given the products of a chemical reaction and asked to calculate the formula of one of the reactants. These are often referred to as combustion analysis problems.
Problems where you will be asked to find number of moles of waters of crystallisation.
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