The key to answering any moles calculation question in chemistry is working out which equation you need to use. Generally, if moles are involved it will be moles = volume x concentration or moles = mass/RFM. You should look at what measurements are mentioned in the question information and determine which of these equations should be used. Then, rearrange the equation with the two parameters you have been given so that you can calculate the unknown. Finally, you should make sure you have used the correct units and that you have considered the mole ratio between the two sides of the equation . Using the mole ratio allows you to calculate values for any of the compounds in an equation if you can work out the moles of just one of the compounds.