This is a hierarchy, as in Figure 2, but with the actual chemistry tricky topic moles represented. At the top is the tricky topic moles. Below and linked to the moles tricky topic are four stumbling blocks labelled ‘What is a mole?’, ‘Purpose of moles’, ‘Knowledge of atoms’ and ‘Working with equations’. Underneath these stumbling blocks, and linked to them, are five student problem examples such as ‘Converting units and using them appropriately’. This example student problem is linked to the stumbling block, ‘working with equations’. Another student problem example is, Unable to visualize a mole and grasp concept. This student problem example is linked to two stumbling blocks, stumbling block 1, What is a mole, and stumbling block 2, Purpose of moles.