To determine how many moles of a substance exist, what do you need to know first?

To determine how many moles of a substance exist, knowing the mass of the substance and its relative formula mass is essential. The mass provides the total quantity of the substance you have, while the relative formula mass informs you of the mass of one mole of that substance. By using the equation:

[ \text{Number of moles} = \frac{\text{mass of the substance}}{\text{relative formula mass}} ]

you can accurately calculate the number of moles present. This process relies on both pieces of information to derive the moles effectively.

Other factors such as the physical state, temperature, volume, and pressure may be relevant in different contexts of chemistry, like gas laws or state-specific calculations, but they do not directly contribute to determining the number of moles in the straightforward manner that mass and relative formula mass do. For quantitative analysis of moles, the focus should remain on mass and relative formula mass.