How are moles calculated using mass and molecular weight?

To determine the number of moles from a given mass and molecular weight, you divide the mass of the substance by its molecular weight. The concept behind this calculation is based on the relationship established by the formula:

Moles = Mass / Molecular Weight.

This means that by knowing the mass of a substance (in grams) and its molecular weight (in grams per mole), you can easily calculate the number of moles present. The molecular weight gives you the mass of one mole of that substance.

In this context, the correct formula is simplified to show that for every one mole of the substance, the molecular weight in grams corresponds to that quantity. Thus, when you have the mass and divide by the molecular weight, you effectively determine the number of moles present in that mass of the substance. The option that accurately reflects this relationship is:

moles = mass / molecular weight.

The correct answer follows this principle by rearranging the formula correctly, leading to the appropriate calculation method.