What does one mole of oxygen atoms represent?
This is why educators go to such lengths to teach the mole. It is the link between the micro world of atoms and molecules, to the macro world of grams, and kilograms, and litres. For a given substance, if I know its identity AND its mass, I can estimate how many individual particles that mass contains.
And thus we can introduce the idea of chemical equivalence. Write the equation, and show the molar equivalence, we can find the required number of reacting particles, just by measuring their mass or volume.
See this older answer and links for more of the same spray.