## Chemistry: Atoms First (2nd Edition)

Counting by weighing means weighing the whole sample and then dividing by the average mass of one unit. Imagine you have a bag of marbles. One marble weighs 50g and the whole bag weighs 5 kilos. Then, by dividing 5000 by 50, you can find the number of marbles easily. Since the numbers we are dealing with when counting molecules is extremely large, a new unit is defined to make counting easier. This unit is the mole, and it equals $6.022*10^{23}$