How much of a substance is contained in 140 calcium oxide?

Given:
m (CaO) = 140 g.

Find:
n (CaO) -?

Solution:
If we know the mass of a substance, then its amount can be found by the formula n = m / M (Where n is the amount of the substance, m is the mass of the substance, M is the molar mass of the substance).
Molar mass (M) of calcium oxide (CaO) = 140 g / mol.
Now we substitute the known to the formula for finding the amount of substance.
n (CaO) = 140 g / 140 g / mol.
n (CaO) = 1 mol.

Answer: n (CaO) = 1 mol.