Calcium hydroxide has a molar mass of 74 grams per mole. This can be determined by looking at its molecular formula of Ca(OH)2 and adding together the atomic weights of each individual atom. The atomic weights of the individual atoms are found on the periodic table.
Calcium hydroxide is composed of one calcium atom, two oxygen atoms and two hydrogen atoms. The molar mass of calcium is 40 grams/mole, the molar mass of oxygen is 16 grams/mole and the molar mass of hydrogen is 1 gram/mole.
A student must add all of these masses together to find the molar mass of calcium hydroxide, but also remember that there are two moles of oxygen and two moles of hydrogen in the compound.
The addition expression for the molar mass of calcium hydroxide is 40 grams/mole + 16 grams/mole + 16 grams/mole + 1 gram/mole + 1 gram/mole. The final product is 74 grams/mole, which is the molar mass of the compound.
The molar mass of any compound can be found this way. Students computing the molar masses of chemical compounds must know the structural formula of the compound and have access to a periodic table. They can also be given the molar masses of the individual atoms.