Molar mass means the mass of one mole. The molar mass concept can be applied to elements and to compounds. Molar mass is expressed in grams. For example, one mole of carbon has amass of 12 grams. Therefore, carbon’s molar mass is 12 grams. This is equivalent to the statement that 6. 02 x 1023 atoms of carbon have a mass of 12 grams. Consider this example: chemists know that one mole of aluminum has a mass of 27 grams. Therefore, they say the molar mass of aluminum is 27 grams. This is equivalent to the statement that 6. 02 x 1023 atoms of aluminum have a mass of 27 grams.
A compound is a chemical combination of atoms. Each compound has a fixed ratio of elements. Now, we apply the concept of molar mass to compounds as we did to elements.
– The molar mass of a compound is the sum of the molar masses of all of the atoms which make up the compound.
For example, the molar mass of H2O is 18 grams since chemists know that the molar mass of hydrogen is 1 gram and that the molar mass of oxygen is 16 grams. In other words, the two hydrogens in water have a total molar mass of 2 grams which is added to the molar mass of oxygen which is 16 grams. Therefore the molar mass of the whole compound is 18 grams.
