Molar mass is used to convert moles to grams. If we look at 1 atom of carbon-1, it has a mass of 12 amu. 12 grams is equal to 1 mole of carbon-12, which has 6.02×1023 atoms. Thus, 1 mole of any element has a mass in grams that is numerically equivalent to its atomic mass.
For example, the atomic mass of hydrogen is 1.01 amu. This means that 1 mole of hydrogen is 1.01 g. Thus, the molar mass of hydrogen is 1.01 g/mole.
To get the molar mass for a compound, you add up all the molar masses of the atoms in the compound. For example, a water molecule is made up of 2 hydrogen atoms and 1 oxygen atom. To get the molar mass of water, you would add up the molar masses of 2 hydrogens (2 x 1.01 g) and 1 oxygen (1 x 16 g). The molar mass of water would then be 18.016 g/mole.
Example: If you had 7 g of nitrogen, how many moles of nitrogen do you have?
1) Figure out what the molar mass of nitrogen is.
Since the atomic mass of nitrogen is 14.01 amu, the molar mass of nitrogen is 14.01 g/mole.
2) Divide the amount of nitrogen you have by the molar mass.
(7 g) / (14.01 g/mole) = 0.4996 mole
Therefore, you have 0.4996 mole of nitrogen.
Example: If you had 3.4 moles of calcium, how many grams of calcium do you have?
1) Figure out what the molar mass of calcium is.
Since the atomic mass of calcium is 40.078 amu, the molar mass of calcium is 40.078 g/mole.
2) Multiply the number of moles of calcium you have by the molar mass.
(3.4 moles) x (40.078 g/mole) = 136.2652 g
Therefore, you have 136.2652 g of calcium.
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This article was written for you by Samantha, one of the tutors with SchoolTutoring Academy.