How does one calculate the formula mass of a compound?

The formula mass of a compound is calculated by adding up the relative atomic masses of all the atoms in its formula.

To calculate the formula mass of a compound, you need to know the formula of the compound and the relative atomic masses of the elements that make up the compound. The relative atomic mass of an element is the average mass of one atom of an element compared to one twelfth of the mass of an atom of carbon-12. These values can be found on the periodic table.

Let's take an example. Suppose you want to calculate the formula mass of water, H2O. The formula tells you that there are two hydrogen atoms and one oxygen atom in each molecule of water. From the periodic table, you can find that the relative atomic mass of hydrogen is approximately 1, and the relative atomic mass of oxygen is approximately 16. So, the formula mass of water is (2 x 1) + 16 = 18.

For a more complex compound like calcium carbonate, CaCO3, you would do the same thing. The formula tells you that there is one calcium atom, one carbon atom, and three oxygen atoms in each molecule. From the periodic table, you can find that the relative atomic masses of calcium, carbon, and oxygen are approximately 40, 12, and 16, respectively. So, the formula mass of calcium carbonate is 40 + 12 + (3 x 16) = 100.

Remember, the formula mass of a compound is a measure of the average mass of one molecule of the compound, compared to one twelfth of the mass of an atom of carbon-12. It's a very useful concept in chemistry, because it allows you to work out how much of a particular compound you have if you know its mass, and vice versa.