Question

How do you find formula mass?

Answer 1

Got a Periodic Table handy?

Explanation:

Consider the formula, and sum up the masses of each element in the formula to give the formula mass. You get an answer in `g*mol^-1, "a mass in gram per Avogadro's number of atoms"`.

So let's take an example: `OsO_4` (I don't know why I chose that one!). In `1` `mol` of this stuff, there are `1` `mol` metal atoms, and `4` `mol` of `O` atoms. I take the masses from the Periodic Table, and I get a mass of `{190.23(Os)+4xx15.999(O)}*g*mol^-1=254.23 *g*mol^-1`.

You can of course do this with any given formula. You will have access to a Periodic Table in any Chemistry or Physics examination.