How do you find formula mass?

1 Answer
anor277
Jun 28, 2016

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.

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