What is the formula weight?

1 Answer
anor277
Dec 13, 2016

This is simply a calculation of the mass of one mole of a given substance.

Explanation:

Let's take a random formula, #CaCO_3#.

1 mole of calcium has a mass of #40.1*g#; 1 mole of carbon has a mass of #12.01*g#; 3 mole of oxygen has a mass of #3xx15.999*g#. Sum them together, and we get a so-called #"formula mass"# of #100.12*g*mol^-1# (i.e. units are #g*mol^-1# or #g*("Avogadro's Number")^-1# of reagent).

From where did I get the atomic masses? Did I know them from memory? (In fact I did, and you'll get to know the common ones very rapidly.) This operation is something that you will do routinely and rapidly.

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