What is formula mass and how is it calculated?

1 Answer
anor277
Jun 7, 2016

The formula mass of a molecule or species is simply the sum of the atomic masses of the constituent atoms in the formula of the compound.

Explanation:

The units of formula mass are thus #g*mol^-1#, or, more fundamentally, #"amu "=" atomic mass units"#. As chemists, we typically deal with molar quantities, so units of #g*mol^-1# are appropriate.

So let's try to calclate the formula mass of #Na_2SO_4# in #g*mol^-1#.

#"Formula mass " Na_2SO_4# #=# #(2xx22.99+32.06+4xx15.999)*g*mol^-1=??g*mol^-1#. From where did I get those numbers?

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