What is formula mass and how is it calculated?

Answer 1

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.

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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Answer 2

Wyatt Atkins

Formula mass is the sum of the atomic masses of all the atoms in a chemical formula. It is calculated by multiplying the atomic mass of each element in the formula by the number of atoms of that element, then adding up the results for all elements in the formula.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.