Question

What is the molecular weight of `H_3PO_4`?

Answer 1

If you take a look at a periodic table, let `Z` be the atomic number and `MM` be the molar mass of atom `X`:

`Z_"H" = 1`
`MM_"H" = 1.0079`

`Z_"P" = 15`
`MM_"P" = 30.974`

`Z_"O" = 8`
`MM_"O" = 15.999`

Just note how many of each atom is in the compound, and add accordingly. For instance, there are four oxygen atoms.

If you want to check your answer, just google the compound.