# What is the molecular weight of H_3PO_4?

Nov 29, 2015

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

${Z}_{\text{H}} = 1$
$M {M}_{\text{H}} = 1.0079$

${Z}_{\text{P}} = 15$
$M {M}_{\text{P}} = 30.974$

${Z}_{\text{O}} = 8$
$M {M}_{\text{O}} = 15.999$

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