# How many moles does 0.225 g of oxygen atoms represent?

## Question:

How many moles does 0.225 g of oxygen atoms represent?

## Calculating moles from grams

Conversion of grams to moles is a calculation that is done often in chemistry. If one is given mass, it is necessary to utilize the periodic table to find moles. The atomic masses given on the periodic table can be interpreted in two ways: It is the mass of a single atom of the element in atomic mass units (amu) or it is the mass of one mole of atoms of the element in grams. Using the atomic masses on the periodic table, one can easily convert any given mass of an element or compound into moles:

{eq}\textrm{moles} = \frac{\textrm{mass in grams|}}{\textrm{molar mass in grams}} {/eq}

Conversion of mass of oxygen to moles requires the atomic mass of oxygen from the periodic table. The atomic mass of oxygen is {eq}16.0\frac{g}{mol} {/eq} to three significant figures. We can calculate the moles of oxygen in the given amount of grams as follows:

{eq}0.225\;g \; O \left(\frac{1\;mol\;O}{16.0\;g \;O}\right)=0.0141\;mol \;O {/eq}

This calculation is written in this way to show how the units cancel. The overall effect is dividing the mass of oxygen atoms by the mass of one mole of oxygen atoms. 