Answer
0.0500 mole of $SO_3$
Work Step by Step
1. Determine the molar mass of this compound ($SO_3$), and setup the conversion factors:
$S: 32.07g $
$O: 16.00g * 3= 48.00g $
32.07g + 48.00g = 80.07g
$ \frac{1 \space mole \space (SO_3)}{ 80.07 \space g \space (SO_3)}$ and $ \frac{ 80.07 \space g \space (SO_3)}{1 \space mole \space (SO_3)}$
2. Calculate the number of moles $(SO_3)$
$ 4.00g \times \frac{1 mole}{ 80.07g} = 0.0500$ $mole$
