A sample of sulfur trioxide (SO3) weighs 5100 g. How many molecules are contained in this sample? Use 80.063gmol for the molar mass of SO3.

3.83 x 10^25 molecules

Explanation:

You first start off with 5100 grams. Then you use the molar mass to cancel out the grams and convert to moles (5100g / 80.063 gmol). You would then be left with 63.69 mols of SO3. But since it asks for molecules, you would need to multiply this value by Avogadro's number (6.022 X 10^23) in order to cancel out the mols unit and end in amount of molecules.