Make sure to check for sig figs though. Basically, you have 2.54 mL and you multiply that by the 0.789 g/mL and mL cancels out and you are left with 2.00406g. There are 46.06844 grams per mol of ethanol, so to cancel out grams we multiply by 1/46.06844. And then we are left with 0.04350179862 mol
