The molar mass of Fe is 55.85 g/mol. A student needs 0.15 moles of Fe, so they should measure out ____ grams of Fe. Use 2 significant figures.

Answer 1

You can use dimensional analysis here to get the appropriate units. You are looking for an answer in grams. 55.85 g/mol * .15 mol cancels out the mol units and you are left with grams. 55.85*.15 = 8.38 grams

You could also think of this as a percentage. You need 15% of 1 mol which is 55.85g. 15% of 55.85 is 8.38 grams