A 40.0 mg packet of saccharin, C7H5NO3S, has a molar mass of 183.18 g/mol. How many saccharin molecules does it hold?

1. Convert the mass to grams first: 40.0 mg = 0.0400 g. 2. Find the amount in moles: 0.0400 g / 183.18 g/mol = 2.184 x 10^-4 mol. 3. Multiply by Avogadro's number: 2.184 x 10^-4 mol x 6.022 x 10^23 molecules/mol. 4. The product is 1.31 x 10^20 saccharin molecules. 5. Units cancel, since grams go in step two and moles go in step three. 6. The value 2.19 x 10^20 stops at the mole count and never applies Avogadro's number properly. 7. The value 9.17 x 10^20 is the count of carbon atoms, not of whole molecules. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.1 Formula Mass and the Mole Concept_