Rubbing alcohol is 70% vol isopropanol. If isopropanol has density 0.785 g/mL, what mass is in a 355 mL bottle?

1. Volume percentage means the isopropanol volume is 70 percent of the total solution volume. 2. Find that volume: 355 mL x 70 mL isopropanol per 100 mL solution = 248.5 mL. 3. Convert the volume to a mass using the density of the alcohol itself. 4. That gives 248.5 mL x 0.785 g/mL. 5. The mass is 195 g of isopropyl alcohol. 6. The value 248 g reports the alcohol volume in millilitres with a gram label attached. 7. The value 279 g applies the density to the whole 355 mL rather than to the alcohol portion. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.4 Other Units for Solution Concentrations_