How many moles are in 25. mL of ethanol, C2H5OH (the density of ethanol is 0.785 g/mL)?
25.0 mL has a mass of 0.875*25.0 = 19.625 g. The molar mass of ethanol is 46.07 g/mol, so there are 19.625/46.07 = 0.426 moles
