What is the mass (in grams) of 9.02 × 1024 molecules of methanol (ch3oh)?

You first calculate the formula mass of methanol (CH3OH). This is, add the mass of each element in the formula. C: 12 g/mol; H: 4* 1 g/mol = 4 g/mol; O: 16 g/mol => formula mass = 12 g/mol + 4g/mol + 16 g/mol = 32 g/mol. Second, calculate the number of moles in 9,02 * 10^24 molecules, using Avogadros number: number of moles = 9.02 * 10^24 molecules / 6.02 * 10^23 molecules/mol = 15 moles. Third, the mass in grams of the compound equals the number of moles times the formula mass = 15 moles * 32 g/mol = 480 g. 480 grams.