Question

what is the mass in grams of 1.75*10 20 molecules of caffeine, C8H10N4O2 ?

Answer 1

C8H10N4O2 Molar mass = 194 g/mol

number of molecules = 1.75 x 10^20 molecules

1 mol caffine contain ----------------------> 6.023 x 10^23 molecules

       ??         --------------------->    1.75 x 10^20 molecules

number of moles of caffine = 1.75 x 10^20 x 1 / 6.023 x 10^23

                                       = 2.906 x 10^-4 moles

moles = mass / molar mass

2.906 x 10^-4 = mass / 194

mass of caffieine = 0.0564 g