Question: how many molecules of sio2 are there in a single grain of sand?
Answer: Using the bottom end of the mass range, a grain of sand has a mass of 0.67 mg or 6.7*10 -4 grams. Divide 6.7*10 -4 by 60.08 and we find that we have 1.1*10 -5 moles of SiO2. Multiplying that by the number of particles per mole and we get 6.7*10 18 molecules of SiO2.