What is the mass of exactly 500 molecules of chloral hydrate?

Chloral hydrate has the formula C2H3Cl3O2

mass of carbon : 12

mass of Cl : 35.5

mass of hydrogen : 1

mass of oxygen : 16

So, molar mass of chloral hydrate = 2 (12) + 3 (1) + 3 (35.5) + 2 (16) = 165.5 gm

1 mole contains 6.02 x 10^23 molecules

Thus, mass of one molecule = 165,5 / (6.02 x 10^23) = 2.75 x 10^-22 gm

therefore, mass of 500 molecules is equal to:

500 x 2.75 x 10^-22 = 1.37 x 10^-19 gm