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