How many molecules are there in 7.58 mg of carbon tetrachloride?

Answer 1

First responder has the right idea but used the wrong mass for chlorine (as well as making an arithmetic error). The correct molecular mass is 12 + 35.5x4 = 154. So 7.58E-3 grams of carbon tet is 4.92E-5 moles, or 2.965E19 molecules.

Answer 2

CCl4

One mole = 12 + 4*17 = 80

7.58 mg / 80 g/mol * g/1000 mg = 9.5E-5 moles

9.5E-5 moles * 6.02E23 molec/mole = 5.7E18 molecules