If your lab partner determined that there were 6.015 x 1021 atoms of O in an unknown sample of Mg(NO3)2

Question

how many milligrams would the unknown sample weigh? And could you please explain how you got the answer? Thank you in advance.

Answer 1

well if one measured 6.015 X 10^21 atoms of oxygen in the Mg(NO3)2 sample then that is equal to 6.015 X 10^21/6.023 X 10^23 atoms/mole

= 9.987 X 10^-3 moles = 9.987 mmol of O

the amount of O in Mg(NO3)2 is 6 mmole/mmole of Mg(NO3)2 , so 9.987 mmoles of O is 1.66mmol of Mg(NO3)2

= 1.66 X 151 mg /mmol = 250.66 mg