What is the mass of 7.24 x 1023 molecules of barium oxide?

Question

What is the mass of 7.24 X 10 (23rd power) molecules of barium oxide?

Hoping someone can let me know if I did this right:
I added Ba (137.3) and O (16.00) together and got 153.3

I then multiplied 153.3 to 7.24 for an answer of
1109.90 x 10 (23rd power).

This just doesn't look right though; did I miss a step?

Answer 1

When you have molecules and you need to convert to grams, you have to first convert the molecules to moles (use Avogadros #, 6.022 x 10^23) and then convert from moles to grams using the atomic mass (the 153.3 g). The units should cancel when you do the dimensional analysis. Hope this helps!

Answer 2

Always start with the given problem. Your given is the number of molecules. Divide 7.24x10^23 molecules by Avogadro's number, which is 6.02x10^23 molecues. The answer equals to 1 mole of BaO. You multiply the answer with the molar mass (153.3g). That's your answer.