converting molecules to mass?

Question

Calculate the mass of 1.45 1024 molecules of N2O5. Use a molar mass with at least as many significant figures as the data given.

Answer 1

a mole is 6.022×10^23 particles.
(1.45 * (10^24)) / (6.02200 * (10^23)) = 2.41 moles

N = 14 atomic mass
O = 16

(14 * 2) + (16 * 5) = 108 g/mole
(2.41 mole) * 108 (g / mole) = 260.28 grams

Answer 2

Aaahh, Avogadro's number is used in this instant. I know just because of the units, but the x 10^23 is another good sign. I'm too tired to do math, so I'll just give you the conversions. 19.8 * 10^23 molecules x 1 mol/(6.22 * 10^23) x 342.2979 g/1 mol = whatever (in g)

Answer 3

use Avagadro's number: 6.02 X 10^23

this is the number of molecules per mole.

a mole of something weighs the atomic number but in grams....

for example the atomic number of oxygen is 16 so 1 mole of oxygen weighs 16 grams.

This should be enough info to get you where you want to go.

Good Luck.