How many total atoms are in 0.830 g of p2o5?

First calculate moles of P2O5. moles = grams / molar mass

The molar mass for P2O5 = 2 x P (2 x 31.0) + 5 x O (5 x 16.0) = 142 g/mole.

0.760 g P2O5 x (1 mole P2O5 / 142 g P2O5) = 0.00535 moles P2O5

0.00535 moles P2O5 x (6.02 x 10^23 molecules P2O5 / 1 mole P2O5) = 3.22 x 10^21 molecules P2O5

Each molecule of P2O5 contains 2 P atoms and 5 O atoms (total = 7 atoms).

3.22 x 10^21 molecules P2O5 x (7 atoms / 1 molecule P2O5) = 2.25 x 10^22 atoms