Question

How many total atoms are in 0.690 g of P2O5?

Answer 1

M P₂O₅ = 31g×2 + 16g×5 = 142g/mol

1 mole of P₂O₅ contains 5 moles of atoms
5 moles of atoms = 30,01×10²³ a.

142g ----------- 30,01×10²³ a.
0,69g ---------- X
X = (0,69×30,01×10²³)/142
X = 0,14626×10²³ = 1,4626×10²² atoms

:)