Question

How many total atoms are in 0.920 g of P2O5?

Answer 1

Molar mass P2O5 = 31 x 2 + 16 x 5 => 142 g/mol


142 g ---------------- 6.02 x 10²³ molecules
0.920g g ------------ ( molecules )

molecules = 0.920 x ( 6.02 x 10²³ ) / 142

molecules = 5.53 x 10²³ / 142

= 3.89 x 10²¹ molecules

1 molecule P2O5 -------------------------- 7 atoms
3.89 x 10²¹ molecules -------------------- ( atoms )

atoms = ( 3.89 x 10²¹) x 7 / 1

atoms = 2.72 x 10²² atoms of P2O5

hope this helps!

Answer 2

Given the mass of a compound, the total number of atoms can be determined by converting first the mass to moles and then multiplying the moles to Avogadro's number (6.022 x 10^23 atoms/mole). In this case, the answer is 3.9 x10^21 atoms