Question

How many total atoms are in 0.210 g of P2O5?

Answer 1

Molar mass of P2O5,

MM = 2*MM(P) + 5*MM(O)

= 2*30.97 + 5*16.0

= 141.94 g/mol

mass(P2O5)= 0.210 g

use:

number of mol of P2O5,

n = mass of P2O5/molar mass of P2O5

=(0.21 g)/(1.419*10^2 g/mol)

= 1.479*10^-3 mol

use:

number of molecules = number of mol * Avogadro’s number

number of molecules = 1.479*10^-3 * 6.022*10^23 molecules

number of molecules = 8.91*10^20 molecules

Count of each element in compound is:

{P=2, O=5}

Total number of atoms in 1 molecule = 7

use:

number of atoms = number of molecules * Total number of atoms in 1 molecule

number of atoms = 8.91*10^20 * 7

number of atoms = 6.237*10^21

Answer: 6.24*10^21