Calculate number of atoms in 120 g of calcium and 120 g of iron. Which one has more number of atoms and how much is the difference ? (Given atomic mass of calcium - 40 u and iron = 56 u)


#1

40 g of Ca = 1 mol
120 g = 120/40 = 3 mol
1 mol contains 6.022 x 10^23 atoms

Therefore,
3 mol contains 3 x 6.022 x 10^23 Ca atom
= 18.066 x 10^23 Ca atoms

56 g of Fe = 1 mol
120 g of Fe = 120/56 = 2.14 mol

1 mol contains 6.022 x 10^23 atoms
2.14 mol = 2.14 x 6.022 x 10^23 atoms
= 12.887 x 10^23 Fe atoms

Calcium has more no. of atoms.
Difference = 5.179 x 10^23 atoms