Question

calculate the ratio of atoms present in 5g of magnesium and 5g of iron

[atomic mass of Mg=24u,Fe=56u]

Answer 1

We are given that the atomic mass of Magnesium is 24 u. So the mass of 6.023 X 10²³ atoms of magnesium (that is molar mass of magnesium) is 24 g. Thus

24g of Mg = 6.023 X 10²³ atoms of Mg

or 1 g of Mg = (6.023 X 10²³ / 24) atoms of Mg

and 5 g of Mg = (6.023 X 10²³ X 5) / 24 atoms of Mg

= 1.255 X 10²³ atoms of Mg

As the atomic mass of iron is 56 u, so the mass of 6.023 X 10²³ atoms of iron (that is molar mass of iron) is 56 g. Thus

56g of Mg = 6.023 X 10²³ atoms of Fe

or 1 g of Fe = (6.023 X 10²³ / 56) atoms of Fe

and 5 g of Fe = (6.023 X 10²³ X 5 ) / 56 atoms of Fe

= 0.538 X 10²³ atoms of Fe

Therefore

Number of atom in 5 g of Mg / Number of atom in 5 g of Fe = 1.255 X 10²³ / 0.538 X 10²³

= 2.33