Given :
Mass of urea = 5.6 g
To find :
The number of atoms of hydrogen, nitrogen, carbon and oxygen
Calculation :
Molecular formula of urea :
(NH2)2CO
Molar mass of urea = 60 g mol-1
Number of moles = \(\frac{Mass\,of\,a\,substance}{Molar\,mass\,of\,a\,substance}\)
= \(\frac{5.6\,g}{60\,g\,mol^{-1}}\)
= 0.0933 mol
∴ Moles of urea = 0.0933 mol
Number of atoms = Number of moles × Avogadro’s constant
Now,
1 molecule of urea has total 8 atoms, out of which 4 atoms are of H, 2 atoms are of N, 1 of C and 1 of O.
∴ Number of H atoms in 5.6 g of urea = (4 × 0.0933) mol × 6.022 × 1023 atoms/mol
= 2.247 × 1023 atoms of hydrogen
∴ Number of N atoms in 5.6 g of urea = (2 × 0.0933) mol × 6.022 × 1023 atoms/mol
= 1.124 × 1023 atoms of nitrogen
∴ Number of C atoms in 5.6 g of urea = (1 × 0.0933) mol × 6.022 × 1023 atoms/mol
= 0.562 × 1023 atoms of carbon
∴ Number of O atoms in 5.6 g of urea = (1 × 0.0933) mol × 6.022 × 1023 atoms/mol = 0.562 × 1023 atoms of oxygen.
∴ 5.6 g of urea contain 2.247 × 1023 atoms of H, 1.124 × 1023 atoms of N, 0.562 × 1023 atoms of C and 0.562 × 1023 atoms of O.