Question

Calculate the number of molecules present in a drop of chloroform (CHCl₃) weighing 0.0239 g.
(Atomic mass : C = 12 u ; H = 1 u ; Cl = 35.5 u)

Answer 1

Mass of chloroform = 0.0239g
Molar mass of chloroform = (1 × 12) + (1 × 1) + (3 × 35.5) = 119.5g
Number of molecules in 119.5g of chloroform = 6.022 × 10²³
Number of molecules in 1g of chloroform = 6.022 × 10²³/119.5
Number of molecules in 0.0239g of chloroform = 0.0239 × 6.022 × 10²³/119.5
Hence, a drop of chloroform weighing 0.0239g has 1.2 × 10²⁰ molecules.