Question

Calculate the number of molecules in 0.020 mg Fe

Answer 1

Molar mass of iron, M = 55.855 g/mol

0.020 mg of iron

= 0.020 × 10^-3 g

= [0.020 × 10^-3 g / 55.855 (g/mol)]

= 3.58 × 10^-7 mol

In 1 mol of any substance number of molicule = 6.023×10²³ mol^-1

In 3.58 × 10-7 mol of substance number of molicule = 3.58 × 10^-7 mol × 6.023×10²³ mol^-1

= 2.156 × 10¹⁷

Hence in 0.020 mg of Fe number of molicule = 2.156 × 10¹⁷