Question

calculate the number of molecules in 1.5 mol of hydrogen chloride

Answer 1

M(HCl) = (1*1) + (35.5) = 36.5 g mol⁻¹

i.e., mass of 1 mol HCl is = 36.5 g

Number of moles in 1.5 g = 1.5/36.5 = 0.041 mol

1 mol HCl contains 6.0 * 10²³ molecules.

1.5 mol HCl contains 1.5 * 6.0 * 10²²

i.e. 1.5 mol HCl contains 15 * 6.0 * 10²²

⇒1.5 mol HCl contains 90 * 10²² molecules.