Asingle hydrogen atom has a mass of 1.67 × 10−24 g. a sodium atom has an atomic mass of 23. how many sodium atoms are required to reach a total mass of 973 mg in a substance of pure sodium?

                      2.55 × 10²² Na Atoms

Data Given:

                 M.Mass of Na  =   23 g.mol⁻¹

                 Mass of Na  =  973 mg  =  0.973 g

                 # of Na Atoms  =  ??

Step 1: Calculate Moles of Na as:

               Moles  =  Mass ÷ M.Mass

               Moles  =  0.973 g ÷ 23 g.mol⁻¹

               Moles  =  0.0423 mol

Step 2: Calculate No, of Na Atoms as:

As 1 mole of sodium atoms counts 6.022 × 10²³ and equals exactly to the mass of 23 g. So, we can write,

               Moles  =  No. of Na Atoms ÷ 6.022 × 10²³ Na Atoms.mol⁻¹

Solving for No. of Na Atoms,

               No. of Na Atoms  =   Moles × 6.022 × 10²³ Na Atoms.mol⁻¹

               No. of Na Atoms  =   0.0423 mol × 6.022 × 10²³ Na Atoms.mol⁻¹

               No. of Na Atoms  =  2.55 × 10²² Na Atoms

                          2.55 × 10²² sodium atoms are required to reach a total mass of 973 mg in a substance of pure sodium.