Calculate the mass of 1 . 5 × 10 23 molecules of NH 3 .

Given, the number of molecules of NH 3 = 1 . 5 × 10 23 molecules We know that number of molecules = Number of moles × Avogadro's number Where the number of moles = Given mass Molar mass Molar mass of NH 3 = 1 × 14 + 3 × 1 = 17 gmol - 1 1 . 5 × 10 23 = Mass of NH 3 17 × 6 . 022 × 10 23 Mass of NH 3 = 1 . 5 × 10 23 × 17 6 . 022 × 10 23 = 4 . 23 g

Calculate the mass of 0 . 5 mole of CuSO 4 ⋅ 5 H 2 O .

Given, number of moles of CuSO 4 ⋅ 5 H 2 O = 0 . 5 moles Molar mass of CuSO 4 ⋅ 5 H 2 O = 1 × 63 . 5 + 1 × 32 + 4 × 16 + 5 × 18 = 249 . 5 gmol - 1 We know that, number of moles = Mass of CuSO 4 . 5 H 2 O Molar mass of CuSO 4 . 5 H 2 O 0 . 5 = Mass of CuSO 4 . 5 H 2 O 249 . 5 Mass of CuSO 4 . 5 H 2 O = 0 . 5 × 249 . 5 = 124 . 75 g