How many molecules are in 20 grams of NH3?

Question

How do I get moles and molecules of NH3?

Answer 1

Dimensional analysis: (20g NH₃) * (1 mole NH₃ / 17.0g NH₃) = 1.1₈ ≅ 1.2 mole NH₃ (2 sig figs).

(1.18 mole) * (6.022 x 10²³ molecules/ 1 mole) = 7.1 x 10²³ molecules.