Question

The volume of a drop of water is 0.04 ml. How many H₂O molecules are there in a drop of water. Density of water = 1.0 g/ml.

Answer 1

Mass of 1 drop of water = Volume x density

= 0.04 ml x 1.0 g/mol = 0.04 g

Molecular mass of H₂O = 2 x 1 + 16 = 18 μ

One mole of H₂O weighs 18 g and contains 6.023 x 10²³ H₂O molecules.

Number of H₂O molecules in 0.04 g H₂O

= {6.023 x 10²³ molecules}/{18 g} x 0.04 g

= 1.3384 x 10²³ molecules