How many molecules approximately do you expect to be present in

(i) a small sugar crystal weighing 10 mg.

(ii) 1 drop of water with 0.05 cc volume.

(1). Sugar is chemically sucrose (C₁₂H₂₂O₁₁).

Molar mass of Sucrose = (12x12) + (22x1) + (11x16) = 342 g/mol

1 mole = 6.023 x 10²³ molecules of sucrose.

342 g = 6.023 x 10²³ molecules of sucrose.

10 mg (0.01 g) of sucrose = (6.023 x 10²³ x 0.01)/342 = 1.76 x 10¹⁹ molecules of sucrose.

(2). Density of water = 1 g/ml

Now, Density = Mass / Volume

So, (Volume of water in ml x 1) = Mass of water in gram

Volume of water in ml = Mass of water in gram

0.05 cc or 0.05 ml = 0.05 g 

Molar mass of water = 18 g/mol

18 g = 6.023 x 10²³ molecules of water.

0.05 g = (6.023 x 10²³ x 0.05)/18 = 1.67 x 10²¹ molecules of water.