Question

The density of the water at room temperature is 0.1g/ml. How many molecules are there in a drop of water if its volume is 0.05ml?

Answer 1

First we will calculate the mass of drop of water.

Mass = Density * Volume

Here, mass of drop of water = 0.1 * 0.05 = 0.005 g

Now , we will calculate moles of this drop

Number of moles = given molecular mass/molar mass

Moles = 0.005/18 = 0.00027 moles

Number of molecules = moles * avogadro number

Molecules = 0.00027 * 6.022 × 10^23

                 = 1.62 * 10^20

Answer = The number of molecules in a drop of water are 1.62 * 10^20