Question

How many water molecules are present in a drop of water at 4^oC(assume 20 drops per mL and density=1g/mL)

Answer 1

• The number of water molecules are present in a drop of water at 4^oC(assume 20 drops per mL and density=1g/mL) is:

$$\begin{gathered} Volumeof20drops=1mL \\ Therefore,volumeof1drop=\frac{1}{20}mL \\ Mass=volumexdensity \\ Mass=\frac{1}{20}x1=\frac{1}{20}=0.05grams \\ Molesofwater=\frac{1}{18}x0.05=\frac{0.05}{18}moles \\ Therefore,numberofmolecules=\frac{0.05}{18}x6.022x{10}^{23} \\ =1.67x{10}^{21}molecules \end{gathered}$$