Question

A drop of water is about 0.05 mL. The density of, water at room temperature is about $ 1.0\,\text{m}{{\text{L}}^{-1}}. $ The number of water molecules present in a drop of water are.

• A. $ 1.67\times {{10}^{21}}{{H}_{2}}O $ molecules
• B. $ 1.67\times {{10}^{26}}{{H}_{2}}O $ molecules
• C. $ 1.806\times {{10}^{23}}{{H}_{2}}O $ molecules
• D. $ 1.806\times {{10}^{21}}{{H}_{2}}O $ molecules

Answer 1

Answer: (A)

$ d=\frac{m}{v} $ or mass of 0.05 mL water
$ =0.05\,mL\times 1.0\,g\,m{{L}^{-1}} $
$ =0.05\,g\,{{H}_{2}}O $
Moles of $ {{H}_{2}}O=\frac{0.05}{18}mol\,{{H}_{2}}O $
$ =\frac{6.023\times {{10}^{23}}\times 0.05}{18} $
$ =1.67\times {{10}^{21}}\,{{H}_{2}}O\,\text{molecules} $