Question

What is the average volume occupied by 1 molecule of water (${{H}_{2}}O$)?
A. $3.99\times {{10}^{-23}}c{{m}^{3}}$
B. $2.99\times {{10}^{23}} cm^3$
C. $2.99\times {{10}^{-23}} cm^3$
D. $4.99\times {{10}^{-23}} cm^3$

Answer 1

Hint: We should be having an idea about the mole concept for solving this question. We should also be knowing the number of molecules that are present in one mole of water.

Step by step answer:
We know that the density of water is 1g/ml. This means 1 gram of water occupies a volume of 1 millilitre. We know that the atomic weight of hydrogen is 1 and that of Oxygen is 16. Therefore, the molecular mass of ${{\text{H}}_{\text{2}}}{\text{O}}$ is
$ = {\text{ }}2{\text{ }} \times {\text{ }}1{\text{ }} + {\text{ }}16{\text{ }} = {\text{ }}18$
Since, the molecular mass of ${{\text{H}}_{\text{2}}}{\text{O}}$ is 18, mass of 1 mole of water is 18g (according to the mole concept).
We know, 1 mole of a substance contains $6.022{\text{ }} \times {\text{ }}{10^{23}}$ molecules
Therefore, $6.022{\text{ }} \times {\text{ }}{10^{23}}$ molecules occupy 18g of water which in turn occupies a volume of 18ml.
Hence, 1 molecule of water will occupy
$\dfrac{{18}}{{6.022 \times {{10}^{23}}}}{\text{ }} \times {\text{ }}1{\text{ }} = {\text{ }}2.99{\text{ }} \times {\text{ }}{10^{ - 23}}{\text{ ml }} = {\text{ }}2.99{\text{ }} \times {\text{ }}{10^{ - 23}}{\text{ c}}{{\text{m}}^{ - 3}}$
Therefore, the correct answer is Option C.

Note: We should be knowing some unique properties of water that is a water molecule is slightly charged on both the ends because of the oxygen which is more electronegative as compared to the hydrogen.
Water has high heat of vaporization and also has cohesive and adhesive properties. Water is less dense as a solid than as a liquid.Water is also having high specific heat and it has the ability to expand when it's frozen. Liquid water has weak absorption bands at wavelengths of around 750 nm which cause it to appear to have a blue colour.