Question

The mass of one mole of water is approximately is:
A. $\dfrac{18}{6.023\times {{10}^{23}}}$
B. $\dfrac{36}{6.023\times {{10}^{23}}}$
C. $\dfrac{6.023\times {{10}^{23}}}{18}$
D. $\dfrac{18}{6.023\times {{10}^{22}}}$

Answer 1

Hint: We should be knowing the proper formula to find out the mass of one mole of water. Even the molecular mass of water should also be known.

Step by step answer:
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
Hence, 1 molecule of water will occupy
     \[\dfrac{18}{6.022\times {{10}^{23}}}\text{ }\times \text{ }1\text{ }=\text{ }2.98\text{ }\times \text{ }{{10}^{-23}}\text{ }g\]
Therefore, the mass of one molecule of water is equal to
$\dfrac{18}{6.023\times {{10}^{23}}}$.
Hence, the correct answer is Option A.

Note: We should be knowing that mole in chemistry is a standard scientific unit for measuring large quantities of very small entities such as atoms, molecules or other specified particles.
It was a bridge between atoms and the macroscopic amounts of material that we work with in the laboratory. It allows the chemist to without an amount of two substances such as iron and sulphur in a way such that equal numbers of atoms of iron and sulphur are obtained.
About water we should know that a water molecule is slightly charged on both ends. This happens because of the oxygen which is more electronegative than the hydrogen, which forms the water molecule.