Question

The mass of molecule of water is:

Answer 1

Identify the atoms present in a molecule of water. After that identify the mass of each atom present in water. The total sum of mass of an individual atom will give the mass of 1 molecule of water.

Complete step by step answer:
Water is a polar inorganic compound that is tasteless, odourless and almost colourless at room temperature. Water is considered as the universal solvent as many solutes readily dissolve in water. It is the most abundant substance of earth.
Water exists in a liquid state of matter at 298 K which is considered as room temperature.
We will now identify the atoms present in one molecule of water. As suggested in the hint we will write down the mass of each atom and then find the total sum. This total sum will be the molecular mass of water.
The elements present are oxygen and hydrogen.
Mass of oxygen atom = 16 g
Mass of hydrogen atom = 1 g
Since 1 oxygen atom combines with 2 atoms of hydrogen,
The total mass of water becomes,
Mass = (2 x 1) + (1 x 16) = 18 g
Therefore, the mass of a molecule of water is 18 g.

Note: Water exists as a liquid because there is strong hydrogen bonding between the water molecules due to high electronegativity of oxygen atom.
However, the extent of hydrogen bonding starts reducing as we move down the group. In fact, the very next hydride, hydrogen sulphide exists as a gas. This is because the electronegativity is lesser than oxygen and thus the hydrogen bond formed is very weak.