Question

Determine the molecular mass of water.

Answer 1

Hint : Molecular mass is the total mass of the given molecule. We should know the atomic mass of every element that is present in the molecule and by adding the atomic mass of all the elements we can get the molecular mass of the molecule.

Complete Step-by-Step answer:
-The molecule of water consists of two molecules of hydrogen and one molecule of oxygen.
-From the periodic table, we know that the atomic mass of the hydrogen is 1 g/mol and oxygen has the atomic mass 16 g/mol.
-We know that a total of two molecules of hydrogen makes the bond with the oxygen, so the molecular mass of water will be:
- (No. of molecules of hydrogen × mass of hydrogen) + atomic mass of oxygen
$\begin{aligned} & \left( 2\text{ }\cdot \text{ 1} \right)\text{ + 16} \\\ & \text{2 + 16 = 18} \\\ \end{aligned}$
-Therefore, the molecular mass of water is 18 g/mol.
Additional Information: Water is a polar molecule which is colourless, tasteless as well as odourless.
-Water can be in three states of matter i.e. solid, liquid and gas at $\text{0}{}^\circ \text{C, 37}{}^\circ \text{C and 100}{}^\circ \text{C}$.
-Due to the presence of hydrogen bonding in the water molecules, it has high surface tension.
-Water has a density of 1 gm per cubic centimetre.

Note : To calculate the correct molecular mass it is necessary to have a correct molecular formula. In water, hydrogen bonding is present. Oxygen consists of a negative charge whereas hydrogen consists of a positive so bond formation takes place between the neighbouring oxygen and hydrogen. SI unit of molecular mass is g/mol.