Question

Define the molecular mass of the substance.

Answer 1

Part 1: Molecular mass of a substance:

• The molecular mass of a substance is the sum of the atomic masses of all the atoms present in a molecule of that substance.
• The molecular mass of a compound is defined as the mass of one molecule.

Part 2: Unit of molecular mass:

• The unit of molecular mass is atomic mass unit $\left(\mathrm{amu}\right)$ or simply $\mathrm{u}.$
• The molecular mass of water $\left({\mathrm{H}}_2\mathrm{O}\right)$$=2\times \mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{H}+1\times \mathrm{atomic}\mathrm{mass}\mathrm{of}\mathrm{O}$

$=2\times 1+1\times 16=2+16=18\mathrm{amu}\mathrm{or}\mathrm{u}$.