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I thought that molar mass is the mass of one mole of a substance whereas molecular mass is the mass of one molecule of a substance.
But the molecular mass of water is 18.2 u, which is similar to its molar mass i.e. 18.02 g/mol.
Are these two different and how?
Molecular mass is the mass of a single molecule
Molar mass refers to the mass of 1 mole of molecules, ie $ 6.023 × 10^{23}$ of them.
Eg: Molecular mass of $\ce{H2}$ is about $3.32 \times 10 ^{-24}\ \mathrm g$ or about $2\ \mathrm u$.
Here "$\mathrm u$" is just a unit,
$1\ \mathrm u = 1.66 \times 10^{-24}\ \mathrm g$
Whereas molar mass is about $2\ \mathrm{g/mol}$.
