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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?

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  • $\begingroup$ 33 kilograms of something and 33 grams of it look pretty similar in writing. They feel different, though. $\endgroup$ Commented Jun 11, 2019 at 11:11
  • $\begingroup$ The molecular mass is the mass of one molecule in amu (atomic mass units). $\endgroup$ Commented Jun 11, 2019 at 13:28
  • $\begingroup$ That is like saying my car can go 92 mph, and the distance from home to the big city is 92 miles, so those two are similar. However, one is a speed and the other a distance. (And the reason they are similar is because in my world, an hour is defined as the time it takes my car to go to the big city at maximal speed). $\endgroup$
    – Karsten
    Commented Jun 11, 2019 at 15:11

1 Answer 1

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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 $2\ \mathrm{g/mol}$.

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