• Question: How much does a H2O particle weigh by its own?

    Asked by Default to Hummy, Lewis, James, Sandra on 10 Mar 2017.
    • Photo: Sandra Greive

      Sandra Greive answered on 10 Mar 2017:

      What are the molecular weights of the individual atoms? How many atoms and what type of atoms are in water? A: Two hydrogen and one oxygen atom. Molecular weight of hydrogen is basically 1 and the molecular weight of oxygen is almost 16. Therefore the molecular weight of water = 1 +1 + 16 = 18 grams/mole. That is 18 grams total for 6.022 x 10^23 molecules of water. At the beach on a warm day (25 degrees celsius) this would be equivalent to 1ml of water.

    • Photo: Lewis Wright

      Lewis Wright answered on 13 Mar 2017:

      As Sandra says, a mole is 6.022 x 10^23 molecules. How they arrived at it is very clever, and is the basis for a lot of chemistry since, so if you’re interested look up Avogadro’s number.

      The molar mass of water is 18.015 g/mol – as Sandra said, you get this from adding up the masses of two hydrogens and one oxygen.

      For the weight of one molecule, you divide the molar mass by Avogadro’s number:
      18.015 g/mol รท 6.022 x 1023 mol^-1 = 2.992 x 10^-23 grams

      There isn’t a lot of things to compare that to, so it’s hard to imagine!

      http://www.chemteam.info/Mole/Mass-One-Molecule.html

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