Anonymous asked in Science & MathematicsChemistry · 1 decade ago

Mass of One Water Molecule?

The answer says the mass of one water molecule is

2.99 X 10^-23 g.

I do not know how to get that answer. I thought that the mass of one water molecule would be the molecular mass of H2O, which is 18 amu.

Clearification is much appreciated. Thanks in advance =]

6 Answers

  • 1 decade ago
    Favorite Answer

    Alright i've gotten a couple thumbs down on this one and i'm not quite sure why, so i'll add a narrative:

    they are both correct. 1 amu = 1 g/mol .....amu and g/mol are interchangable.

    and we know there are 6.022 * 10^23 molecules in 1 mole.

    1 mol = 6.022 x 10^23 molecule

    So to change our units from g/mol to grams per molecule, we multiply g/mol by mol/molecule, there is a mol on top and bottom, and they cancel out, and leave you with the answer in grams/molecule

    18.0 g/mol * (1 mol) / (6.022 * 10^23 molecules) = 2.99 * 10^-23 g/molecule

    • Login to reply the answers
  • lents
    Lv 4
    3 years ago

    Molecular Mass Of Water

    • Login to reply the answers
  • n b
    Lv 5
    1 decade ago

    What is the mass of one molecule of H2O?

    Step #1 - the molar mass of water is 18.015 g/mol. This was calculated by multiplying the atomic weight of hydrogen (1.008) by two and adding the result to the weight for one oxygen (15.999).

    Please remember that you need the molar mass first when trying to find the mass of one molecule.

    Step #2 - divide the substance's molar mass by Avogadro's Number.

    18.015 grams/mol ÷ 6.022 x 1023 mol¯1 = 2.992 x 10¯23 grams

    Note that the final answer has been rounded to four significant figures (from 2.9915 - note use of rounding with five rule) and that the unit of mole cancels.

    • Login to reply the answers
  • pontow
    Lv 4
    3 years ago

    Molecular Weight Of Water

    • Login to reply the answers
  • How do you think about the answers? You can sign in to vote the answer.
  • 4 years ago

    For the best answers, search on this site

    molecular weight of water=18 so the mass of a water molecule=18* mass of hydrogen atom=18*atomic mass unit.

    • Login to reply the answers
  • Anonymous
    4 years ago

    It takes 10 seconds for YAnswers web page to load for me to be able to click on [add your answer] box. does this mean my laptop is slow?

    • Login to reply the answers
Still have questions? Get your answers by asking now.