What is the approximate mass of one water molecule?

Question

Luna Chen · Accepted Answer

You can determine that by using the molar mass in #"g/mol"# of the water molecule and converting so that you get the absolute mass in #"g"#. The molar mass is #"MM"_("H"_2"O")" = 18.015 g/mol"#.  In the event that you are unable to recall, you can also check Wikipedia for information on it or use a periodic table to calculate the molar masses of two hydrogen atoms and one oxygen atom. #"MM"_("H"_2"O") = 2*"1.0079 g/mol H" + "15.999 g/mol O"# #= "18.015 g/mol H"_2"O"# Now we just need the relationship between the units #"mol"# and #"number of things in a mol"#. You may have been taught Avogadro's number, which is #6.0221413xx10^(23) "things/mol"#, and you can use that for the stoichiometric conversion. You multiply by the reciprocal to cancel out the units because the goal for the final units is #"absolute mass"/("molecule H"_2"O")#. #("18.015 g H"_2"O")/cancel("mol H"_2"O") xx cancel("1 mol H"_2"O")/(6.0221413xx10^(23) "molecules of H"_2"O")# #= color(blue)(2.9915xx10^(-23) "g/molecule H"_2"O")#

Natalie Anton · Answer

undefined A single water molecule has an approximate mass of 18.015 daltons, or atomic mass units (amu).