How many moles of #"H"_2"O"# contain #2.60 * 10^23# molecules of water?

The answer is 0.432 mole of H2O but I dont know how to get that answer. I dont know how to set up the problem

2 Answers
Jul 10, 2018

Answer:

#0.432#mol

Explanation:

Divide the given number of molecules by Avogadro's constant. Avogradro's constant is the number of atoms/molecules in a mole of a substance.

Therefore,

#(2.60 * 10^23 \ "molecules")/(6.022 * 10^23 \ "molecules/mol") = "0.432175 moles" ~~ "0.432 moles"#

Jul 10, 2018

Answer:

Well, how molecules are present in ONE MOLE of water...?

Explanation:

By definition, there are #6.022xx10^23# such molecules, or #N_A# such molecules in ONE mole of water. And thus in such a quantity there are #N_A# oxygen atoms, and #2xxN_A# hydrogen atoms...and the mass associated with this numerical quantity of water molecules is approx. #18*g#...

And so we simply take the quotient....

#"Moles of water"=(2.60xx10^23*"water molecules")/(6.022xx10^23*"water molecules"*mol^-1)#

#=0.432*mol#...and thus a mass of #0.432*molxx18.01*g*mol^-1=7.78*g#...

Instead of the mole, we could use the dozen, or the gross, or some other numerical quantity ... it just happens that one mole of hydrogen ATOMS have a mass of #1*g# more or less precisely.. which is why we use this absurdly large quantity .. Capisce?