# 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

Jul 10, 2018

$0.432$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

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

#### Explanation:

By definition, there are $6.022 \times {10}^{23}$ 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 $2 \times {N}_{A}$ hydrogen atoms...and the mass associated with this numerical quantity of water molecules is approx. $18 \cdot g$...

And so we simply take the quotient....

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

$= 0.432 \cdot m o l$...and thus a mass of $0.432 \cdot m o l \times 18.01 \cdot g \cdot m o {l}^{-} 1 = 7.78 \cdot g$...

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 $1 \cdot g$ more or less precisely.. which is why we use this absurdly large quantity .. Capisce?