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How many moles would 6.022•1022 molecules of water represent?
Question Date: 2020-03-13
Answer 1:

One mole of a substance is defined as having exactly 6.02214076*1023 (*see note below) constitutive particles of that substance. Those particles can be atoms, ions, molecules, etc.

To determine the number of moles for some given number of molecules, one can use a simple but powerful technique known as dimensional analysis.

Dimensional analysis is essentially a method of converting units, involving multiplying given units by conversion factors and "canceling" like units that appear in both the numerator and denominator to reach the desired measure. Since this method works for any units, it is applicable for a wide range of problems. [Assuming the starting and ending units are of a consistent "type". For example, distances can only be measured in length units; trying to convert to 3 miles to pounds is nonsensical and impossible.]

For the present case, the given units are molecules of water and the desired units aremoles of water. The conversion factor is the definition of the mole, i.e., 1 mol H2O / 6.022...*1023 molecules H2O. Thus,
6.022*1022 molecules H2O * (1 mol H2O / 6.022...*1023 molecules H2O) ≈ 0.1 mol H2O.

*The mole used to be defined as the amount of a substance containing as many constitutive particles as the number of atoms of carbon-12 in 12 grams of carbon 12. The definition was changed in 2018/2019 to be
1 mole = 6.02214076*1023 (exact) particles. The US standards institute (NIST) has a fascinating (lengthy) article on this redefinition. Because the change is so recent, many articles/sites/textbooks will likely have the earlier definition still.

The responses to this question on ScienceLine and this chemistry page contain more information on using the mole/Avogadro's Number.

Answer 2:

Since 1 mole of particles is 6.022 x 1023, then the answer is:

Number of moles = (6.022 x 1022) / (6 x 1023) = 1 x 10-1 = 0.1 moles of water molecules.

Answer 3:

A mole of anything is 6.022•1023 particles. So, divide the number of molecules by Avogadro's number, and that's the number of moles.

Answer 4:

That's 0.1 mole of water, because 6 x 1023 is the number of molecules or atoms in a mole.

Answer 5:

Since one mole of anything (molecules, cars, bananas) is defined as 6.022*1023 of that thing, we can use this number to calculate how many moles of that thing we have. In this case, we can just divide 6.022*102 water molecules by 6.022*1023 molecules per mole. You should get an answer that is something like 10-x moles of water molecules.

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