The density of water is 1.00g/mL at 4'C. How many water molecules are present in 2.56mL of water at this temperature?

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sanjeetmanna's profile pic

sanjeetmanna | College Teacher | (Level 3) Assistant Educator

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Density = mass/volume.

Mass = Density * Volume.


density = 1g/ml

Volume = 2.56 ml

Mass = 1 * 2.56 = 2.56 g.

We know 1 mole contain 6.02 x 10^23 molecules.

Moles = mass/molar mass

         = 2.56/18    [ Molar mass of water = 18]

         = 0.142.

Therefore 0.142 moles of water will contain 0.142 * 6.02 x 10^23 molecules = 8.5484 * 10^22 molecules.

So 2.56 ml of water at that temperature contain 8.5484 * 10^22 molecules.

sarahyama's profile pic

sarahyama | Elementary School Teacher | eNotes Newbie

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To get the molecules, you should first solve how many grams of water are present. So you should multiply the density with the volume.

1.00g/ml times 2.56 ml is equal to 2.56g of water.

then multiply the mass with the molar mass of water. in water there are two hidrogen molecules and 1 oxygen molecule, so the molar mass would be 18.

Deviding 2.56g by 18g would give mole number of the water and to get the number of the molecules, you should times avogdro's number(6.23x10^23).

the answer would be 8.56x10^22

kmieciakp's profile pic

kmieciakp | High School Teacher | (Level 2) Assistant Educator

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solve for m.

deterimine moles by dividing m by molecular weight (be sure to use same units).

determine molecules by mulitplying resulting moles by mole number (it's been awhile--I think it's 6.24 x 10 to the 23? called Avegerros' number? anyway, you can look it up.)

chaobas's profile pic

chaobas | College Teacher | (Level 1) Valedictorian

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Here the density of water is 1g/ml and the volume is given as 2.56 mL



density = mass/volume

mass = densitys * volume

Mass of water = (1.00 g/mL ) * (2.56 mL) = 2.56 gram


now the molar mass of water is 18 g/mol.

mole = mass/molar mass

Moles of water = (2.56 g)/(18 g/mol) = 0.142 mol of water


 we know that 1 mole of any substance has s6.023*10^23 molecule

so 0.142 mol of water will have

0.142 mol water * (6.023*10^23 molecule of water/ 1 mol of water)

8.55*10^22 molecule of water


neela's profile pic

neela | High School Teacher | (Level 3) Valedictorian

Posted on

18 gram of water contains 1 mole of water molecules.

The density of water at 4 deg C =1.00gm/mL.

Therefore, water by mass in 2.56 mL = =volume*density=2.56*1=2.56gm.

Number of water molecules in 1 gm of water=(1/18)mole=(6.022137 × 10^23 )/18molecules

Therefore  the number of water molecules 2.56 gm of water:

=(2.56)(6.022137 × 1023)/18=8.564817067*10^22molecules of water.


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