# 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?

sanjeetmanna | College Teacher | (Level 3) Assistant Educator

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Density = mass/volume.

Mass = Density * Volume.

Given

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 | Elementary School Teacher | eNotes Newbie

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mromezy12,

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).

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

Posted on

d=m/v

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 | 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

now

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 | High School Teacher | (Level 3) Valedictorian

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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.