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

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mgomezy12 | Student, College Freshman | eNotes Newbie

Posted February 6, 2009 at 2:37 AM via web

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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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kmieciakp | High School Teacher | Valedictorian

Posted February 7, 2009 at 10:38 AM (Answer #1)

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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.)

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sarahyama | Elementary School Teacher | eNotes Newbie

Posted May 20, 2009 at 2:59 PM (Answer #2)

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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).

the answer would be 8.56x10^22

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sanjeetmanna | College Teacher | (Level 3) Assistant Educator

Posted July 1, 2012 at 10:01 PM (Answer #3)

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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.

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chaobas | College Teacher | Valedictorian

Posted July 3, 2012 at 3:39 AM (Answer #4)

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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

 

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neela | High School Teacher | Valedictorian

Posted June 8, 2009 at 2:34 PM (Answer #5)

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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.

 

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