General Knowledge - Chemistry - Discussion

Here One drop of water has the volume 0.0018 mL.
Because the density of water is 1, the mass is 0.0018 g. The molar mass of water (H2O) is 18.0 grams/mol (1.008 + 1.008 + 16.0). This means there is one mole of water in 18.0 grams. One mole is 6.02 x 1023 molecules.

Then you can convert grams to number of atoms:
0.0018 grams / 18.0 grams x (6.02 x 10exp19 molecules)

Read more: http://wiki.answers.com/Q/How_many_water_molecules_are_in_one_drop_of_water#ixzz1iphXiIJy

First using the density formula, convert volume to mass then divide the mass substance from molecular weight of compound.

You will get the answer for any molecules.

Why should taken (6.02 x 10exp19 molecules) molecule, if Avogadro.No is 6.023 x 1023?

Can you explain?

In the question the volume of water is given. To relate this we must have to used volume of one mole equals to 22.4 lit rather than gram molecular mass.

Number of mole = Molecule.wt*Avogadros no. Thus by multiplying both we get answer.

Density of water = 1.

So 1 = mass/volume, 1 = mass/0.0018, mass = 0.0018g no. of mole = weight/molecular

weight = 0.0018/18.

No of water molecules = No of mole*Avogadros no.

= 0.0018/18*6.023*10exp23 = 6.023*10exp19.

Here, d = m/v equal to 0.0018 g so we can write as 18 * 10^-4 g.
Then n = 18 *10^-4/18 = 1 * 10^-4.
One mole = 6.022 * 10^23.
1 * 10^-4 mole = x
And the answer is 6.022 * 10^19.

Here, we must have to deal with volume rather than density then the answer will be different. We have to take the volume of one mole of water (22400ml).

How do you get 18 out of .0018?

Please clear my doubt.

1mol of H2O contains 6.023*10^23 molecules.

Here, mol=volume/atomic weight=0.0018/18 (h2o at weight =18) = 0.0001.
0.0001 mol H2O contains 6.023*10^23*0.0001 = 6.023 * 10^19 molecules.