Question

Calculate the number of molecules in a drop of water. Given that 20 drops of water weigh 1.2 g. ​

Answer 1

Mass of 20 drops of water = 1.2g

Mass of 1 drop of water = 1.2/20 = 0.06g

Molar mass of water = 18g

Moles of water = given mass / molar mass

= 0.06/18

= 0.0033

Therefore, no. Of water molecules,

= 0.0033 X 6.022 X 10^23

= 0.0198 X 10^23

= 1.98 X 10^23

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Answer 2

Answer:

1ml of water weighs 1 gram. Dividing that by 20 you will get 0.05 grams of water moleciules. The molecular mass of one water molecule (in terms of moles) is about 18.02. If we divide the mass of the water by water its molecular mass, we can find the number of moles:

0.05/18.02= 0.00028

One mole is equal to 6.022*10^23

Multiplying these to values together we get the final answer of 1.69*10^20 molecules of water. Thats an absurd let huge number which is why we prefer to work in moles.

Molecular mass can be found by adding the atomic masses (found in the periodic table usually in the bottom left of the elementary although some outliers mean that it usually worth just using the bigger number written) of all the components. For water or dihydrogen monoxide, there are 2 hydrogens and 1 oxygen; hydrogen has an atomic mass of 1.01 while oxygen has an atomic mass of 16.00.

1.01*2 + 16.00 = 18.02

Alternatively you can goo.gle it :P

I also think it's worth saying that a lot of these numbers are rounded so if you were to use the full numbers the number could be a tiny bit bigger or smaller but not enough to matter for the most part.

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