Adrop of water has a volume of approximately 7×10−2 ml. how many water molecules does it contain? the density of water is 1.0 g/cm3.

The number of molecules present in 7×10¯² mL of water is 2.34×10²¹ molecules  

Volume of water = 7×10¯² mL

Density of water = 1 g/mL

Mass = Density × Volume

Mass of water = 1 × 7×10¯²

From Avogadro's hypothesis,

1 mole of H₂O = 6.02×10²³ molecules

But

1 mole of water (H₂O) = (1×2) + 16 = 18 g

Thus,

18 g of H₂O = 6.02×10²³ molecules

Therefore,

0.07 g of H₂O = = 2.34×10²¹ molecules

Thus, 2.34×10²¹ molecules are present in 7×10¯² mL of water.

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The volume of drop of water is and density of water is .

Since,

Thus, volume will be  .

Mass of drop of water can be calculated from density and volume as follows:

To calculate number of water molecules first calculate the number of moles as follows:

Molar mass of water is 18 g/mol thus,

Now, in 1 mol of a substance there are molecules thus, number of molecules in 0.00388 mol will be:

Therefore, number of water molecules in drop will be .

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