Question

How many molecules of water are present in a drop of water which has a mass of 50mg?

Answer 1

now, we know that

the molar mass of water = 18 gms/mol

and

the number of molecular in a molar mass of any substance would be = 6.023 x 10²³ molecules

so,

1 gram of water will have = (6.023 x 10²³) / 18

so,

the number of molecules in one drop (50mg = 0.05 gm) of water = [(6.023 x 10²³) x 0.05] / 18

thus, we get

number of molecules = 1.673 x 10²¹ molecules