Question

what is the mass of the water molecule in gm ?How many molecules are prezent in one droup of pure water which weighs 0.05gm . If the same water drops evaporate in 1 hr calculate the number of molecules leaving the liquid surface per second​

Answer 1

Hi Friend

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The average mass of one H2O molecule is 18 amu. The number of atoms is an exact number, the number of mole is an exact number; they do not affect the number of significant figures. The average mass of one mole of H2O is 18.02 grams. This is stated: the molar mass of water is 18 g/mol.

1 Mole = 18 grams = 6.022 x 10^23 molecules

1 gram = 6.022 x 10^23/18 molecules

5/100 grams = 6.022   x 10 ^23 /18 X 5/100 molecules

                    = 6.022 x 10 ^21/18 X 5

                    = 30.11 x 10 ^ 21 /18

                    =1.67 x 1^21 molecules.

hope it's help you :)