Question

Calculate no. of molecules in 1 drop of water having mass .05g

Answer 1

Molecular mass of water = 18 g

No. of moles in 0.05 g of water = 0.05/18

   = 2.78 x 10-3 mol

One mole = 6.023 x 1023 molecules

Therefore, 2.78 x 10-3 mol of water contain = 2.78 x 10-3 6.023 x 1023 molecules

  = 1.67 x 1021 molecules

Answer 2

First find no. of moles in 1 drop

So Molar mass = 18

n = m / M

= 0.05 / 18

= 0.002 moles

Now

1 mole contains 6.022 × 10^23 molecules

0.002 contains 0.002 × 6.022 × 10^23

1.20 × 10^21 molecules



Thanks