Calculate the number of molecules of sulphur (S 8 ) present in 16 g of solid sulphur.

 

Answer

We know that,

Number of moles of a substance = Given mass of the substance / Molar mass of the substance

                                                                n  = m/M ----- (1)

Also,

Number of moles of a substance = Number of particles of the substance / Avogadro's Constant

 n  = N / N O

n  = N / 6.022 x 10 23 ------- (2)

From the above 2 formulae, we can say that,

 n = m / M = N / 6.022 x 10 23   ---- (3)



Given mass of sulphur molecule(S 8 ) = m = 16g

Molar mass of Sulphur Molecule (S 8 ) = M = 256g

 

We need to find Number of molecules, ie, N

 

Putting values in (3), we get

16 / 256 = N / 6.022 x 10 23  

N = 6.022 x 10 23   x (16 / 256)

   = 6.022 x 10 23   / 16

   = 3.011 x 10 23 /8

   = 0.37 x 10 23 molecules of Sulphur(S 8 )

   = 3.7 x 10 22 molecules of Sulphur (S 8 )

  1. Class 9
  2. Chapter 3 Class 9 - Atoms And Molecules (Term 2)

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo