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 )
