Question

If 10²¹ molecules are removed from 200 mg of H₂S. Calculate the number of moles present in H₂S. 

Answer 1

Molecular weight of H₂S = 2 + 32 = 34 g

Number of molecules in 34 g H₂S = 6.022 × 10²³ 

Number of molecules in 200 × 10^-3 g H₂S 

\( = \frac{6.022\times10^{23}\times200\times 10^{-3}}{34}\)

= 35.41 × 10²⁰ 

= 3.54 × 10²¹ molecules. 

Number of molecules removed = 10²¹ 

So, no. of remaining molecules 

molecules 

= 3.54 × 10²¹ - 1.00 × 10²¹ 

= 2.54 × 10²¹ molecules. 

∵ 6.022 × 10²³ H₂S molecules are present = 1 mol H₂S 

∵ For 2.54 × 10²¹ H₂S molecules = imm mol H₂S 

= 4.2 × 10^-3 mol H₂S