​Calculate the no. of mililiters of stp of H2S gas needed to percipitate cupric sulphide completely from 100 ml of a solution containing 0.75g of CuCl in 1l.
CuCl2 + H2S ---- CuS + 2HCl

Dear Student

The reaction involved is:

CuCl₂ + H₂S ----> CuS + 2HCl

​Mass of solution = 100 mL

​Mass of CuCl = 0.75 g or 0.75 mL (because 1 gm = 1 mL)

​Mass of H₂S = (100 - 0.75) mL = 99.25 mL

​Therefore, No. of moles = $\frac{Mass}{Molar Mass}$
So, No. of moles of ​CuCl₂ = $\frac{ 0.75 g}{134.45 g/mol}$ = 0.0055 mol

No. of moles of H₂S = $\frac{99.25}{34.08}$ = 2.912 mol

​Molarity = $\frac{No. of moles}{Volume of solution in L}$

             = $\frac{2.912 mol}{0.1 L}$ = 29.12 mol/L