question_answer

2.56 g of sulphur present in 100 mL of solution in colloidal form shows an osmotic pressure of 2.463 atm at 300 K. How many atoms of sulphur get associated to form the colloidal sol?

Answer:

                Let us calculate the observed molar mass of sulphur in the colloidal solution with the help of Van't Hoff equation: \[\pi =\,\frac{{{W}_{B}}RT}{{{M}_{B}}V}\,\,\,\,or\,\,\,\,{{M}_{B}}\,=\frac{{{W}_{B}}RT}{\pi V}\] \[{{M}_{B}}=\frac{\text{(2}\text{.56g) }\!\!\times\!\!\text{ (0}\text{.821}\ \text{L}\,\text{atm}\,{{\text{K}}^{\text{-1}}}\,\text{mo}{{\text{l}}^{\text{-1}}}\text{) }\!\!\times\!\!\text{ (300K)}}{\text{(2}\text{.463}\,\text{atm)}\,\text{ }\!\!\times\!\!\text{ (0}\text{.1}\,\text{L)}}=256\,\,\text{g}\,\text{mo}{{\text{l}}^{\text{-1}}}\] Gram atomic mass of sulphur \[=32\,g\,mo{{l}^{-1}}\] \[\therefore \] No. of sulphur atoms associated \[=\frac{(256\,g\,mo{{l}^{-1}})}{(32\,g\,mo{{l}^{-1}})}=8\].