"To determine the amount of heroin in the mixture, you dissolve 1.00 g of the white powdery mixture in water in a 100.0-mL volumetric flask. You find that the solution has an osmotic pressure of 531 mm Hg at 25 °C. What is the composition of the mixture?"

Explanation:

Formula to calculate osmotic pressure is as follows.

 Osmotic pressure = concentration × gas constant × temperature( in K)

Temperature =

                      = (25 + 273) K

                      = 298.15 K  

Osmotic pressure = 531 mm Hg or 0.698 atm     (as 1 mm Hg = 0.00131)

Putting the given values into the above formula as follows.

       0.698 =

               C = 0.0285

This also means that,

  = 0.0285

So,     moles = 0.0285 × volume (in L)

                      = 0.0285 × 0.100

                     =

Now, let us assume that mass of = x grams

And, mass of = (1.00 - x)

So, moles of

                              =

Now, moles of

                   =

                  =

             = x = 0.346

Therefore, we can conclude that amount of present is 0.346 g  and amount of present is (1 - 0.346) g = 0.654 g.