Question

Which of the following has the lowest osmotic pressure at 25 C? Assume that the ionic compounds dissociate completely.

a) 0.10 M aqueous sodium chloride

b) 0.10 M aqueous calcium chloride

c) 0.10 M aqueous aluminum chloride

d) 0.10 M aqueous glucose

Answer 1

   = iMRT

a) 0.10 M aqueous sodium chloride

     NaCl (aq) -------------> Na^+ (aq) + Cl^- (aq)

               i = 2

              T = 25⁰C    = 25 + 273 = 298K

           = iMRT

               = 2*0.1*0.0821*298    = 4.893atm

b) 0.10 M aqueous calcium chloride

         CaCl2 (aq) ------------------> Ca^2+ (aq) + 2Cl^- (aq)

                            i = 3

         = iMRT

               = 3*0.1*0.0821*298    = 7.34atm

c) 0.10 M aqueous aluminum chloride

       AlCl3(aq) ----------------> Al^3+ (aq) + 3Cl^- (aq)

                   i = 4

      = iMRT

               = 4*0.1*0.0821*298    = 9.79atm highest osmotic pressure

d) 0.10 M aqueous glucose

glucose is non ionisable

      i= 1

   = iMRT
               = 1*0.1*0.0821*298    = 2.45atm >>>>>lowest osmotic pressure >>>>>answer