Question

Given that each of the following aqueous solutions is at the same temperature, which has the largest osmotic pressure? (Assume ideal behavior).

A. 0.0030 M lithium phosphate, Li3PO4

B. 0.0060 M magnesium chloride, MgCl2

C. 0.0020 M aluminum sulfate, Al2(SO4)3

D. 0.0070 M ammonium nitrate, NH3NO3

E. 0.014 M CH3OH, (methanol)

Please provide an explanation.

Answer 1

osmotic pressure,
P = i*C*R*T
T is same for all and R is constant
C is concentration here
So, P will be maximum when i*C is maximum

A)
i=4 as Li3PO4 dissociates into 3 Li+ and 1 PO43-
i*C = 4*0.0030 = 0.0120

B)
i = 3 as it dissociates into 1 Mg2+ and 2 Cl-
i*C = 3*0.0060 = 0.0180

C)
i = 5 as it dissociates into 2 Al3+ and 3 SO42-
i*C = 5*0.0020 = 0.010

D)
i=2 as it dissociates into 2 NH4+ and 3 NO3-
i*C = 2*0.0070 = 0.0140

E)
i=1 as CH3OH is non electrolyte
i*C = 1*0.014 = 0.014 M

Answer: B