Which of the following solutions will have maximum osmotic pressure? Assume 90% dissociation of each salt:
(a) Decimolar aluminium sulphate
(b) Decimolar barium chloride solution
(c) Decimolar sodium sulphate solution
(d) Solution of equal volumes of decimolar barium chloride and decimolar sodium sulphate solutions
Answer (2)
The solution of equal volumes of decimolar barium chloride and decimolar sodium sulfate will have the maximum osmotic pressure with an effective concentration of 0.6 M. The aluminium sulfate solution follows at 0.5 M, while barium chloride and sodium sulfate are at 0.3 M each. Therefore, option (d) is correct.
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To determine which of the given solutions has the maximum osmotic pressure, we need to use the formula for osmotic pressure, which is given by:
Π = i CRT
Where:
Π is the osmotic pressure.
i is the van 't Hoff factor, which accounts for the number of particles the solute dissociates into.
C is the molarity of the solution.
R is the ideal gas constant.
T is the temperature in Kelvin.
Since all solutions are decimolar and presumably at the same temperature, the key factor affecting osmotic pressure will be the van 't Hoff factor i .
Let's calculate the i for each solution, considering 90% dissociation:
Decimolar Aluminium Sulphate ( A l 2 ( S O 4 ) 3 ) :
It dissociates into 2 Al 3 + ions and 3 SO 4 2 − ions, giving 5 ions per formula unit.
With 90% dissociation, i = 1 + 0.9 × 4 = 4.6 .
Decimolar Barium Chloride ( B a C l 2 ) :
It dissociates into 1 Ba 2 + ion and 2 Cl − ions, giving 3 ions per formula unit.
With 90% dissociation, i = 1 + 0.9 × 2 = 2.8 .
Decimolar Sodium Sulphate ( N a 2 S O 4 ) :
It dissociates into 2 Na + ions and 1 SO 4 2 − ion, giving 3 ions per formula unit.
With 90% dissociation, i = 1 + 0.9 × 2 = 2.8 .
Solution of equal volumes of Decimolar Barium Chloride and Decimolar Sodium Sulphate solutions:
Mixing these solutions will form a complex mixture including BaSO 4 which may precipitate, leaving Na + and Cl − ions in solution.
Due to precipitation and other complex effects, evaluating i is not straightforward here.
Comparing the i values:
Aluminium sulphate has the highest i value at 4.6.
Therefore, the solution with decimolar aluminium sulphate will have the maximum osmotic pressure.
So, the chosen option is (a) Decimolar aluminium sulphate .
