Two solutions are prepared. In Solution A, 5.0 g of a substance of molecular weight 50 is dissolved in 100 mL of pure water. In Solution B, 5.0 g of a substance with molecular weight of 75 is dissolved in 100 mL of pure water. The solute is non volatile and non ionic. Which solution will have the higher osmotic pressure?
They will be the same, because osmotic pressure depends only on the amount of solute.
Solution A
Solution B
They will be the same because the solvent is the same in both cases.
My answer: Solution A
Reason: solution A has a smaller molecular weight and therefore, a larger Molarity and higher osmotic pressure (pi=iMRT)
I agree.
Your reasoning is incorrect. The osmotic pressure of a solution does not solely depend on the molecular weight or molarity of the solute. It depends on the total number of particles present in the solution, which is determined by the concept of osmolality.
To calculate osmolality, you need to consider the total number of moles of solute particles present in the solution. This can be done by dividing the mass of the solute by its molecular weight:
Osmolality = (Mass of Solute / Molecular Weight of Solute) x 1000
For Solution A:
Osmolality of A = (5.0 g / 50 g/mol) x 1000 = 100 osmol/kg
For Solution B:
Osmolality of B = (5.0 g / 75 g/mol) x 1000 = 66.67 osmol/kg
Since the osmolality of Solution A is higher than Solution B, Solution A will have the higher osmotic pressure.
Therefore, the correct answer is Solution A.