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Question:

Consider separate solutions of 0.500 M C2H5OH(aq), 0.250 M KBr(aq), 0.125 M Na3PO4(aq), and 0.1 M Mg3(PO4)2 at 25°C. Which statement is true about these solutions, assuming all salts to be strong electrolytes?

They all have the same osmotic pressure.

0.125 M Na3PO4(aq) has the highest osmotic pressure.

0.500 M C2H5OH(aq) has the highest osmotic pressure.

0.100 M Mg3(PO4)2(aq) has the highest osmotic pressure

Solution:

For C2H5OH, π = 1 × 0.5 × RT
For KBr, π = 2 × 0.25 × RT
For Mg3(PO4)2, π = 5 × 0.1 × RT
For Na3PO4, π = 4 × 0.125 × RT
So, all are isotonic solutions.