Question
Consider separate solution of 0.500 M C2H5OH (aq), 0.100 M Mg3(PO4)2 (aq) 0.250 M KBr (aq) and 0.125 M Na3PO4 (aq) at 25oC. Which statement is true about these solutions, assuming all salts to be strong electrolytes?
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They all have the same osmotic pressure
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0.100 M Mg3(PO4)2 (aq) has the highest osmotic pressure
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0.125 M Na3PO (aq) has the highest osmotic pressure
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0.500 M C2H5OH (aq) has the higest osmotic pressure
Solution
A.
They all have the same osmotic pressure
effective molarity = Van't Hoff factor x molarity
0.5 M C2H5OH (aq) i =1
Effective molarity = 0.5
0.25 M KBr (aq) i = 2
Effective molarity = 0.5
0.1 M Mg3(PO4)2 (aq) i = 5
Effective molarity = 0.5 M
0.125 M Na3PO4 (aq)
Effective molarity = 0.5 M
Hence, all colligative properties are same
