JEE MAIN - Chemistry (2014 (Offline) - No. 2)
Consider separate solutions 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?
0.125 M Na3PO4(aq) has the highest osmotic pressure.
0.500 M C2H5OH(aq) has the highest osmotic pressure
They all have the same osmotic pressure
0.100 M Mg3(PO4)2(aq) has the highest osmotic pressure.
Explanation
$$\pi = i\,CRT$$
$$^\pi {C_2}{H_3}OH$$
$$ = 1 \times 0.500 \times R \times T = 0.5{\mkern 1mu} RT$$
$${}^\pi M{g_3}{\left( {P{O_4}} \right)_2}$$
$$ = 5 \times 0.100 \times R \times T$$ $$ = 0.5RT$$
$${}^\pi KBr = 2 \times 0.250 \times R \times T = 0.5\,RT$$
$${}^\pi N{a_3}P{O_4} = 4 \times 0.125 \times RT = 0.5\,RT$$
Since the osmotic pressure of all the given solutions is equal.
Hence all are isotonic solution.
$$^\pi {C_2}{H_3}OH$$
$$ = 1 \times 0.500 \times R \times T = 0.5{\mkern 1mu} RT$$
$${}^\pi M{g_3}{\left( {P{O_4}} \right)_2}$$
$$ = 5 \times 0.100 \times R \times T$$ $$ = 0.5RT$$
$${}^\pi KBr = 2 \times 0.250 \times R \times T = 0.5\,RT$$
$${}^\pi N{a_3}P{O_4} = 4 \times 0.125 \times RT = 0.5\,RT$$
Since the osmotic pressure of all the given solutions is equal.
Hence all are isotonic solution.
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