Question

Consider separate solution of $0.500\, M\,C_2H_5OH_{(aq)}, 0.100 \,M \,Mg_3(PO_4 )_2{(aq)}, 0.250\, M \,KBr_{(aq)}$ and $0.125 \,M \, Na_3PO_4$$_{(aq)}$ at $25^{\circ}\,C$. Which statement is true about these solution, assuming all salts to be strong electrolytes?

• A. They all have the same osmotic pressure
• B. $0.100\, M \,Mg_3 \,(PO_4 )_2$$_{(aq)}$ has the highest osmotic pressure
• C. $0.125\, M \,Na_3PO_4$$_{(aq)}$ has the highest osmotic pressure
• D. $0.500\, M\, C_2H_5OH$ $_{(aq)}$ has the highest osmotic pressure

Answer 1

Answer: (A)

$\pi= i\,CRT $

$\pi_{ C _{2} H _{5} OH }=1 \times 0.500 \times R \times T =0.5\, RT $

$\pi_{ Mg _{3}\left( PO _{4}\right)_{2}}=5 \times 0.100 \times R \times T =0.5 \,RT $

$\pi_{ KBr }=2 \times 0.250 \times R \times T =0.5\, RT $

$\pi_{ Na _{3} PO _{4}}=4 \times 0.125 \times RT =0.5\, RT$