Highest osmotic pressure

Question

I’d like to ask a question and clear my misunderstanding.

Which of the following 0.01 M solutions have the highest osmotic pressure?
-$\ce{NaCl}$
-$\ce{C12H22O11}$
-$\ce{BaCl2}$
-$\ce{CO(NH2)2}$
-$\ce{[Cr(NH3)4Cl2]Cl}$

I know that the equation for osmotic pressure is
$$\Pi = cRTi$$ I have eliminated sucrose, sodium chloride, and urea from my answer, because sucrose and urea are non-electrolyte. And sodium chloride has smaller van ’t Hoff factor than barium chloride. I ended up in barium chloride and the complex compound. I’m not really sure with the complex compound since from what I learnt, a complex compound is easier to dissolved in water (my teacher in solubility chapter taught me that $\ce{AgI + NH3 -> [Ag(NH3)2]I}$ have a high solubility because it is a complex compound). However I’m not sure if it has a high van ’t Hoff factor as well.

Answer 1

You are correct in thinking that urea and sucrose would have van't hoff factor (i) = 1, since they are non-electrolytes and don't undergo disassociation(or ion pairing).

What you are left with are the following: $\ce{NaCl}$ , $\ce{BaCl_2}$ and $\ce{[Cr(NH_3)_4Cl_2]Cl}$.

Let us begin with the the two chloride salts: $\ce{NaCl}$ , $\ce{BaCl_2}$. we assume 100% disassociation for the two (strong electrolytes) and we have i = 2 and i = 3 respectively for both.

Now, the complex would indeed disassociate but not completely (the extent would be determined $K_f$ for the complex). Thus 1 < i < 2.

Based on this, I believe you can order them on the basis of increasing osmotic pressure.