Do colligative properties depend on the number of solute molecules? Colligative properties are properties that are affected by the number of solute molecules dissolved in the solution. True or false?


I think the statement is false, and the correct one should use "number of solute particles". I asked my TA and he said the molecule version is true, although I show him an example that $\ce{H2CO3}$ can dissolve water in many ways to create different sets of miles for $(\ce{CO3^2-},$ $\ce{HCO3-},$ $\ce{H+}).$ In this case, one mole of molecules $(\ce{H2CO3})$ can result in different total numbers of particles.

However, my TA said that $\ce{CO3^2-},$ $\ce{HCO3-},$ and $\ce{H+}$ can be considered as different molecules. I still don't satisfy with his answer though. 

Could someone explain it for me, whether I am right or wrong.
It's not good notation on the TAs part. IUPAC defines a molecule as having to be electrically neutral. I see what they are intending, but solute particles would be more correct. This is why, as you noted, compounds that dissolve into ions produce a greater effect than the number of original molecules would suggest and molecules that aggregate in solution have a smaller effect. Equations for colligative properties depend on the van't Hoff factor, which essentially converts from the original number of molecules to the number of distinct particles.