Question

Explain why the samples with larger amounts of solute precipitated at significantly higher temperatures than those with less solute. Discuss your answer in terms of the physical interaction between the solute and solvent.

Answer 1

Solution:

Solute + Solvent <----------> Solution

the forward process is called Dissolution while the backward process is called Precipitation.These processes keep happening simultaneously in a system and when equilibrium is reached ,the rates of forward and backward processes become equal to each other and no more observable change takes place.Dissolution means ,that the solute particle has diffused into solvent and is now present in solvated form(i.e. surrounded by solvent molecules around it, binded by their attraction energy). Now coming back to the question,if a solvated solute particle in the solution collides with undissolved solute particle, it may stick to its surface leading to crystallisation.As we decreases temperature, the energy of molecule of solvent which surrounds the solvated solute particle decreases and there is higher chance in a solution made from higher amount of dissolved solute of solvated solute particle to overcome the energy of surrounding solvent molecules ,colliding with other undissolved solute particle and crystallising to form precipitate .Thus, a solution containing higher amount of solute forms precipitate at higher temperature.