Question

Answer the following questions using complete sentences and support your answers with calculations, if desired. Attach additional pages as necessary. Handwritten or typed answers are acceptable. (5 pts per question) 1. Describe in your own words or figures why the addition of non-volatile solutes lower the freezing point of a solvent. 2. If salicylic acid dissociated into two particles when dissolved into myristic acid (it does not), would this change your calculated K value? Explain why. (Hint: look over your notes on the van't Hoff factor, from lecture, for help.) 3. You estimated the freezing point of the salicylic acid-myristic acid solution, during the lab, as lower than it should have been. How would this change your calculated K value versus the true Kr value? Explain why the calculated K value would change 4. Assume that we used a solute with a larger molar mass than salicylic acid, would this change AT compared to the salicylic acid solution? Assume the same solvent is used and molality of the solution is unchanged. Explain why or why not.

Answer 1

Arsa Freezing point is the temperature at which the liquid and the solid states of a substance are in equilibrium with each other we have the same vapour pressure. When the non- volatile solute is added into a pure solvent the freezing point get decreased because the vapour pressure of the solution get decreased If Vapour prestures are plotted against temperatures, the conse CD is obtained for the liquid solvent. At the point D, the liquid solvent starts solidifying and hence the liquid and solid are de equilibrium with each other. Thus, temperature at D is the freezing point of pure solvent. As at every temperature, the vapour pressure of the solution is

ess than that of the pure solvent; the lapous pressure – temperature cone for the solution lies below the pure solvent, represented by AB. As the cooling of the solution is continued at the point E. the separation of the colid colvent starts. Thus, & E is the freezing ppoint of solution. Eure Solvent Vapour pressure Solution MAKAMU Myo Temperature -> Thus, Tf <To To Tf = 4 Tf depression in freezing point) To is freering If is freezing point of point of pure coluent colution
non volatile solutes lower the freezing point of solution.