CHEM 123N Lecture Notes - Lecture 9: Boiling Point, Osmotic Pressure, Molality

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ultramarinebee844

12 Nov 2018

School

Old Dominion University

Department

Chemistry And Biochemistry

Course

CHEM 123N

Professor

John Donat

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Document Summary

Depend only on quantity of solute, not identity / chemical composition. Vapor pressure o(cid:257) (cid:376)olatile sol(cid:376)e(cid:296)t o(cid:376)er a solutio(cid:296) = sol(cid:376)e(cid:296)t"s (cid:295)ole fraction * pure solvent vapor pressure. Solutions of ionic substances often have a vapor pressure significantly lower than predicted because the mole fraction of the solvent includes total concentration of solute ions instead of formula units. If the solute to solvent forces are weak, the solvent is less tightly held in solution, and actual p soln is (cid:258)reater tha(cid:296) raoult"s predicted p sol(cid:296). P soln - vapor pressure of solution / pressure of solution. If the forces are strong, the solvent is more tightly held in solution, and the actual p sol(cid:296) < raoult"s predicted p sol(cid:296). But - ion dipole forces between dissolved ions and polar water molecules are very strong and form ion pairs. Vapor pressure is si(cid:258)(cid:296)i(cid:257)ica(cid:296)tly lo(cid:377)er tha(cid:296) raoult"s la(cid:377) predicts. Va(cid:296)"t ho(cid:257)(cid:257) factor (cid:706)i(cid:707) : actual de(cid:258)ree o(cid:257) dissociatio(cid:296).

Related Questions

Vapor-pressure lowering is a colligative property, as are freezing-point depression and boiling-point elevation. What is a colligative property? Why is the freezing point depressed for a solution as compared to the pure solvent? Why is the boiling point elevated for a solution as compared to the pure solvent? Explain how to calculate ∆T for a freezing-point depression problem or a boiling-point elevation problem. Of the solvents, which would have the largest freezing-point depression for a 0.50 molal solution? Which would have the smallest boiling-point elevation for a 0.50 molal solution? A common application of freezing-point depression and boiling-point elevation experiments is to provide a means to calculate the molar mass of a nonvolatile solute. What data are needed to calculate the molar mass of a nonvolatile solute? Explain how you would manipulate these data to calculate the molar mass of the nonvolatile solute.