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PCHEM Workshop 8 Notes

Updated: Dec 30, 2019

Eighth workshop with Dineli for Physical Chemistry (CHEM 3321) with Dr. Nielsen at UT Dallas!

To anyone reviewing my notes: Please feel free to reach out if you need any clarification on anything I wrote — but if I’m completely honest, I’ve got a ton going on with school, work, and life so I may or may not get back to you in a timely manner. Doing my best, here!

If you want to contact me for more information/ any clarification/ to start a study group/ need talk to someone… please comment below, DM me on Instagram, or send an email by clicking this link, the icon in the top right corner, or manually typing out

WORKSHOP WITH DINELI | October 29, 2019

Be sure to check Dineli’s page for her notes online. These are not the complete answers for the problem set. Make sure you plug and chug to get the individual answers! Also, verify any answers shown here — Dineli always stresses that we should verify the calculations from workshop!

Problem 1 Water boils at 373.15 K with ∆Hvap = 40.656 kJ/mol. Water freezes at 273.15 K with ∆Hfus = 6.008 kJ/mol. Benzene boils at 353.2 K with ∆Hvap = 30.8 kJ/mol. Benzene freezes at 278.61 K with ∆Hfus = 10.59 kJ/mol. From these data, calculate the freezing point depression constant, and the boiling point elevation constant, for both water and benzene. Express your answer in units of K kg mol−1 which is Kelvin / molal.

Problem 2 The total vapor pressure of a 4 mol % solution of NH3 in water is 50.00 mm Hg at 20 ◦C; the vapor pressure of pure water is 17.00 mm Hg at this temperature. Apply Henry’s and Raoult’s laws to calculate the two partial pressures and the total vapor pressure of a 5 mol % solution.

Problem 3 Pure water is saturated with a 2:1 mixture of hydrogen and oxygen gas at a total pressure of 5 atm at 298 K. The water is then boiled to remove all the gases. Calculate the % composition of the gases driven off (after drying). (kH(O2) = 4.95 × 104 bar; kH(H2) = 8.23 × 104 bar near 25 ◦C)

Problem 4 A solution of sucrose in water freezes at -0.200 ◦C. Calculate the vapor pressure of this solution at 25 ◦C (accurate to 0.001 mm Hg). The vapor pressure of pure water at 25 ◦C is 23.506 mm Hg and the molal freezing-point constant for water is 1.86 ◦C/m.

Problem 5 Calculate the osmotic pressure of a 2 molal aqueous solution of sucrose at room temperature assuming ideal (Raoult’s Law) behavior. Compare to the value of π = 58.0 atm which accounts for non-ideal behavior.

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