Recitation before exam-student
2
Elise Myers; 5.111 TA Fall 2012 I. Warmup The pKa of HIO (aq) is 10.64 and that of HIO 3(aq) is 0.77. Account for the difference in acid strength. II. Test Suggestions Prof. Klibanov is writing the test (study the problem sets!) No review sheets will be generated (make your own) Office hours will be held this weekend: ______ One practice test posted- this is your best study guide Understand how the lecture material applies to the problem sets III. Practice! 1. Calculate the pH, pOH, and percentage of deprotonation of the given aqueous solutions a) 0.20 M CH 3 COOH (aq) b) 0.20M CCl 3 COOH(aq) c) 0.20 M HCOOH(aq) (do on own time) 2. The standard entropy of vaporization of benzene is approximately 85 J/Kmol at its boiling point. a) Estimate the standard enthalpy of vaporization of acetone at its normal boiling point of 56.2*C b) What is the standard entropy change of the surroundings when 10. g of acetone CH 3 COCH 3 condenses at its normal boiling point?
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Transcript of Recitation before exam-student
Elise Myers; 5.111 TA Fall 2012
I. Warmup
The pKa of HIO(aq) is 10.64 and that of HIO3(aq) is 0.77. Account for the difference in
acid strength.
II. Test Suggestions
Prof. Klibanov is writing the test (study the problem sets!)
No review sheets will be generated (make your own)
Office hours will be held this weekend: ______
One practice test posted- this is your best study guide
Understand how the lecture material applies to the problem sets
III. Practice!
1. Calculate the pH, pOH, and percentage of deprotonation of the given aqueous
solutions
a) 0.20 M CH3COOH(aq)
b) 0.20M CCl3COOH(aq)
c) 0.20 M HCOOH(aq) (do on own time)
2. The standard entropy of vaporization of benzene is approximately 85 J/Kmol at its
boiling point.
a) Estimate the standard enthalpy of vaporization of acetone at its normal boiling
point of 56.2*C
b) What is the standard entropy change of the surroundings when 10. g of
acetone CH3COCH3 condenses at its normal boiling point?
Elise Myers; 5.111 TA Fall 2012
3. Which would you expect to have a higher molar entropy at T=0, single crystals of
BF3 or of COF2? Why?
4. Without performing any calculations, predict whether there is an increase or a
decrease in entropy for each of the following processes:
a) Cl2(g) + H2O(l) HCl (aq) + HClO(aq)
b) Cu3(PO4)2(s) 3Cu2+
(aq) + 2PO4-3
(aq)
c) SO2(g) + Br2(g) + 2H2O(l) H2SO4(aq) + 2HBr(aq)
5. Benzene has a vapor pressure of 94.6 Torr at 25*C. A nonvolatile compound was
added to 0.300 mol benzene (l) at 25*C and the vapor pressure of the benzene in
the solution decreased to 75.0 Torr. What amount (in moles) of solute molecules
was added to the benzene?
6. Colligative properties can be sources of insight into not only the properties of
solutions, but also the properties of the solute. For example, acetic acid
CH3COOH, behaves differently in two different solvents.
a) The freezing point of a 5.00% by mass aq solution of acetic acid is -1.72*C.
What is the molar mass of the solute? Explain any discrepancy between the
experimental and expected molar mass.
b) The freezing point depression associated with a 5.00% by mass solution of
acetic acid in benzene is 2.32 *C. What is the experimental molar mass of the
solute in benzene? What can you conclude about the nature of acetic acid in
benzene?
