Chem 101B Problem Set #4
Due at Exam #2; 3/10/2010
1. Why is the end point of a titration of acetic acid and potassium hydroxide somewhat basic?
2. Calculate the pH of the following solutions:
a) 0.0001 M benzoic acid, pKa = 4.20.b) The solution resulting from mixing 500 mL of 0.04 M formic acid with 500 mL of 0.01 M NaOH. pKa for formic acid is 3.75.
3. Prove that for a di-protic acid the [A2-] = K 2 when the pure H2A is dissolved in pure water.
4. Consider 100 mL of 0.1 M H2A. Assume that H2A is a diprotic acid with pK1 = 4 and pK2 = 7. You will titrate this acid with 0.1 M NaOH.
a) What volume of the NaOH must be added to maximize the concentration of HA-?b) What is the pH of the solution in part (a)?
c) What is the pH of the initial solution of H2A after only 30 mL of the NaOH have been added? What is the major species of H2A in this solution?
d) What is the pH of the initial solution of H2A after 150 mL of NaOH have been added? What is the major species of H2A in this solution?
5. Sodium benzoate is the conjugate base of benzoic acid and it is used as a food preservative. How would you make a buffer solution based on this system to have a pH = 5.0?
6. What part of the titration curve of a weak acid corresponds to the buffer region? Explain.
7. Calcium carbonate is sparingly soluble in neutral water. Write out the equation for what is involved. Why doesn't an increase in the quantity of calcium carbonate increase its solubility? What units is solubility measure in?8. Consider the slightly soluble salt Lead Iodide.
a) It is found that the solubility of PbI2 is 1.2 X 10-3 mole per liter at 298 °K. What is the Ksp for PbI2?b) What is the solubility of PbI2 in a 1.0 x 10-2 M Pb(NO3)2 solution?
(If you do not obtain a Ksp for part (a), assume that Ksp = 1.0 x 10-10.)
c) What do you think will happen to the solubility of PbI2 in part (a) if the temperature is increased? What data would you need, to be sure of your answer?
Chapter 8 Problems: 74, 100 and TRY 152 ( Wow! This is a great one to workon )
5th Ed. => 66 and 86 and 139 ( Wow! This is a great one.)
There are many good to excellent problems at the end of Chpt 8. Try them, and if you have questions come see me! =)Solution Key- now available - don't peek until you try them... ;-)
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