Exam III

CHM336

Dr. Foy

The rules for this exam are the same as the last. The text and other books are only to be used as reference books. You MUST work independently. You are on your honor to abide by these rules.

As this course begins to wind down, you are all facing the possibility of summer internships, graduate school, or perhaps a job! This exam will put you in various laboratory positions.

1. Your first lab does a lot of acid-base work and are constantly calculating various species concentrations. Use systematic treatment of equilibria to find the concentrations of all species in a 0.10M solution of acetic acid.

2. Still in the same lab, you are now given a little more complex problem. You now need to calculate the equilibrium concentrations of all the species in solution of AgCl in 0.010MNH₃. Don’t neglect the silver ammonia complexes.

3. Now we move to the biochem lab where they use a lot of buffers. You start off with this problem;

There are two flasks, one containes 100mL of pure water pH=7.00, and the other is 100mL of a solution containing 10mmol of HA, pKa = 7.00, and 10mmol of the conjugate base A-. The pH of this solution is also 7.00. To each flask is added 1.00mmol solid NaOH. Calculate the pH of the resulting solution and the change in pH.

4. Still in the biochem lab, you must first find the TRIS buffer in a reference book, and then produce a graph that shows how a 0.01M solution of the buffer changes with the addition of acid (0.0010M) and then the addition of base(0.0010M).

5. One last problem before leaving the biochem lab just to leave a lasting impression, you derive the Henderson Hasselbach equation using the BASE dissociation equation (Kb).

6. Your final seminar topic in front of all of the lab groups is fractional composition.

a. You start by deriving the fractional composition of each of the possible species in a solution of phosphoric acid.

b. Now use these derivations to find the concentration of each species in 0.0133M solution at pH = 2.5, 3.15, 5.33, 7.95, 10.01.

7. Now show the fraction of each species in graphical form as the pH is changed.