EXAM III
CHM 333

You must complete this exam on your own and may use reference material including notes and your book and clarification of questions by me!

I am sorry that this is posted late, but sampling took precedence, and I did say 12:00 but did not specify am or pm!!

This Exam is due Tuesday September 16, 1999 by 5:00pm.


 
 

Imagine yourself as the director of an upstart biochemistry lab, where you have discovered that Tyrosine is highly therapeutic, but there are some major drawbacks depending on which form of the amino acid is present.

1.    a.  You start by calculating the fractional composition of each species at a variety of pH
            values. Produce a graph that shows the different compositions at different pH values.
        b. Assuming a Formal concentration of 0.15M, you must make a decision about the
            appropriate pH at which a dosage would be given.
            Here is the situation;

1) The injection is a 2cc dose
2) The therapeutic species is the unprotonated form
3) The species you must start with is the triprotic form
4) The fully diprotic form is toxic at levels of 1x10-8M                 You must answer the following;

                1) What pH is the solution when it first dissolves?
                2) What is the lowest pH that you could use without risking toxic effects?
                3) Will tyrosine be effective at normal body's pH?

                You need to use the fractional composition graph to justify your answers.

2.     Your best customer has had very little chemistry but is in need of analysis of some
        unknown acids.

a.     You find that 2.0g of the first acid has a single pKa of 4.3, and it takes 50.0mL of
        0.10M NaOH to reach the endpoint. Create a graph of the titration curve for you
        customer and determine the Molecular weight of the acid.   b.     0.5g of the second acid is a triprotic system with a pKa1 = 2.7, pKa2 = 5.3, and a
        pKa3 = 9.1. If it takes 43mL of 0.05M NaOH to reach the last enpoint, reproduce the
        titration graph, and calculate Molecular weight of the acid. 3.     a.     Use systematic treatment of equilibria to derive the fractional composition of each
                component of a triprotic system. b.     Derive the Henderson-Hasselbach equation from the weak acid equilibrium
        expression.   c.     Now create a table that shows how pH changes as the ratio of conjugate base/acid changes. Use numbers like 100:1, 75:1, B> 1:100.
  d.     Finally, find the pH of a solution prepared by dissolving 13.5g TRIS buffer FW 121.14(B) and 12.67g TRIS hydrochloride FW 157.60 (BH+) in 1.00L water.