Imagine yourself working in a biochemistry lab, where you have discovered that Arginine has some wonderful health benefits, but there are some major drawbacks depending on which form of the amino acid is present.

• 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 0.01M, you must make a decision about the appropriate pH at which a dosage would be given.

You must answer the following; 1) What pH is the solution when it first dissolves?

2) What is the highest pH that you could use without risking toxic effects?
Graphs that illustrate your answers are very powerful!
The following pKa's for Arginine are useful;

pK₁=1.823 pK₂=8.991 pK₃=12.48
The fully protonated form may be expressed this way; H₃L²⁺

• Your laboratory technician was trying to find the pKa for a weak acid and titrated with 0.0021M NaOH, but you can tell that the curve is wrong because you know that the

    pKa = 4.6. The technician insists that the titration was correct. You prove that it was      incorrect by reproducing the curve on a spreadsheet graph. You find that you are working with a chemical illiterate when the tech says that it must have been a diprotic system, so you reproduce a diprotic titration using pK₁ = 4.78 and pK₂ = 9.97.

• a. Use systematic treatment of equilibria to derive the fractional composition of each component of a tetraprotic system.

b. Derive the Henderson-Hasselbach equation from the weak acid equilibrium expression. (Hint- no substitutions are necessary)

Now create a table that shows how pH changes as the ratio of conjugate base/acid changes. Use numbers like 100:1, 75:1, -> 1:100. 
Finally, find the pH of a solution prepared by dissolving 12.43g tris buffer FW 121.14(B) and 4.67g tris hydrochloride FW 157.60 (BH+) in 1.00L water.