PRE-LAB QUESTIONS 1. What is a zwitterion? What is a molecule\'s isoelectric poi

Question

PRE-LAB QUESTIONS 1. What is a zwitterion? What is a molecule's isoelectric point? (use your Google skill)What is the isoelectric point for p-aminobenzoic acid and the pKa of benzocaine? 2. In this experiment, which compound is in excess; p-aminobenzoic acid or ethanol? How is the yield of the product expected to be affected by the excess of this reagent? Explain your reasoning. 3. Write the mechanism for the Fischer esterification of p-aminobenzoic acid with ethanol (the second reaction on the previous page What is the solubility (in units of g/mL) of benzocaine in water? Is benzocaine soluble in any other solvents? (hint: the Merck index can be quite useful) 4. 5. Which solid substance used over the course of this experiment could potentially contaminate your dry benzocaine product, but would not be expected to show up on a TLC plate under UV light?

Explanation / Answer

(1)

a zwitterion is a neutral molecule with a positive and a negative electrical charge, distinct from dipoles, at different locations within that molecule.

The isoelectric point (pI), sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge.

isoelectric point of p-aminobenzoic acid at a pH-value of about 3.72(approx 4), and benzocaine will have no isoelectric point.

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