Chemistry 2430 - Quiz #3 - 10 points - Dr. Howard Black - January 26, 2000

1. (2 pts) Provide a brief, accurate definition for the terms below.

a. Lewis acid:      a molecule or ion that accepts an electron pair to form a bond

b. Bronsted-Lowry base:      a molecule or ion that accepts a proton to form a bond
 

2. (3 pts) Formic acid is a Bronsted-Lowry acid, and 
dissociates according to the equation in the box.

a. What is the anion called, as it relates to the acid? 
                        the conjugate base                 
 
b. The pKa of formic acid is 3.7, making it fairly weak. Acetic acid (pKa 4.8) is also relatively weak. Which of these two acids is stronger?           formic acid         Approximately (i.e., don't use a calculator) how many times stronger than the weaker acid is it?       10        [Remember that each pKa unit is a power of 10.]

3. (4 pts) Indicate whether each species below is a Lewis acid (A), Lewis base (B), or neither (N), by writing the appropriate letter on the line underneath each one.


 

4. (1 pt) The pKa's of three popular pain-relievers are listed below. Which one should you take if you have problems with acid indigestion (which is caused by the stomach contents being too acidic)?

answer:        acetaminophen

acetaminophen (Tylenol7) pKa = 9.9

aspirin pKa = 3.5

ibuprofen pKa = 5.2