Homework 2 - chapter 1 problems

Biochemistry Homework 2                                                            Fall 2013

 Due Tuesday, 9/10/13

Part 1. Geckos can hang upside down on a polished glass surface. But there’s debate about what kinds of non-covalent interactions allow geckos to perform this feat. Are dispersion (London) forces alone sufficient to explain the gecko’s ability to cling like spiderman? What do the authors of the following article have to say about this question? Find the article, glean a few nuggets from the Introduction and Conclusion, and let me know what you think.

Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements.

Published online before print October 31, 2005, doi: 10.1073/pnas.0506328102.
PNAS November 8, 2005 vol. 102 no. 45 16293-16296



Part 2.  You must show all of your calculations.


1. What is the pH of a solution with the following H+ concentration?

            a. [H+] = 6 x 10-4

            b. [H+] = 12.5 x 10-7


2. What is the pH of the following solutions?                       

            a. 0.2 M hydrochloric acid (VERY strong acid)

            b. an acetic acid solution at 50% dissociation

            c. a solution of O.1 M NaOH (VERY strong base)


            (Ka of acetic acid is 1.74 x 10-5)


3. What is the hydrogen ion concentration of solutions with the following pH?

            a. 10.1

            b. 3.6


4. What would be the pH of a solution containing 0.25 M acetic acid and 0.25 M sodium acetate?


5. Calculate the pKa of lactic acid given that when the concentration of lactic acid is 0.01 M and the concentration of lactate is 0.087 M, the pH is 4.8.


6. Calculate the ratio of the concentrations of acetate and acetic acid required in a buffer system of pH 5.3.


7. Aspirin is a weak acid with a pKa of 3.5. It is absorbed into the blood through the cells lining the stomach and small intestine. Absorption requires passage through the plasma membrane, the rate of which is determined by the polarity of the molecule:  charged and highly polar molecules pass slowly, whereas neutral hydrophobic ones pass rapidly.

The pH of the stomach contents is about 1.5, and the pH of the contents of the small intestine is about 6. Is more aspirin absorbed into the bloodstream from the stomach or from the small intestine? Please justify your answer.

Also, why do you think some aspirin is sold as “buffered” aspirin?

Last modified: Wednesday, September 4, 2013, 9:31 PM