Here's the final review questions for the final exam. Remember that the packet must be totally completed for credit and must be handwritten. Don't forget to study your organic notes even though it's not on the study guide.
Please read the following introductory information for AP Chemistry and complete the assignment for summer. You will find reference PowerPoint’s, links to tutorials, etc. on the left side of Mrs. Pierce’s blog, http://lhsblogs.typepad.com/pierce/ .
Also, use Brown- Lemay Chemistry text (issued by Lassiter) or 5 steps to a 5 or a Princeton AP Chemistry Review book, which can be purchased locally or online.
Week of April 29 - weekend homework - Download Practice Final Exam ( it's a pdf file, so on my computer you need to click the refresh updown arrow by the URL space) - try this practice exam over the weekend. Record your answers on a sheet of paper to turn in on Monday. (you do not need to print out this exam - save paper and ink)
I thought you might be interested in how the human body works with it's own buffering system.
This figure shows the major organs that help control the blood concentrations of CO2 and HCO3-, and thus help control the pH of the blood.
Removing CO2 from the blood helps increase the pH. Removing HCO3- from the blood helps lower the pH.
The Carbonic-Acid-Bicarbonate Buffer in the Blood
By far the most important buffer for maintaining acid-base balance in the blood is the carbonic-acid-bicarbonate buffer. The simultaneous equilibrium reactions of interest are
The carbonic acid-bicarbonate buffer is a solution of carbonic acid and bicarbonate ions. When a base is added to this buffer, it reacts with the carbonic acid to produce neutral water. The pH changes very little.
H2CO3 + OH- → HCO3- + H2O
We are interested in the change in the pH of the blood; therefore, we want an expression for the concentration of H+ in terms of an equilibrium constant (see blue box, below) and the concentrations of the other species in the reaction (HCO3-, H2CO3, and CO2).
To more clearly show the two equilibrium reactions in the carbonic-acid-bicarbonate buffer, Equation 1 is rewritten to show the direct involvement of water:
The equilibrium on the left is an acid-base reaction that is written in the reverse format from Equation 3. Carbonic acid (H2CO3) is the acid and water is the base. The conjugate base for H2CO3 is HCO3- (bicarbonate ion). Carbonic acid also dissociates rapidly to produce water and carbon dioxide, as shown in the equilibrium on the right of Equation 10. This second process is not an acid-base reaction, but it is important to the blood's buffering capacity, as we can see from Equation 11, below.
As shown in Equation 11, the pH of the buffered solution (i.e., the blood) is dependent only on the ratio of the amount of CO2 present in the blood to the amount of HCO3-(bicarbonate ion) present in the blood (at a given temperature, so that pK remains constant). This ratio remains relatively constant, because the concentrations of both buffer components (HCO3- and CO2) are very large, compared to the amount of H+ added to the blood during normal activities and moderate exercise. When H+ is added to the blood as a result of metabolic processes, the amount of HCO3- (relative to the amount of CO2) decreases; however, the amount of the change is tiny compared to the amount of HCO3- present in the blood. This optimal buffering occurs when the pH is within approximately 1 pH unit from the pK value for the buffering system, i.e., when the pH is between 5.1 and 7.1.
However, the normal blood pH of 7.4 is outside the optimal buffering range; therefore, the addition of protons to the blood due to strenuous exercise may be too great for the buffer alone to effectively control the pH of the blood. When this happens, other organs must help control the amounts of CO2 and HCO3- in the blood. The lungs remove excess CO2 from the blood (helping to raise the pH via shifts in the equilibria in Equation 10), and the kidneys remove excess HCO3- from the body (helping to lower the pH). The lungs' removal of CO2 from the blood is somewhat impeded during exercise when the heart rate is very rapid; the blood is pumped through the capillaries very quickly, and so there is little time in the lungs for carbon dioxide to be exchanged for oxygen. The ways in which these three organs help to control the blood pH through the bicarbonate buffer system are highlighted in Figure