Lab Shedule
Lab 01
Lab 02
Lab 03
Lab 04
Lab 05
Lab 06
Lab 07

Cell cycle game

BIO 196 Official Website

pH and Buffers

Exercise A

Read over pages 19 - 21 and understand these points:

• Definition of pH - what is it a measure of?
• The concentration of Hydrogen ions [H+] multiplied by the concentration of Hydroxide ions [OH-] gives the ion product of water. (1 x10^-14)
• When multiplying, add the exponents and when dividing, subtract the exponents.
• Know the pH scale of 0->14
• pH = -log[H+]
• pOH = -log[OH-]
• pH + pOH = 14

The degree of ionization can affect the final molar concentration of an acid or a base. If the molarity of an acid is 1 x 10^-3 and it ionizes 100%, the final solution will also have a concentration of 1 x 10^-3. However, if the degree of ionization is only 10%, an additional step is required to calculate the final concentration. In this case, you need to multiply the original 1 x 10^-3 molarity by 10% or 0.1 - This gives us 1 x 10^-3 multiplied by 0.1 = 1 x 10^-4. Note that the exponent has decreased by one. The same technique works with a degree of ionization of 1%, except that you multiple 1 x 10^-3 by 1% or .01. The final concentration is then 1 x 10^-5.

Exercise B

Normally for this section I would include photos of the cabbage indicators but unfortunately my digital camera is currently out of commission.

Exercise C

Omitted

Exercise D

Omitted

Exercise E

Using the pH meter is pretty self-explanatory and it seems as if no one experienced much difficulty with the device. Perhaps the most important part of this exercise is remembering to calibrate the meter in an acid, neutral, or basic solution depending on your possible unknowns. This gives a much more accurate reading.

Exercise F

The concept of buffers is very important to understand because of their significance in human physiology. For this lab, we had three solutions of unknown buffers. One contained KH2PO4-, another K2HPO4, and a third was a mixture of both (see page 33 for more details). Buffers are unique because they can act as both an acid and a base depending on the situation (this is true only in the third mixture where both chemicals are present). The table on page 34 should look something like this when it is completed:

The thymolphthalein we used was fairly old and I don't believe it changed color in any of the laboratory experiments. According to this chart, Solution A's pH did not change very much when an acid was added (8.4 -> 7.8) while the addition of a base resulted in a jump from 8.4 to 10.8. Therefore, it can be said that Solution A appears to act as a base and it buffers against acids . Moving on to Solution B, the opposite is true. When a base was added the pH changed from 6.0 to 6.3 while the addition of an acid caused a drastic move from 6.0 to 2.8. Therefore, Solution B appears to buffer against bases and it acts as an acid. Finally, upon observation of the results from the third solution, it seems as if neither the addition of an acid or a base changed the pH. We can then safely say that Solution C is a mixture of A & B... it is buffering against both acidic and basic changes . Your body has a solution which is very similar to Solution C - it can account for small changes in both acid and base concentration.

That's about all for this write-up. Have a good week everyone and we'll see you during your lab session.