Titration of Glycine with Na OH PDF

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Freddie Ibarra Biol 3120 Titration of Glycine with NaOH Introduction: The purpose of this experiment was understand the concept of pH and how it is measured, understand the concept of a buffer, how to correctly gather and plot pH data from a titration, define, identify, understand the implications of Pka, and to gain practice correcly using digital pipettors and the pH meters. In this experiment we titratated Glycine an acidic amino acid with NaOH a strong base and determined how many mili liters of 1M NaOH was needed to bring the solution from our starting point of pH 1.49 to 12.

Methods and Materials: 1. Calibrate pH meter by removing probe rinse with DI water and pat dry ( DO NOT RUB) with kim wipe. 2. Place probe in pH 7.0 calibrated buffer 3. Press mode key, device will then say calibrate 4. When it reads the calibration it will say ready and beep when it is done, repeat step 1 5. Same as step 2 but use pH 4.0 calibrated buffer then repeat step 4. 6. Meter should be ready for use 7. Measure pH of .05M HCl and .05M NaOH and calculate what the theoretical amount should be 8. Next place 50 mL of 1.0M Glycine in a 250mL beaker 9. Swirl around in beaker 10. Titrate with 1M NaOH in 2mL increments continue until pH is at or immediately passed 12. Be sure to record pH with every increment of NaOH added 11. Graph titration with pH on y-axis and NaOH added on x-axis, identify how many Pkas there are and what their values are as well as the isoelectric point. 4

Results: See next page for results

Freddie Ibarra Biol 3120

Discussion: On the whole our group worked well together and any source of human error would have been minimal. However, having said that the pH meter that we used of off, for the calibration of pH 7 and ph 4 solution our readouts were 7.84, and 4.8. In addition to this the Ph that we measured for .05M of HCl was.61 and according to my calculations pH = -log(0.5) which equals to pH=.3, This also held true for pH of .05 NaOH which we recorded was 13.41 and has an actual pH of 13.7.

Post Lab Questions: How many Pkas do you detect? We found that there were two Pkas at the beginning and ending points. Why and what reactive groups do you attribute to them? Amino acids have zwitter ions meaning they have two different forms one form at an acidic pH and one at a basic, so when NaOH is added the Glycine is able to give a proton and maintain its acidic pH at first, but once increasing amounts of NaOH are added it becomes harder for it to maintain the pH and it begins to spike rapidly and then increases again at a slow amount. What are the buffering ranges of Glycine? Glycine has an isoelectric point of 5.8, a pka value of 1.952 and pka2 value of 9.8.

Definitions: Buffer: a substance in solution resists changes in pH. Pka: indicates the center of the buffering region of a buffer Isoelectric Point: the pH at which a particular molecule or surface carries no net electrical charge

Based on the table on page 9 of the cell biology lab manual which would be the best buffer for a reaction that is optimal at pH 7.8? MOPES would be the best because its Pka is 7.2 which means in this case its pH at the isoelectric point would be 7.2, buffers work best at ranges +/- 2 which means that it would work best for pH value of 5.2 – 9.2 and 7.8 being in the middle (pH of 7.8 of reaction is only in the mid range of one buffer and that is mopes) of that would make MOPES the best buffer for this reaction.

Find an example of cell biological relevance of pH, include a brief discussion.

Freddie Ibarra Biol 3120 One example of cell biological relevance of pH is how transporters in the plasma membrane regulate cytoslic pH. Most organelles inside the cell require a pH of around 7.2 which is close to physiological pH, in order to keep the pH of the cytosol different antiporters either use energy of stored Na + ions to pump out excess H+ ions from the cell. Or HCO3- is brought in from outside of the cell to absorb the extra H + ion which is the main way the cell will control the pH of the cytosol when it is too low. The H + ions come about in two different ways either by an acid producing reaction inside the cell or it is leaked in. The cell also possess transporters on the cell membrane that will work to pump H+ ions into the cell when the cytosolic pH is too high, because the organelles can only work within a specific point which is about 7.2pH.

Sources: Alberts, Bruce. "Membrane Transport of Small Molecules Ad the Electrical Properties of Membranes." Molecular Biology of the Cell. Sixth ed. New York: Garland Science, 2002. 604-05. Print....