Before lab: Do the calculations for the experiments below in your lab notebook. Look up any values needed (mol. wt., pKa, etc.). Review the basics of solution calculations and pH (Boyer ch. 1, 3). Solution Preparation and Dilution 1.

Before lab: Do the calculations for the experiments below in your lab notebook. Look up any values needed (mol. wt., pKa, etc.). Review the basics of solution calculations and pH (Boyer ch. 1, 3). Solution Preparation and Dilution 1. Prepare 80 ml of a 30 mM solution of potassium chloride (KCl) in deionized water (dH2O). 2. Measure and record the conductivity of the solution using the conductivity meter (temp. = 25°C, cell constant = 1). 3. Dilute a portion of your original solution to make 80 ml of a 5 mM KCl solution in dH2O. Measure and record the conductivity of this solution. Buffer Preparation Safety note: Handle glacial acetic acid in the hood. Wear gloves. 1. From sodium acetate (dry), glacial acetic acid, and dH2O, prepare 100 ml of 0.2 M acetate buffer, pH 4.5. 2. Using one of the pH meters, measure and record the pH of the solution. 3. Dilute your acetate buffer to 0.1 M with dH2O, then measure and record the pH again. 2 Calculations and Analyses for Lab Report Reproduce all calculations for the solution and buffer preparations in your lab report, in a clearly readable format. Is the conductivity difference of your two KCl solutions what you would expect given the dilution factor? If not, what is the most likely source of error? How close is the measured pH of your acetate buffer to the target pH (4.5)? What likely sources of error could account for the difference? Compare the pH values of your acetate buffer at 0.2 and 0.1 M. Would you expect these to be the same? Why or why not? 3 Experiment A2: Acid/Base Behavior of Amino Acids and Buffers Amino Acid Titration 1. Obtain a solution of unknown amino acid in water. 2. Measure the pH of the solution. 3. Add 0.25 M HCl in 0.5 ml increments, measuring the pH after each addition. Continue until you are confident that a pKa value for a functional group has been passed. Buffer Titration 1. Obtain a solution of unknown buffer in water. 2. Measure the pH of the solution. 3. Add 0.25 M HCl in 0.5 ml increments, measuring the pH after each addition. Continue until the rate of pH change with HCl addition has increased markedly. Calculations and Analyses for Lab Report Based on your data and the information in Boyer Appendix IV, is your unknown amino acid arginine or glycine? Which of the acid or base functional groups in your amino acid did you titrate with the HCl? Justify your conclusions. How would you expect changes in pH to affect the overall charge of a typical protein? Based on your data, what would be the effective pH range of the buffer you titrated? Justify your conclusion.

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