(a) Illustrate a titration curve of the following structure. (Solid lines indicate covalent bonds) Indicate buffering regions (including size) and the isoelectric point, pl. Asn - Cys - Ala Lys-Cys - Phe (b) What is the predominant charge state at the following pH values? pH I, pH 4, pH 7, pH 11 (c) What would you expect to happen to your titration curve if you exposed this peptide to Beta- mercaptoethanol prior to titration? Describe the changes in the titration curve.

(a) Illustrate a titration curve of the following structure. (Solid lines indicate covalent bonds) Indicate buffering regions (including size) and the isoelectric point, pl. Asn - Cys - Ala Lys-Cys - Phe (b) What is the predominant charge state at the following pH values? pH I, pH 4, pH 7, pH 11 (c) What would you expect to happen to your titration curve if you exposed this peptide to Beta- mercaptoethanol prior to titration? Describe the changes in the titration curve.

Chemistry: Principles and Reactions

8th Edition

ISBN:9781305079373

Author:William L. Masterton, Cecile N. Hurley

Publisher:William L. Masterton, Cecile N. Hurley

Chapter14: Equilibria In Acid-base Solutions

Section: Chapter Questions

Problem 37QAP: Given three acid-base indicatorsâ€”methyl orange (end point at pH 4), bromthymol blue (end point at...

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Given three acid-base indicatorsâ€”methyl orange (end point at pH 4), bromthymol blue (end point at pH 7), and phenolphthalein (end point at pH 9)â€”which would you select for the following acid-base titrations? (a) perchloric acid with an aqueous solution of ammonia (b) nitrous acid with lithium hydroxide (c) hydrobromic acid with strontium hydroxide (d) sodium fluoride with nitric acid
2. You are studying an unusual enzyme that produces hydronium ions (H3O+) during the courseof the reaction.You wish to maintain pH = 8.5 for the enzyme-catalyzed reaction. Which weak acid will serveas the better 0.1 M buffer for the reaction: HEPPS with pKa = 8.0, or, AMPSO with pKa = 9.0?Justify your answer by describing how the buffer “resists” change in pH and the chemical logicof why you chose the buffer you did.
Many chemical reactions are carried out in the presence of buffers. Use the Henderson-Hasselbalch equation to provide a recommendation for a suitable acete/acetic acid buffer under the following reaction conditions. a) If a checial reaction produces hydroxide ion, OH-, what would be the range for the target pH of a buffer soution that would favor pH stabilizatoin under these conditions? Explain.
b. A student has a sea water sample which contains Ca2+ ions . Describe briefly how he willdetermine the concentration of Ca2+ ion in the sample using a simple titration. Explain the colourchanges at the endpoint. Which medium is suitable for performing the titration, acidic or basic medium and why?
Suppose someone did not put enough 3M HCl in a beaker and conducted a filtration of the cloudy suspension when the pH was 4 rather than 2. A very low yield of product was obtained after drying and filtration of the solid. Suggest possible reasons for this lower yield.
An approximately 0.1-molar solution of NaOH is to be standardized by titration. Assume that the following materials are available. Clean, dry 50 mL buret •Analytical balance 250 mL Erlenmeyer flask •Wash bottle filled with distilled water Phenolphthalein indicator solution Potassium hydrogen phthalate, KHP, a solid monoprotic acid (to be used as the primary standard) Briefly describe the steps you would take, using the materials listed above, to standardize the NaOH solution. Describe (the set up) the calculations necessary to determine the concentration of the NaOH solution.
1. Describe the amount of reagents and steps needed for the preparation of 100 mL 0.050 M and 0.0050 M Phosphate buffers, both at pH 6.50 using: a. 0.50 M stock Phosphate Buffer solution b. Solid NaH2PO4 · 2H2O and solid Na2HPO4 · 2H2O 2. Write the balanced net ionic equation describing the phosphate buffer system.
You are to prepare 100. mL of an acetate buffer of pH 5.00 using 1.0 M acetic acid (CH3CO2H, also written as HC2H3O2) and solid sodium acetate (NaC2H3O2). To prepare for the investigation, complete the following calculations. The pKa for HC2H3O2 is 4.74. The Henderson-Hasselbach equation is pH = pKa + log ([conjugate base]/[acid]) (a) What ratio of [NaC2H3O2] to [CH3CO2H] is required for a pH = 5.00? (b) You will want the concentrations relatively dilute, so use an acid concentration of 0.10 M. What volume of 1.0 M CH3CO2H would be needed to prepare 100. mL of buffer with the desired concentration of 0.10 M? Use M1V1 = M2V2 (c) Use the ratio from (a) and the concentration desired (discussed in (b)) to calculate how many grams of NaC2H3O2 · 3 H2O would be needed to prepare 100. mL of buffer if the acid concentration is 0.10 M?
Based on the results obtained in the table, What is the color of acid-base indicator B when the pH of the medium is equal to its pKa?
Given aqueous solutions of 0.1 M weak acetic acid (CH3COOH, pKa=4.72) and 0.1 M sodium acetate (NaC2H3O2), calculate the volumes of acid and acetate to be mixed, in order to make 50mL of a buffer solution with pH=5.2.
The desired pH is 6.4 in creating a buffer system/buffer solution of about 50-60mL. Therefore, a student picks Silicic Acid Si(OH)4, as 1mL of 1M of the acid has a pH of 6.4, which also has a pKa of 9.82. What is the ratio HA/A- and ratio A-/HA-? The buffering capacity will be checked by the addition of 1mL of 1M HCl or 1mL of 1M NaOH and should not change by more than 0.25pH units.
If an identical titration is performed with the strong acid HCl, explain why the pH at the equivalence point would be neutral in the case of the HCl titration but not in that of CH3COOH. In order to support the explanations, quote the hypothetical value obtained for the titration of CH3COOH ([CH3COOH] = 0.1082 mol/L at equilibrium) and identify the species present at the equivalence point for the 2 acids.