This question concerns part 1 of this lab. You need to make a buffer solution by mixing both a weak acid and its conjugate base in the right proportions to achieve the desired pH. Your desired target pH is 4.20. You have been provided with 5.00 mL of 0.100 M sodium acetate solution. How many moles of acetic acid do you need to add to this solution to obtain a buffer solution at the desired pH? The pKa of acetic acid is 4.74.

This question concerns part 1 of this lab. You need to make a buffer solution by mixing both a weak acid and its conjugate base in the right proportions to achieve the desired pH. Your desired target pH is 4.20. You have been provided with 5.00 mL of 0.100 M sodium acetate solution. How many moles of acetic acid do you need to add to this solution to obtain a buffer solution at the desired pH? The pKa of acetic acid is 4.74.

Chemistry: An Atoms First Approach

2nd Edition

ISBN:9781305079243

Author:Steven S. Zumdahl, Susan A. Zumdahl

Publisher:Steven S. Zumdahl, Susan A. Zumdahl

Chapter13: Acids And Bases

Section: Chapter Questions

Problem 191MP

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. The concepts of acid-base equilibria were developed in this chapter for aqueous solutions (in aqueous solutions, water is the solvent and is intimately involved in the equilibria). However, the Brønsted-Lowry acid-base theory can be extended easily to other solvents. One such solvent that has been investigated in depth is liquid ammonia. NH3. a. Write a chemical equation indicating how HCl behaves as an acid in liquid ammonia. b. Write a chemical equation indicating how OH- behaves as a base in liquid ammonia.
Each box represents an acid solution at equilibrium. Squares represent H+ ions. Circles represent anions. (Although the anions have different identities in each figure, they are all represented as circles.) Water molecules are not shown. Assume that all solutions have the same volume. (a) Which figure represents the strongest acid? (b) Which figure represents the acid with the smallest Ka? (c) Which figure represents the acid with the lowest pH?
Two students were asked to determine the Kb of an unknown base. They were given a bottle with a solution in it. The bottle was labeled aqueous solution of a monoprotic strong acid. They were also given a pH meter, a buret, and an appropriate indicator. They reported the following data: volume of acid required for neutralization = 21.0 mL pH after 7.00 mL of strong acid added = 8.95 Use the students' data to determme the Kb of the unknown base.
You have a solution of the weak acid HA and add some HCl to it. What are the major species in the solution? What do you need to know to calculate the pH of the solution, and how would you use this information? How does the pH of the solution of just the HA compare with that of the final mixture? Explain.
Methyl orange, HMO, is a common acid-base indicator. In solution it ionizes according to the equation: HMOaqH+aq+MO-aqredyellow If methyl orange is added to distilled water, the solution turns yellow. If 1 drop or two of 6 M HCl is added to the yellow solution, it turns red. If to that solution one adds a few drops of 6 M NaOH, the color reverts to yellow. a. Why does adding 6 M HCl to the yellow solution of methyl orange tend to cause the color to change to red? Note that in solution HCl exists as H+ and Cl- ions. b. Why does adding 6 M NaOH to the red solution tend to make it turn back to yellow? Note that in solution NaOH exists as Na+ and OH- ions. How does increasing OH- shift Reaction 3 in the discussion section? How would the resulting change in H+ affect the dissociation reaction of HMO?
A solution has a pH of 4.5. What would be the color of the solution if each of the following indicators were added? (See Fig. 14-8.) a. methyl orange b. alizarin c. bromcresol green d. phenolphthalein
Composition diagrams, commonly known as alpha plots, are often used to visualize the species in a solution of an acid or base as the pH is varied. The diagram for 0.100 M acetic acid is shown here. The plot shows how the fraction [alpha ()] of acetic acid in solution, =[CH3CO2H][CH3CO2H]+[CH3CO2] changes as the pH increases (blue curve). (The red curve shows how the fraction of acetate ion, CH3CO2, changes as the pH increases.) Alpha plots are another way of viewing the relative concentrations of acetic acid and acetate ion as a strong base is added to a solution of acetic acid in the course of a titration. (a) Explain why the fraction of acetic acid declines and that of acetate ion increases as the pH increases. (b) Which species predominates at a pH of 4, acetic acid or acetate ion? What is the situation at a pH of 6? (c) Consider the point where the two lines cross. The fraction of acetic acid in the solution is 0.5, and so is that of acetate ion. That is, the solution is half acid and half conjugate base; their concentrations are equal. At this point, the graph shows the pH is 4.74. Explain why the pH at this point is 4 74.
You have a solution of the weak acid HA and add some of the salt NaA to it. What are the major species in the solution? What do you need to know to calculate the pH of the solution, and how would you use this information? How does the pH of the solution of just the HA compare with that of the final mixture? Explain.
Which of the indicators in Fig. 14-8 could be used for the titrations in Exercises 57 and 59?
. Which component of a buffered solution is capable of combining with an added strong acid? Using your example from Exercise 60, show how this component would react with added HC1.
Compare the percent dissociation of the acid in Exercise 21a with the percent dissociation of the acid in Exercise 21d. Explain the large difference in percent dissociation of the acid.
8-71 Explain why you do not need to know the chemical formula of a buffer compound to use it.