In an acid-base titration between CH2O2 (formic acid) and NaOH, theequivalence point occurs when _______________ while the end point occurswhen _______________.

In an acid-base titration between CH2O2 (formic acid) and NaOH, theequivalence point occurs when _ while the end point occurswhen _.

Chemistry: Matter and Change

1st Edition

ISBN:9780078746376

Author:Dinah Zike, Laurel Dingrando, Nicholas Hainen, Cheryl Wistrom

Publisher:Dinah Zike, Laurel Dingrando, Nicholas Hainen, Cheryl Wistrom

Chapter18: Acids And Bases

Section: Chapter Questions

Problem 87A: When might a pH meter be better than an indicator to determine the end point of an acid-base...

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When might a pH meter be better than an indicator to determine the end point of an acid-base titration?
What is an acidbase indicator? Define the equivalence (stoichiometric) point and the end point of a titration. Why should you choose an indicator so that the two points coincide? Do the pH values of the two points have to be within 0.01 pH unit of each other? 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 of weak base is titrated to the equivalence point with a strong acid. Which one of the following statements is most likely to be correct? a The pH of the solution at the equivalence point is 7.0. b The pH of the solution is greater than 13.0. c The pH of the solution is less than 2.0. d The pH of the solution is between 2.0 and 7.0. e The pH of the solution is between 7.0 and 13.0. The reason that best supports my choosing the answer above is a Whenever a solution is titrated with a strong acid, the solution will be very acidic. b Because the solution contains a weak base and the acid (titrant) is used up at the equivalence point, the solution will be basic. c Because the solution contains the conjugate acid of the weak base at the equivalence point, the solution will be acidic.
A friend asks the following: Consider a buffered solution made up of the weak acid HA and its salt NaA. If a strong base like NaOH is added, the HA reacts with the OH to form A. Thus the amount of acid (HA) is decreased, and the amount of base (A) is increased. Analogously, adding HCI to the buffered solution forms more of the acid (HA) by reacting with the base (A). Thus how can we claim that a buffered solution resists changes in the pH of the solution? How would you explain buffering to this friend?
A student intends to titrate a solution of a weak monoprotic acid with a sodium hydroxide solution but reverses the two solutions and places the weak acid solution in the buret. After 23.75 mL of the weak acid solution has been added to 50.0 mL of the 0.100 M NaOH solution, the pH of the resulting solution is 10.50. Calculate the original concentration of the solution of weak acid.
Another way to treat data from a pH titration is to graph the absolute value of the change in pH per change in milliliters added versus milliliters added (pH/mL versus mL added). Make this graph using your results from Exercise 61. What advantage might this method have over the traditional method for treating titration data?
Consider all acid-base indicators discussed in this chapter. Which of these indicators would be suitable for the titration of each of these? (a) NaOH with HClO4 (b) acetic acid with KOH (c) NH3 solution with HBr (d) KOH with HNO3 Explain your choices.
Determine the dominant acid-base equilibrium that results when each of the following pairs of solutions is mixed. Indicate the equilibrium by writing 1 for a strong acid, 3 for a weak acid, 4 for an acidic buffer, 7 for a neutral solution, 10 for a basic buffer, 11 for a weak base, and 13 for a strong base. (a) 10.0 mL of 0.15 M NaOH + 15.0 mL of 0.10 M HNO3 (b) 25.0 mL of 0.10 M HCl + 10.0 mL of 0.25 M NH3 (c) 50.0 mL of 0.050 M NaOH + 50.0 mL of 0.10 M NH3 (d) 50.0 mL of 0.10 M NH3 + 50.0 mL of 0.05 M HCl
You are given the following acidbase titration data, where each point on the graph represents the pH after adding a given volume of titrant (the substance being added during the titration). a What substance is being titrated, a strong acid, strong base, weak acid, or weak base? b What is the pH at the equivalence point of the tiration? c What indicator might you use to perform this titration? Explain.
Follow the directions of Question 64. Consider two beakers: Beaker A has a weak acid(K a=1105). Beaker B has HCI. The volume and molarity of each acid in the beakers are the same. Both acids are to be titrated with a 0.1 M solution of NaOH. (a) Before titration starts (at zero time), the pH of the solution in Beaker A is the pH of the solution in Beaker B. (b) At half-neutralization (halfway to the equivalence point), the pH of the solution in Beaker A the pH of the solution in Beaker B. (c) When each solution has reached its equivalence point, the pH of the solution in Beaker A the pH of the solution in Beaker B. (d) At the equivalence point, the volume of NaOH used to titrate HCI in Beaker B the volume of NaOH used to titrate the weak acid in Beaker A.
Sulfanilic acid (NH2C6H4SO3H) is used in manufacturing dyes. It ionizes in water according to the equilibrium equation NH2C6H4SO3H(aq)+H2O(l)NH2C6H4SO3(aq)+H3O+(aq)Ka=5.9104 A buffer is prepared by dissolving 0.20 mol of sulfanilicacid and 0.13 mol of sodium sulfanilate (NaNH2C6H4SO3) in water and diluting to 1.00 L. Compute the pH of the solution. Suppose 0.040 mol of HCl is added to the buffer.Calculate the pH of the solution that results.