Textbook Question
You have to prepare a pH = 5.00 buffer, and you have the following 0.10 M solutions available: HCOOH, HCOONa, CH3COOH, CH3COONa, HCN, and NaCN. Which solutions would you use?
Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 34
Compare the titration of a strong, monoprotic acid with a strong base to the titration of a weak, monoprotic acid with a strong base. Assume the strong and weak acid solutions initially have the same concentrations. Indicate whether the following statements are true or false: (b) The pH at the beginning of the titration is lower for the weak acid than the strong acid. (c) The pH at the equivalence point is 7 no matter which acid is titrated.
Verified step by step guidance1
Step 1: Understand the initial pH of the solutions. A strong acid completely dissociates in water, resulting in a higher concentration of hydrogen ions \((\text{H}^+)\), leading to a lower pH. A weak acid partially dissociates, resulting in fewer hydrogen ions and a higher initial pH compared to a strong acid of the same concentration.
Step 2: Analyze the pH at the equivalence point for the titration of a strong acid with a strong base. At the equivalence point, the amount of acid equals the amount of base, and the solution consists of water and the salt formed from the acid and base. For strong acid-strong base titrations, the pH is typically neutral, around 7, because the salt formed does not affect the pH.
Step 3: Consider the pH at the equivalence point for the titration of a weak acid with a strong base. The weak acid forms a conjugate base upon neutralization, which can react with water to produce hydroxide ions \((\text{OH}^-)\), making the solution slightly basic. Therefore, the pH at the equivalence point is greater than 7.
Step 4: Evaluate statement (b): 'The pH at the beginning of the titration is lower for the weak acid than the strong acid.' Based on the dissociation properties of strong and weak acids, this statement is false because the strong acid has a lower initial pH.
Step 5: Evaluate statement (c): 'The pH at the equivalence point is 7 no matter which acid is titrated.' This statement is false because, as explained, the equivalence point pH for a weak acid titration is greater than 7 due to the formation of a basic conjugate base.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Titration Basics
Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant to a solution of analyte until the reaction reaches its equivalence point, where stoichiometrically equivalent amounts of reactants have reacted. The pH changes during the titration can be monitored to understand the nature of the acid-base reaction taking place.
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03:04
Acid-Base Titration
Strong vs. Weak Acids
Strong acids, like hydrochloric acid (HCl), completely dissociate in water, resulting in a higher concentration of hydrogen ions (H+) and a lower pH. In contrast, weak acids, such as acetic acid, only partially dissociate, leading to a higher initial pH compared to strong acids at the same concentration. This difference in dissociation affects the pH at the beginning of the titration and at the equivalence point.
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02:19Weak Acid-Strong Base Titration Curve
Equivalence Point and pH
The equivalence point in a titration is reached when the amount of titrant added is stoichiometrically equivalent to the amount of substance in the solution being titrated. For strong acid-strong base titrations, the pH at the equivalence point is typically 7 due to the complete neutralization of H+ and OH- ions. However, for weak acid-strong base titrations, the pH at the equivalence point is greater than 7 because the resulting solution contains the conjugate base of the weak acid, which can hydrolyze to produce OH- ions.
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07:28pH at the Equivalence Point Example
Related Practice
Textbook Question
You have to prepare a pH = 5.00 buffer, and you have the following 0.10 M solutions available: HCOOH, HCOONa, CH3COOH, CH3COONa, HCN, and NaCN. How many milliliters of each solution would you use to make approximately 1 L of the buffer?
Textbook Question
The accompanying graph shows the titration curves for two monoprotic acids. (d) Estimate the pKa of the weak acid.
Textbook Question
Compare the titration of a strong, monoprotic acid with a strong base to the titration of a weak, monoprotic acid with a strong base. Assume the strong and weak acid solutions initially have the same concentrations. Indicate whether the following statements are true or false. (a) More base is required to reach the equivalence point for the strong acid than the weak acid.
Textbook Question
The samples of nitric and acetic acids shown here are both titrated with a 0.100 M solution of NaOH(aq).
Determine whether each of the following statements concerning these titrations is true or false. (a) A larger volume of NaOH1aq2 is needed to reach the equivalence point in the titration of HNO3.
Textbook Question
Determine whether each of the following statements concerning the titrations in Problem 17.35 is true or false. (a) The pH at the beginning of the two titrations will be the same.