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Ch.18 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.18 - Aqueous Ionic EquilibriumProblem 75
Chapter 18, Problem 75

Consider the titration of a 25.0-mL sample of 0.115 M RbOH with 0.100 M HCl. Determine each quantity. a. the initial pH d. the pH at the equivalence point e. the pH after adding 5.0 mL of acid beyond the equivalence point

Verified step by step guidance
1
Step 1: Calculate the initial pH of the RbOH solution. Since RbOH is a strong base, it dissociates completely in water. Use the concentration of RbOH to find the hydroxide ion concentration, [OH^-], and then calculate the pOH. Finally, convert pOH to pH using the relation pH + pOH = 14.
Step 2: Determine the volume of HCl needed to reach the equivalence point. At the equivalence point, the moles of HCl added will equal the moles of RbOH initially present. Use the initial concentration and volume of RbOH to find the moles of RbOH, and then use the concentration of HCl to find the volume of HCl required.
Step 3: Calculate the pH at the equivalence point. At the equivalence point, the solution contains only water and the salt RbCl, which does not affect the pH. Therefore, the pH is neutral, which is 7.0 at 25°C.
Step 4: Calculate the moles of HCl added beyond the equivalence point. Use the additional volume of HCl added (5.0 mL) and its concentration to find the moles of excess HCl.
Step 5: Determine the pH after adding 5.0 mL of acid beyond the equivalence point. The excess HCl will determine the pH. Calculate the concentration of H^+ ions from the excess HCl in the total volume of the solution, and then find the pH using the formula pH = -\(\log\)[H^+].

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Titration

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 (a solution of known concentration) to a sample solution until the reaction reaches its equivalence point, where the amount of titrant equals the amount of substance in the sample. Understanding the titration process is essential for calculating pH changes during the addition of acid or base.
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03:04
Acid-Base Titration

pH and pH Scale

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. The pH scale ranges from 0 to 14, with values below 7 indicating acidic solutions, 7 being neutral, and above 7 indicating basic solutions. Knowing how to calculate pH at different stages of a titration, including before, at, and after the equivalence point, is crucial for solving the given problem.
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The pH Scale

Equivalence Point

The equivalence point in a titration is the stage at which the amount of titrant added is stoichiometrically equivalent to the amount of substance present in the sample solution. At this point, the reaction between the acid and base is complete, and the pH can change dramatically depending on the nature of the acid and base involved. Understanding the characteristics of the equivalence point helps in predicting the pH and determining the final concentrations of the resulting solution.
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Related Practice
Textbook Question

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Textbook Question

Consider the titration of a 35.0-mL sample of 0.175 M HBr with 0.200 M KOH. Determine each quantity. e. the pH after adding 5.0 mL of base beyond the equivalence point

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Textbook Question

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Textbook Question

Consider the titration of a 35.0-mL sample of 0.175 M HBr with 0.200 M KOH. Determine each quantity. b. the volume of added base required to reach the equivalence point

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Textbook Question

Consider the titration of a 25.0-mL sample of 0.115 M RbOH with 0.100 M HCl. Determine each quantity. b. the volume of added acid required to reach the equivalence point

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