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Ch.17 - Applications of Aqueous Equilibria
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.17 - Applications of Aqueous EquilibriaProblem 41b
Chapter 17, Problem 41b

The following plot shows two pH titration curves, each representing the titration of 50.0 mL of 0.100 M acid with 0.100 M NaOH:
Graph showing pH titration curves for weak acids with NaOH, indicating equivalence points.
. (b) What is the approximate pH at the equivalence point for each of the acids?

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1
Identify the equivalence point on each titration curve. This is the point where the curve shows a steep rise in pH, indicating that the amount of NaOH added is stoichiometrically equivalent to the amount of acid present.
For each curve, locate the volume of NaOH added at the equivalence point. This is typically where the curve is the steepest.
Determine the pH at the equivalence point for each curve by reading the pH value corresponding to the volume of NaOH added at the equivalence point.
Compare the pH values at the equivalence points for the two acids. Note that the pH at the equivalence point for a weak acid titrated with a strong base is typically greater than 7.
Record the approximate pH values at the equivalence points for each of the acids based on the graph.

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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 an unknown solution by reacting it with a solution of known concentration. In this case, the titration involves a weak acid being neutralized by a strong base (NaOH), which results in a change in pH that can be plotted to visualize the reaction's progress.
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Acid-Base Titration

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 of the solution changes dramatically, often indicated by a steep slope in the titration curve.
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At the Equivalence Point

pH of the Equivalence Point

The pH at the equivalence point varies depending on the strength of the acid and base involved in the titration. For a weak acid titrated with a strong base, the pH at the equivalence point will be greater than 7 due to the formation of a weak conjugate base, which can hydrolyze in water, resulting in a basic solution.
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pH at the Equivalence Point Example
Related Practice
Textbook Question

The following pictures represent solutions at various stages in the titration of a weak base B with aqueous HCl. (Cl- ions and solvent water molecules have been omitted for clarity.)

. (b) Is the pH at the equivalence point more or less than 7?

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Textbook Question

The following pictures represent solutions that contain one or more of the compounds H2A, NaHA, and Na2A, where H2A is a weak diprotic acid. (Na+ ions and solvent water molecules have been omitted for clarity.)

(b) Which solution has the greatest buffer capacity?

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Textbook Question

The following pictures represent solutions that contain one or more of the compounds H2A, NaHA, and Na2A, where H2A is a weak diprotic acid. (Na+ ions and solvent water molecules have been omitted for clarity.)

(a) Which of the solutions are buffer solutions?

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Textbook Question
The following pictures represent solutions at various stages in the titration of a weak diprotic acid H2A with aqueous NaOH. (Na+ ions and water molecules have been omitted for clarity.)

.(b) Which solution has the highest pH? Which has the lowest pH?
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Textbook Question

The following pictures represent solutions at various stages in the titration of a weak base B with aqueous HCl. (Cl- ions and solvent water molecules have been omitted for clarity.)

. (a) To which of the following stages do solutions 1–4 correspond? (i) The initial solution before addition of any HCl (ii) Halfway to the equivalence point (iii) At the equivalence point (iv) Beyond the equivalence point

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Textbook Question

The following pictures represent initial concentrations in solutions that contain a weak acid HA (pKa = 6.0) and its sodium salt NaA. (Na+ ions and solvent water molecules have been omitted for clarity.)

. (b) Draw a picture that represents the equilibrium state of solution (1) after the addition of two H3O+ ions.

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