Skip to main content
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 95d
Chapter 17, Problem 95d

Consider the titration of 50.0 mL of a 0.100 M solution of the protonated form of the amino acid alanine (H2A+: Ka1 = 4.6 × 10–3, Ka2 = 2.0 × 10–10) with 0.100 M NaOH. Calculate the pH after the addition of each of the following volumes of base. (d) 75.0 mL

Verified step by step guidance
1
Determine the initial moles of the protonated form of alanine (H2A+) using the initial concentration and volume: \( \text{moles of } H_2A^+ = 0.100 \text{ M} \times 0.050 \text{ L} \).
Calculate the moles of NaOH added using its concentration and the volume added: \( \text{moles of NaOH} = 0.100 \text{ M} \times 0.075 \text{ L} \).
Determine the limiting reactant by comparing the initial moles of H2A+ and the moles of NaOH added.
Identify the species present after the reaction and their concentrations. If NaOH is in excess, calculate the concentration of OH- ions.
Use the concentration of OH- ions to calculate the pOH, and then find the pH using the relation \( \text{pH} = 14 - \text{pOH} \).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
8m
Was this helpful?

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 (in this case, NaOH) to a solution containing the analyte (the protonated form of alanine) until the reaction reaches its equivalence point. The pH changes during this process can be monitored to understand the acid-base behavior of the solution.
Recommended video:
Guided course
03:04
Acid-Base Titration

Acid-Base Equilibria

Acid-base equilibria describe the balance between protonated and deprotonated forms of a substance in solution. For alanine, the two dissociation constants (Ka1 and Ka2) indicate how readily it donates protons. Understanding these constants is crucial for calculating the pH at various stages of the titration, especially when determining the pH after adding specific volumes of NaOH.
Recommended video:
Guided course
02:00
Arrhenius Acids and Bases

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation provides a way to calculate the pH of a buffer solution based on the concentrations of the acid and its conjugate base. It is expressed as pH = pKa + log([A-]/[HA]). This equation is particularly useful in titration scenarios, as it allows for the determination of pH at points where the solution contains both the protonated and deprotonated forms of the amino acid.
Recommended video:
Guided course
02:40
Henderson-Hasselbalch Equation
Related Practice
Textbook Question

Consider the titration of 50.0 mL of a 0.100 M solution of the protonated form of the amino acid alanine (H2A+: Ka1 = 4.6 × 10–3, Ka2 = 2.0 × 10–10) with 0.100 M NaOH. Calculate the pH after the addition of each of the following volumes of base. (e) 100.0 mL

486
views
Textbook Question

Consider the titration of 50.0 mL of a 0.100 M solution of the protonated form of the amino acid alanine (H2A+: Ka1 = 4.6 × 10–3, Ka2 = 2.0 × 10–10) with 0.100 M NaOH. Calculate the pH after the addition of each of the following volumes of base. (a) 10.0 mL

889
views
Textbook Question
What is the pH at the equivalence point for the titration of 0.20 M solutions of the following acids and bases? Which of the indicators in Figure 17.5 would be suitable for each titration? (c) Ba(OH)2 and HBr

380
views
Textbook Question

Consider the titration of 50.0 mL of a 0.100 M solution of the protonated form of the amino acid alanine (H2A+: Ka1 = 4.6 × 10–3, Ka2 = 2.0 × 10–10) with 0.100 M NaOH. Calculate the pH after the addition of each of the following volumes of base. (b) 25.0 mL (c) 50.0 mL

Textbook Question
The titration of 0.02500 L of a diprotic acid solution with 0.1000 M NaOH requires 34.72 mL of titrant to reach the second equivalence point. The pH is 3.95 at the first equiva-lence point and 9.27 at the second equivalence point. If the acid solution contained 0.2015 g of the acid, what is the molar mass, pKa1, and pKa2 of the acid?
853
views
Textbook Question

Consider the titration of 50.0 mL of 1.00 M H3PO4 with 1.00 M KOH. Calculate the pH after the addition of each of the following volumes of base. (a) 25.0 mL (c) 75.0 mL

286
views