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Ch.17 - Applications of Aqueous Equilibria
All textbooksMcMurry 8th EditionCh.17 - Applications of Aqueous EquilibriaProblem 147
Chapter 17, Problem 147

Ethylenediamine (NH2CH2CH2NH2, abbreviated en) is an organic base that can accept two protons: (a) Consider the titration of 30.0 mL of 0.100 M ethylenediamine with 0.100 M HCl. Calculate the pH after the addition of the following volumes of acid, and construct a qualitative plot of pH versus milliliters of HCl added: (i) 0.0 mL (ii) 15.0 mL (iii) 30.0 mL (iv) 45.0 mL (v) 60.0 mL (vi) 75.0 mL

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Start by understanding that ethylenediamine (en) is a diprotic base, meaning it can accept two protons. The titration involves adding HCl, a strong acid, to the base solution.
Calculate the initial moles of ethylenediamine in the solution using the formula: moles = concentration (M) x volume (L).
For each volume of HCl added, calculate the moles of HCl using the same formula: moles = concentration (M) x volume (L).
Determine the reaction progress at each stage: (i) Before any HCl is added, (ii) After 15.0 mL of HCl is added, (iii) After 30.0 mL of HCl is added, (iv) After 45.0 mL of HCl is added, (v) After 60.0 mL of HCl is added, and (vi) After 75.0 mL of HCl is added. Consider the stoichiometry of the reaction where each mole of en can react with two moles of HCl.
For each stage, calculate the pH: (i) Initially, calculate the pH of the base solution using the Kb of ethylenediamine. (ii) At each subsequent stage, determine the pH by considering the remaining base, the formation of the conjugate acid, and the excess HCl, if any. Use the Henderson-Hasselbalch equation where applicable.>

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Key Concepts

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

Acid-Base Titration

An acid-base titration is a quantitative analytical method used to determine the concentration of an acid or base in a solution. In this process, a solution of known concentration (the titrant) is gradually added to a solution of unknown concentration until the reaction reaches its equivalence point, where the amount of acid equals the amount of base. The pH changes during the titration, which can be monitored to determine the endpoint.
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Buffer Solutions

Buffer solutions are mixtures that can resist changes in pH upon the addition of small amounts of acid or base. Ethylenediamine, being a weak base, can form a buffer system with its conjugate acid when protons are added. Understanding how buffers work is crucial for predicting pH changes during the titration of ethylenediamine with HCl, especially before and after the equivalence point.
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pH Calculation

pH is a measure of the acidity or basicity of a solution, calculated as the negative logarithm of the hydrogen ion concentration. In titrations, pH can be calculated at various points by considering the concentrations of the acid and base present, as well as the dissociation constants of the weak acid and base involved. This calculation is essential for constructing the pH versus volume plot during the titration of ethylenediamine with HCl.
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Related Practice
Textbook Question
A 0.0100 mol sample of solid Cd(OH)2 (Ksp = 5.3 x 10^-15) in 100.0 mL of water is titrated with 0.100 M HNO3. (c) How many milliliters of 0.100 M HNO3 must be added to completely neutralize the Cd(OH)2?
Textbook Question

A 40.0 mL sample of a mixture of HCl and H3PO4 was titrated with 0.100 M NaOH. The first equivalence point was reached after 88.0 mL of base, and the second equivalence point was reached after 126.4 mL of base. (a) What is the concentration of H3O+ at the first equivalence point?

Textbook Question

A 40.0 mL sample of a mixture of HCl and H3PO4 was titrated with 0.100 M NaOH. The first equivalence point was reached after 88.0 mL of base, and the second equivalence point was reached after 126.4 mL of base. (b) What are the initial concentrations of HCl and H3PO4 in the mixture?