Textbook Question
In which of these solutions will HNO2 ionize less than it does in pure water? a. 0.10 M NaCl b. 0.10 M KNO3 c. 0.10 M NaOH d. 0.10 M NaNO2
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Ch.17 - Aqueous Ionic Equilibrium
Chapter 17, Problem 29a
Solve an equilibrium problem (using an ICE table) to calculate the pH of each solution. a. a solution that is 0.20 M in HCHO2 and 0.15 M in NaCHO2
Verified step by step guidance1
Start by identifying the weak acid and its conjugate base in the solution. Here, HCHO2 (formic acid) is the weak acid, and NaCHO2 provides the conjugate base, CHO2^-.
Write the equilibrium expression for the dissociation of the weak acid: HCHO2 \rightleftharpoons H^+ + CHO2^-.
Set up an ICE table (Initial, Change, Equilibrium) to track the concentrations of each species. Initially, [HCHO2] = 0.20 M, [CHO2^-] = 0.15 M, and [H^+] = 0.
Define the change in concentration using a variable, x, where x is the amount of HCHO2 that dissociates: [HCHO2] = 0.20 - x, [CHO2^-] = 0.15 + x, [H^+] = x.
Use the acid dissociation constant (Ka) for formic acid to set up the equation: Ka = \frac{x(0.15 + x)}{0.20 - x}. Solve for x to find [H^+], then calculate pH using pH = -\log[H^+].
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Equilibrium
Acid-base equilibrium refers to the state where the concentrations of acids and their conjugate bases in a solution remain constant over time. In this context, the weak acid HCHO2 (formic acid) and its conjugate base NaCHO2 (sodium formate) establish an equilibrium that can be analyzed using the Henderson-Hasselbalch equation or an ICE table to determine the pH of the solution.
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ICE Table
An ICE table (Initial, Change, Equilibrium) is a tool used to organize the concentrations of reactants and products in a chemical reaction at different stages. For equilibrium problems, it helps to track the initial concentrations, the changes that occur as the system reaches equilibrium, and the final concentrations, which are essential for calculating pH in acid-base reactions.
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Henderson-Hasselbalch Equation
The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid. This equation is particularly useful for solutions containing both a weak acid and its conjugate base, allowing for quick pH estimations.
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Related Practice
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Textbook Question
Calculate the percent ionization of a 0.15 M benzoic acid solution in pure water and in a solution containing 0.10 M sodium benzoate. Why does the percent ionization differ significantly in the two solutions?