Ch.18 - Aqueous Ionic Equilibrium

Tro - Chemistry: A Molecular Approach 5th Edition

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Tro 5th Edition

Ch.18 - Aqueous Ionic Equilibrium

Problem 27

Chapter 18, Problem 27

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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Identify the common ion effect, which states that the ionization of a weak acid or base is suppressed in the presence of a common ion from another source.

Examine each option to determine if it contains a common ion with HNO2. HNO2 is a weak acid that partially dissociates into H+ and NO2- ions in solution.

Recognize that NaCl dissociates into Na+ and Cl- ions, neither of which is a common ion with HNO2, so it does not affect the ionization of HNO2.

Note that KNO3 dissociates into K+ and NO3- ions. Since NO3- is not the same as NO2-, it does not provide a common ion to HNO2, thus not affecting its ionization.

Identify that NaNO2 dissociates into Na+ and NO2- ions. The NO2- ion is a common ion with HNO2, which will suppress the ionization of HNO2 due to the common ion effect.

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Key Concepts

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

Ionization of Weak Acids

Weak acids, like HNO2 (nitrous acid), do not fully ionize in solution. The degree of ionization depends on the concentration of the acid and the presence of other ions in the solution. In pure water, HNO2 will ionize to a certain extent, but this ionization can be affected by the addition of other solutes.

Common Ion Effect

The common ion effect occurs when a salt containing an ion that is also produced by the weak acid is added to the solution. This increases the concentration of that ion, shifting the equilibrium of the weak acid's ionization reaction to the left, thereby reducing the degree of ionization. For example, adding NaNO2 introduces NO2- ions, which will suppress the ionization of HNO2.

Colligative Properties

Colligative properties depend on the number of solute particles in a solution rather than their identity. When a non-volatile solute like NaCl or KNO3 is added to water, it can affect the physical properties of the solution, such as vapor pressure and boiling point. However, in the context of weak acid ionization, the presence of ions from strong electrolytes can influence the ionization behavior of weak acids.

Related Practice

Textbook Question

A formic acid solution has a pH of 3.25. Which of these substances will raise the pH of the solution upon addition? Explain your answer. a. HCl b. NaBr c. NaCHO₂ d. KCl

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?

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Textbook Question

Solve an equilibrium problem (using an ICE table) to calculate the pH of each solution. b. a solution that is 0.16 M in NH₃ and 0.22 M in NH₄Cl

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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

Verified video answer for a similar problem:

Key Concepts

Ionization of Weak Acids

Common Ion Effect

Colligative Properties

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