Ch.4 - Reactions in Aqueous Solution

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 95

Chapter 4, Problem 95

Why do we use a double arrow to show the dissociation of a weak acid or weak base in aqueous solution?

Verified step by step guidance

Understand that a double arrow in chemical equations (⇌) indicates a reversible reaction, where the reactants form products and the products can also revert back to reactants.

Recognize that weak acids and weak bases do not completely dissociate in water. Instead, they partially dissociate, establishing an equilibrium between the undissociated and dissociated forms.

Identify that the double arrow signifies this equilibrium state, showing that both the forward reaction (dissociation of the weak acid or base) and the reverse reaction (re-association of the ions into the weak acid or base) are occurring simultaneously.

Realize that the position of the equilibrium (how far the reaction proceeds in the forward or reverse direction) is determined by the acid or base's dissociation constant (Ka or Kb), which quantifies the strength of the acid or base.

Apply this understanding to predict the behavior of weak acids and bases in solution, such as predicting pH or the concentrations of various ions at equilibrium.

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Key Concepts

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

Equilibrium in Chemical Reactions

In chemical reactions, especially those involving weak acids and bases, equilibrium refers to the state where the forward and reverse reactions occur at the same rate. This means that the concentrations of reactants and products remain constant over time. The double arrow indicates that both the dissociation and recombination processes are happening simultaneously, reflecting the dynamic nature of the reaction.

Weak Acids and Bases

Weak acids and bases are substances that do not completely dissociate in solution. Unlike strong acids and bases, which fully ionize, weak acids and bases establish an equilibrium between the undissociated and dissociated forms. This incomplete dissociation is why we use a double arrow, as it signifies that the reaction can proceed in both directions.

Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is disturbed, the system will adjust to counteract the disturbance and restore a new equilibrium. In the context of weak acids and bases, changes in concentration, temperature, or pressure can shift the position of equilibrium, affecting the extent of dissociation. This principle helps explain the behavior of weak acids and bases in solution.

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Le Chatelier's Principle

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