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Ch.16 - Aqueous Equilibria: Acids & Bases
Chapter 16, Problem 125

Write a balanced net ionic equation for the principal reaction in solutions of each of the following salts. In each case, identify the Brønsted–Lowry acids and bases and the conjugate acid–base pairs. (a) Na2CO3

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Identify the ions formed when Na2CO3 (sodium carbonate) dissolves in water. Na2CO3 dissociates into 2 Na+ (sodium ions) and CO3^2- (carbonate ions).
Determine the reaction of the carbonate ion (CO3^2-) with water. CO3^2- acts as a Brønsted–Lowry base because it can accept a proton (H+) from water, forming HCO3^- (bicarbonate ion) and OH^- (hydroxide ion).
Write the net ionic equation for the reaction of CO3^2- with water: CO3^2- (aq) + H2O (l) -> HCO3^- (aq) + OH^- (aq).
Identify the Brønsted–Lowry acid and base in the reaction. The base is CO3^2- as it accepts a proton, and the acid is H2O as it donates a proton.
Identify the conjugate acid-base pairs. The conjugate acid-base pair is CO3^2-/HCO3^- and H2O/OH^-.

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Key Concepts

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

Net Ionic Equations

A net ionic equation represents the chemical species that are involved in a reaction, excluding spectator ions. It focuses on the ions and molecules that undergo a change during the reaction, providing a clearer picture of the actual chemical process. To write a net ionic equation, one must first write the complete ionic equation and then remove the ions that do not participate in the reaction.
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Brønsted–Lowry Acids and Bases

The Brønsted–Lowry theory defines acids as proton donors and bases as proton acceptors. This concept emphasizes the transfer of protons (H⁺ ions) in chemical reactions, allowing for a broader understanding of acid-base behavior beyond just the presence of hydroxide or hydronium ions. Identifying acids and bases in a reaction helps in determining the conjugate acid-base pairs formed during the process.
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Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of two species that differ by the presence of a single proton. When an acid donates a proton, it becomes its conjugate base, while the base that accepts the proton becomes its conjugate acid. Understanding these pairs is crucial for analyzing acid-base reactions, as they illustrate the reversible nature of these processes and help predict the direction of equilibrium.
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