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Ch.17 - Aqueous Ionic Equilibrium
Chapter 17, Problem 85b

Write balanced equations and expressions for Ksp for the dissolution of each ionic compound. b. PbBr2

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Write the dissolution equation for PbBr<sub>2</sub>. When PbBr<sub>2</sub> dissolves in water, it dissociates into its constituent ions. The equation is: PbBr<sub>2</sub>(s) → Pb<sup>2+</sup>(aq) + 2 Br<sup>-</sup>(aq).
Ensure the equation is balanced. Check that the number of atoms for each element on the reactant side equals the number on the product side. In this case, 1 Pb atom and 2 Br atoms on both sides confirm the equation is balanced.
Write the expression for the solubility product constant (Ksp). Ksp expressions are derived from the equilibrium constant expression for the dissolution process, including only the products raised to the power of their stoichiometric coefficients.
Substitute the ions into the Ksp expression. For PbBr<sub>2</sub>, the expression is: Ksp = [Pb<sup>2+</sup>][Br<sup>-</sup>]^2.
Note that the coefficients in the balanced equation become the exponents in the Ksp expression, reflecting the stoichiometry of the dissolution process.

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Key Concepts

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

Solubility Product Constant (Ksp)

The solubility product constant (Ksp) is an equilibrium constant that quantifies the solubility of a sparingly soluble ionic compound. It is defined as the product of the molar concentrations of the ions, each raised to the power of their coefficients in the balanced dissolution equation. Ksp values are specific to temperature and provide insight into the extent to which a compound can dissolve in water.
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Dissolution of Ionic Compounds

The dissolution of ionic compounds involves the separation of the compound into its constituent ions when it is added to a solvent, typically water. For example, when lead(II) bromide (PbBr2) dissolves, it dissociates into lead ions (Pb²⁺) and bromide ions (Br⁻). This process is represented by a balanced chemical equation that reflects the stoichiometry of the ions produced.
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Balanced Chemical Equations

A balanced chemical equation represents a chemical reaction with equal numbers of each type of atom on both sides of the equation. Balancing is essential to comply with the law of conservation of mass. In the context of Ksp, the balanced equation for the dissolution of an ionic compound is crucial for accurately determining the Ksp expression, as it dictates the concentrations of the ions involved.
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