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Ch.17 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831Non è quello che usi tu?Cambia libro di testo
Capitolo 17, Problema 91

Two compounds with general formulas AX and AX2 have Ksp = 1.5⨉10-5. Which of the two compounds has the higher molar solubility?

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1
Identify the dissociation reactions for both compounds. For AX, the reaction can be written as AX(s) ⇌ A+(aq) + X-(aq). For AX2, the reaction can be written as AX2(s) ⇌ A+(aq) + 2X2-(aq).
Write the expression for the solubility product constant (Ksp) for each compound. For AX, Ksp = [A+][X-]. For AX2, Ksp = [A+][2X-]^2.
Assume the molar solubility of AX is 's' mol/L, then [A+] = s and [X-] = s. Substitute these into the Ksp expression for AX to get Ksp = s^2.
Assume the molar solubility of AX2 is 's' mol/L, then [A+] = s and [2X-] = 2s. Substitute these into the Ksp expression for AX2 to get Ksp = s(2s)^2 = 4s^3.
Compare the expressions derived for Ksp in terms of 's' for both compounds. The compound with the simpler expression (AX) will generally have a higher molar solubility than the compound with the more complex expression (AX2) when Ksp values are the same.

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Concetti chiave

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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 equation. A higher Ksp value indicates greater solubility of the compound in solution.
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Solubility Product Constant

Molar Solubility

Molar solubility refers to the maximum amount of a solute that can dissolve in a given volume of solvent at equilibrium, expressed in moles per liter (mol/L). It is directly related to Ksp, as the molar solubility can be calculated from the Ksp value for a given compound, allowing for comparison between different compounds.
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Molar Solubility Example

Comparative Solubility of Compounds

When comparing the solubility of compounds with different stoichiometries, such as AX and AX2, it is essential to consider how the dissociation of each compound affects the concentration of ions in solution. For example, AX dissociates into one ion, while AX2 dissociates into two, which influences the Ksp expression and ultimately the molar solubility of each compound.
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Solubility Rules