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Ch.18 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Non è quello che usi tu?Cambia libro di testo
Capitolo 18, Problema 95b

Use the given molar solubilities in pure water to calculate Ksp for each compound. b. PbF2; molar solubility = 5.63⨉10-3 M c. MgF2; molar solubility = 2.65⨉10-4 M

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1
Identify the dissolution equation for the compound. For PbF2, the dissolution equation is: PbF2(s) ⇌ Pb2+(aq) + 2F-(aq).
Write the expression for the solubility product constant (Ksp) based on the dissolution equation. For PbF2, Ksp = [Pb2+][F-]^2.
Substitute the molar solubility into the Ksp expression. Given the molar solubility of PbF2 is 5.63⨉10-3 M, [Pb2+] = 5.63⨉10-3 M and [F-] = 2(5.63⨉10-3) M.
Calculate the concentration of F- by multiplying the molar solubility of PbF2 by 2, as there are two fluoride ions for every formula unit of PbF2 that dissolves.
Substitute these concentrations back into the Ksp expression and simplify to find the Ksp value for PbF2.

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Molar Solubility

Molar solubility is the number of moles of a solute that can dissolve in one liter of solution at a given temperature. It is a crucial measure in determining how much of a compound can be dissolved in water, which directly influences the calculation of the solubility product constant (Ksp). In this case, the molar solubility of PbF2 is given as 5.63 × 10^-3 M.
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Molar Solubility Example

Solubility Product Constant (Ksp)

The solubility product constant (Ksp) is an equilibrium constant that reflects the extent to which a sparingly soluble ionic compound dissolves in water. It is calculated from the concentrations of the ions in a saturated solution at equilibrium. For PbF2, Ksp can be derived from its dissociation into Pb²⁺ and F⁻ ions, using the molar solubility to express their concentrations.
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Solubility Product Constant

Dissociation of Ionic Compounds

Dissociation refers to the process by which an ionic compound separates into its constituent ions when dissolved in water. For PbF2, the dissociation can be represented as PbF2(s) ⇌ Pb²⁺(aq) + 2F⁻(aq). Understanding this process is essential for calculating Ksp, as it allows us to relate the molar solubility to the concentrations of the ions produced in solution.
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Ionic Compounds Naming