Using values of Ka in Appendix C, calculate values of Kb for each of the following ions. (a) Fluoride ion, F-

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Identify the conjugate acid of the fluoride ion, F-. The conjugate acid of F- is HF (hydrofluoric acid).

Look up the acid dissociation constant (Ka) for HF in Appendix C of your textbook or a reliable chemistry resource.

Use the relationship between the acid dissociation constant (Ka) for the conjugate acid and the base dissociation constant (Kb) for the conjugate base. The relationship is given by the equation: Kb = Kw / Ka, where Kw is the ion-product constant of water at 25°C (approximately 1.0 x 10^-14).

Substitute the Ka value of HF into the equation to calculate Kb for the fluoride ion, F-.

Ensure all units are consistent and calculate Kb using appropriate scientific notation to express the small values typically found in dissociation constants.

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Key Concepts

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

Acid-Base Equilibrium

Acid-base equilibrium refers to the balance between acids and bases in a solution, characterized by the dissociation of acids into protons (H+) and their conjugate bases. The strength of an acid is quantified by its acid dissociation constant (Ka), while the strength of a base is measured by its base dissociation constant (Kb). Understanding this equilibrium is essential for calculating Kb from Ka values.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of an acid and its corresponding base that differ by a single proton. For example, when fluoride ion (F-) acts as a base, it can accept a proton to form its conjugate acid, HF. The relationship between Ka and Kb for a conjugate pair is given by the equation: Ka × Kb = Kw, where Kw is the ion product of water (1.0 x 10^-14 at 25°C).

Calculating Kb from Ka

To calculate Kb from Ka, one can use the relationship between the two constants and the ion product of water. Specifically, Kb can be determined using the formula Kb = Kw / Ka. This calculation is crucial for determining the basicity of ions like fluoride, allowing for a deeper understanding of their behavior in aqueous solutions.

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Ka and Kb Relationship

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