Solve an equilibrium problem (using an ICE table) to calculate the pH of each solution. c. a mixture that is 0.15 M in HF and 0.15 M in NaF

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Identify the components of the solution: HF is a weak acid and NaF is its conjugate base, making this a buffer solution.

Write the equilibrium expression for the dissociation of HF: \( \text{HF} \rightleftharpoons \text{H}^+ + \text{F}^- \).

Set up an ICE table (Initial, Change, Equilibrium) to determine the concentrations of each species at equilibrium. Initially, [HF] = 0.15 M and [F^-] = 0.15 M, with [H^+] = 0.

Use the expression for the acid dissociation constant \( K_a \) of HF: \( K_a = \frac{[\text{H}^+][\text{F}^-]}{[\text{HF}]} \). Substitute the equilibrium concentrations from the ICE table into this expression.

Solve for \([\text{H}^+]\) using the \( K_a \) value for HF, and then calculate the pH using the formula \( \text{pH} = -\log[\text{H}^+] \).

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주요 개념

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Weak Acids and Conjugate Bases

HF (hydrofluoric acid) is a weak acid that partially dissociates in solution, while NaF (sodium fluoride) provides the conjugate base F-. The presence of both a weak acid and its conjugate base in a solution creates a buffer system, which helps maintain a relatively stable pH when small amounts of acid or base are added.

ICE Table (Initial, Change, Equilibrium)

An ICE table is a tool used to organize the initial concentrations, the changes in concentrations as the reaction reaches equilibrium, and the final equilibrium concentrations. For the equilibrium problem involving HF and F-, the ICE table will help calculate the concentrations of H+ ions, which are necessary for determining the pH of the solution.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the concentration of the weak acid and its conjugate base. It is expressed as pH = pKa + log([A-]/[HA]), where pKa is the negative logarithm of the acid dissociation constant. This equation simplifies the calculation of pH in buffer solutions like the one formed by HF and NaF.