Calculate the pH of the buffers in problem 19 after adding 5.0 ×10^-4 mol of HCl.

Name: Problem 20, Chapter 6: Modern analytical chemistry
Uploaded: 2020-09-13T01:45:10-08:00
Duration: 5 min 6 s
Channel: Susan Hallstrom
Description: Calculate the pH of the buffers in problem 19 after adding 5.0 ×10^-4 mol of HCl.

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Calculate the pH of the buffers in problem 19 after adding...

Key Concepts

pH Calculation

Calculating the pH of a buffer, particularly after the addition of an acid or base, involves determining the new concentrations of the buffer components after the neutralization reaction has occurred, and then applying equilibrium concepts or the Henderson–Hasselbalch equation to find the resulting pH. This process emphasizes the interplay between the acid dissociation equilibrium and stoichiometric adjustments in buffer composition.

Acid-Base Neutralization in Buffers

In buffer systems, the addition of a strong acid leads to a neutralization reaction where the conjugate base reacts with the added hydrogen ions to form more of the weak acid, thus minimizing drastic changes in pH. The effectiveness of this neutralization depends on the proportions of the weak acid and conjugate base present in the buffer.

Buffer Solutions

A buffer solution consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) and is used to resist changes in pH upon the addition of small amounts of strong acid or base. The unique ability of a buffer to maintain a relatively constant pH stems from the equilibrium between the weak acid and its conjugate base, which adjusts to neutralize added hydrogen or hydroxide ions.

Henderson–Hasselbalch Equation

The Henderson–Hasselbalch equation provides a simplified means of calculating the pH of a buffer solution by relating the pH to the pKa of the weak acid and the ratio of the concentrations of the conjugate base to the acid. This equation is useful for calculating the shift in pH when a known quantity of strong acid or base is added to the buffer.

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