You have to prepare a pH = 5.00 buffer, and you have the following 0.10 M solutions available: HCOOH, HCOONa, CH3COOH, CH3COONa, HCN, and NaCN. Which solutions would you use?

검증된 단계별 안내

insert step 1> Identify the pKa values of the acids available: HCOOH, CH3COOH, and HCN.

insert step 2> Compare the pKa values to the desired pH of the buffer, which is 5.00.

insert step 3> Choose the acid whose pKa is closest to the desired pH, as this will provide the most effective buffer.

insert step 4> Select the corresponding salt of the chosen acid to pair with it, forming the buffer system.

insert step 5> Use the Henderson-Hasselbalch equation to verify that the chosen acid and its conjugate base can achieve the desired pH.

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주요 개념

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Buffer Solutions

Buffer solutions are mixtures that resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. In this case, a buffer at pH 5.00 can be created using a weak acid and its salt, which helps maintain the desired pH level.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the concentration of the 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 is essential for determining the appropriate ratio of acid to base needed to achieve a specific pH.

pKa Values

The pKa value is a measure of the strength of an acid in solution, indicating the pH at which half of the acid is dissociated. For effective buffer preparation, it is important to choose a weak acid with a pKa close to the desired pH. In this scenario, knowing the pKa values of the available acids (HCOOH, CH3COOH, HCN) will help identify which acid-base pair can effectively create a buffer at pH 5.00.