Calculate Ph 0.136 M Hc5h9o2 and 0.136 M Nac5h9o2

Introduction

Calculating the pH of weak acid and conjugate base solutions is essential in chemistry and biochemistry. The pH of a solution containing a weak acid (HC5H9O2) and its conjugate base (NaC5H9O2) can be determined using the Henderson-Hasselbalch equation.

This calculation is particularly useful in buffer solutions, where the pH remains relatively stable when small amounts of acid or base are added. Understanding these calculations helps in designing effective buffers for various applications.

Formula

The Henderson-Hasselbalch equation is used to calculate the pH of a buffer solution:

For this calculation, we'll use the pKa value for HC5H9O2. The pKa value is a measure of the acid's strength and is specific to each acid.

Calculation

To calculate the pH of a solution containing 0.136 M HC5H9O2 and 0.136 M NaC5H9O2, follow these steps:

1. Identify the pKa value for HC5H9O2. For this example, we'll use pKa = 4.76.
2. Determine the concentrations of the weak acid (HC5H9O2) and its conjugate base (NaC5H9O2). Both are 0.136 M in this case.
3. Plug the values into the Henderson-Hasselbalch equation:

   pH = 4.76 + log₁₀([NaC5H9O2]/[HC5H9O2])

4. Calculate the ratio of the conjugate base to the weak acid:

   [NaC5H9O2]/[HC5H9O2] = 0.136 M / 0.136 M = 1

5. Calculate the logarithm of the ratio:

   log₁₀(1) = 0

6. Add the pKa value to the logarithm result:

   pH = 4.76 + 0 = 4.76

The calculated pH of the solution is 4.76.

Interpretation

A pH of 4.76 indicates that the solution is slightly acidic. This is expected since the pKa of HC5H9O2 is 4.76, which means the acid is partially dissociated at this pH.

When the concentrations of the weak acid and its conjugate base are equal, the pH equals the pKa. This is a characteristic of buffer solutions, where the pH remains stable when small amounts of acid or base are added.