Buffer Solutions Calculations to Know for General Chemistry II

Buffer solutions are essential in chemistry for maintaining stable pH levels. Understanding the Henderson-Hasselbalch equation and buffer capacity calculations helps predict how buffers react to added acids or bases, ensuring effective pH control in various applications.

1. Henderson-Hasselbalch equation

   • The equation is expressed as: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid.
   • It provides a quick way to estimate the pH of a buffer solution based on the concentrations of the acid and its conjugate base.
   • The equation is derived from the acid dissociation constant (Ka) and is applicable to weak acid/conjugate base pairs.

2. Buffer capacity calculation

   • Buffer capacity is the ability of a buffer solution to resist changes in pH upon the addition of acids or bases.
   • It is calculated using the formula: β = ΔB/ΔpH, where ΔB is the amount of strong acid or base added, and ΔpH is the resulting change in pH.
   • A higher concentration of the buffer components results in greater buffer capacity.

3. pH calculation of a buffer solution

   • The pH of a buffer can be calculated using the Henderson-Hasselbalch equation.
   • It is essential to know the concentrations of both the weak acid and its conjugate base to determine the pH accurately.
   • The pH of a buffer remains relatively stable compared to non-buffered solutions when acids or bases are added.

4. pKa and Ka relationship

   • pKa is the negative logarithm of the acid dissociation constant (Ka): pKa = -log(Ka).
   • A lower pKa value indicates a stronger acid, while a higher pKa indicates a weaker acid.
   • The pKa value is crucial for determining the pH of a buffer solution using the Henderson-Hasselbalch equation.

5. Calculating the ratio of acid to conjugate base

   • The ratio [A-]/[HA] can be derived from the Henderson-Hasselbalch equation to find the desired pH.
   • This ratio helps in preparing buffer solutions with specific pH values.
   • It is important to maintain the correct ratio to ensure the buffer's effectiveness.

6. Determining buffer range

   • The buffer range is the pH range over which a buffer solution can effectively maintain its pH.
   • Typically, the effective buffer range is within ±1 pH unit of the pKa of the weak acid.
   • Knowing the buffer range is essential for selecting appropriate buffers for specific applications.

7. Preparing a buffer with a specific pH

   • To prepare a buffer, mix a weak acid with its conjugate base in the correct ratio as determined by the Henderson-Hasselbalch equation.
   • Adjust the concentrations of the acid and base to achieve the desired pH.
   • Use a pH meter to verify the pH after preparation and make adjustments if necessary.

8. Effect of dilution on buffer pH

   • Diluting a buffer solution generally does not significantly change its pH, as both the acid and conjugate base are diluted equally.
   • However, extreme dilution can lead to a decrease in buffer capacity and may affect pH stability.
   • It is important to consider the concentrations of buffer components when diluting.

9. Buffer action against added acid or base

   • Buffers work by neutralizing added acids or bases, minimizing pH changes.
   • When a strong acid is added, the conjugate base reacts with it, while the weak acid can react with added strong base.
   • The effectiveness of a buffer depends on its capacity and the concentrations of its components.

10. Calculating the change in pH upon addition of strong acid or base

    • The change in pH can be estimated using the buffer capacity formula: ΔpH = ΔB/(β).
    • It is important to know the initial pH and the amount of strong acid or base added to calculate the new pH.
    • This calculation helps predict how a buffer will respond to perturbations in pH.