Lawrence Joseph Henderson introduced an equation in 1908 to calculate hydrogen concentration in buffer solutions. This derivation, later re-expressed in logarithmic form by Karl Albert Hasselbalch, remains a vital formula for determining the pH of buffer solutions.
A buffer solution comprises either:
Conjugate forms are often referred to as "salts." Buffer solutions are crucial in stabilizing pH for reaction kinetics and equilibrium processes.
Must Check - TCA cycle and Electron Transport System
| Equation | Description |
pH = pKa + log10([A-]/[HA]) | Used for acidic buffer solutions. |
pOH = pKb + log10([BH+]/[B]) | Used for basic buffer solutions. |
For Weak Acids:
HA: HA + H2O ⇋ H+ + A-Ka: Ka = [H+][A-]/[HA]-log Ka = -log ([H+][A-]/[HA])-log [H+] = pH and -log Ka = pKa: pH = pKa + log ([A-]/[HA])For Weak Bases:
B: B + H2O ⇋ OH- + BH+Kb: Kb = [BH+][OH-]/[B]-log Kb = -log ([BH+][OH-]/[B])-log [OH-] = pOH and -log Kb = pKb: pOH = pKb + log ([BH+]/[B])Also Check - Third Law of Thermodynamics
| Scenario | Implication |
pH = pKa | The acid is half dissociated, and [A-] = [HA]. |
| Change in pH | A tenfold change in [A-]/[HA] occurs for every unit change in the pH-pKa ratio. |
| Limitation | Reason |
| Fails for strong acids and bases | Assumes constant acid/base concentrations, neglecting proton binding and ionization effects. |
| Inaccurate for highly dilute solutions | Ignores the self-dissociation of water, affecting pH calculations. |
Key Takeaways
The Henderson-Hasselbalch equation is an essential tool for understanding pH balance in buffer solutions. Mastering its applications, derivation, and limitations ensures accurate results in scientific and academic pursuits.
For further learning, explore related topics like Heat Capacity and Specific Heat.
The pH of a solution is a measurement of the total number of H+ ions in the solution. This word is also useful in determining the acidity of a solution.
When we add any acidic or basic component to a buffer solution, the pH does not change and it resists. Buffers include acidic components, such as HA, that neutralize OH- ions, as well as basic components, such as A-, that neutralize H+ ions. It will always maintain the pH of the solution by neutralizing little amounts of acid or base.
When estimating the pH levels in a buffer solution, this equation is crucial. In terms of pharmaceutical analysis, this mostly aids in the calculation of a molecule's PKA value using a chemical moiety. It's also useful for estimating the ratio of its ionized and unionized versions. This does, however, cover certain additional processes that are involved.