Henderson Hasselbalch Equation

The Henderson-Hasselbalch equation is a chemical and biological equation for determining the pH of the solution. As far as the pH of solutions, pKa  / pKb, and the concentrations of reactive species are concerned, they are all represented by this equation(pH = pKa  + log10  ([A–]/[HA])). To measure the pH of the bicarbonate buffer system within the blood, American biologist L. J. Henderson, and the Swedish physiologist K. A. Hasselbalch, separately derived this equation. 

For over a century, this form of kinetic analysis has allowed us to theoretically connect variations inside the acidic strength of dilute solutions towards the amount of acid and base supplied or withdrawn.

This equation is utilised to calculate the quantity of acid and the conjugate base needed to make a pH-neutral buffer.

Objectives

The following points explain the importance of the Henderson Hasselbalch equation. Take a look:

• Depending on the initial proportion of the acid, the Henderson Hasselbalch equation helps determine the pH, pOH, [H3O+]tot, [OH-]tot, [H3O+]water, & [OH-]water in a solution that contains a strong acid (base).

• The Henderson Hasselbalch equation explains that a buffer solution (whether acidic or basic) may withstand considerable pH changes if a modest quantity of acid or base is introduced.

• The equation describes how to make both an acidic and basic buffer solution.

• It explains what a “buffer solution” is.

• It defines the term “buffer capacity.”

• Given the value of Ka  & Kb of conjugate acid-base pairings, the equation can be used to calculate if an aqueous solution containing salt would be acidic, basic, or neutral.

• It explains how well the relative strengths between conjugate acids or bases may be determined utilising Kb and Ka numbers for bases & acids, correspondingly.

• The Henderson Hasselbalch equation identifies the protonation status of several biomolecule functional groups.

Equation

The method to represent the Henderson Hasselbalch equation:

pH = pKa  + log10  ([A–]/[HA])

where pKa= dissociation constant of acid

Applications of Henderson Hasselbalch Equation

Using pKa to calculate the pH of a solution

This formula can calculate the pH of various solutions in chemical equations and biological systems such as cellular proteins. Similarly,

pOH=pKb+log([salt]/[base])

Chemical ionised and unionised concentrations are calculated.

The capacity to determine the amounts of ionised and unionised compounds is one of the most potent uses of the Henderson Hasselbalch equation. Spectroscopic techniques measure the quantity of ionised and unionised species. Hence, this equation is beneficial when spectroscopic investigations are not possible. Knowing the concentration of ionised and unionised substances is crucial in organic chemistry, analytical chemistry, or medicinal sciences. 

Using pH to calculate pKa of a solution

Whenever the ratio of ionised and unionised molecules and the solution pH are given, the Henderson Hasselbalch equation can calculate the pKa.

Solubility determination

The Henderson Hasselbalch equation can estimate the pH dependence of solubility. The solubility of a solution may be calculated based on its pH, and there is a strong link between pH and the solubility of different components in a solution.

Calculating a protein’s isoelectric point

This formula may also be used to figure out a protein’s isoelectric point.

Limitations

• The most important implication in this equation is that the equilibrium, both acid concentration and its conjugate base, would remain constant.

• The importance of water hydrolysis and its impact upon the pH of the entire solution is often overlooked.

• Likewise, the hydrolysis of base & acid dissociation is not considered.

• When dealing with strong acids or bases, the assertion made inside the equation may fail.

Conclusion

Because the Henderson Hasselbalch equation’s importance is to teach acid-base equilibrium, it gets more attention in general, quantitative, & biochemistry classes. The equation can analyse titration curves, buffer difficulties, and various other related concepts. Lawrence Henderson was the first to devise a formula for calculating the pH of a buffer solution in 1908, and as a result, Henderson’s equation was widely used. Karl Hasselbalch revised the formula in 1917 to convert it to exponential values. The Henderson Hasselbalch formula was born as a result of this process.