The Importance of The Henderson-Hasselbalch Equation

Introduction 

The Henderson Hasselbalch formula formalises this concept, with A denoting the percentage of base ions (OH) and HA denoting the concentration of acid ions (H+).

The Henderson-Hasselbach equation is a formula that connects the pH of an acid’s aqueous solution to the acid’s acid dissociation constant.

pH=pkA+log10 [conjugate base]/[weak acid]

Whenever the percentages of the acid and conjugate base are equal, i.e. whenever the acidity is 50% dissociated, the pH of the solution equals the pKa of the acid, according to the Henderson-Hasselbach equation.

That is, when  [HA]=[A−]

The Henderson Hasselbalch formula approximates the link between a solution’s pH or pOH, its pKa or pKb, and the ratio of dissociated chemical species concentrations. The acid dissociation factor must be known before the equation could be used.

Equation

There are many ways to write the equation. Two of the most common ones are:

pH = pKa + log ([conjugate base]/[weak acid])

pOH = pKa + log ([conjugate acid]/[weak base])

In 1908, Lawrence Joseph Henderson devised a formula for calculating overall pH of a buffer solution. This formula was rewritten into logarithmic terms around 1917 by Karl Albert Hasselbalch.

Limitations

• The most important assumption within that equation is that during the equilibrium, the concentrations of acid as well as its conjugate base would stay unchanged.

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

• Hydrolysis of a base and acid dissociation are also ignored.

• When working with strong acids and bases, the assertion made with in equation may fail.

Importance of the Henderson-Hasselbalch equation

1. If indeed the initial concentrations of the weak acid and salt are known, the pH of a buffer solution can be computed.

For a basic buffer, however, the Henderson-Hasselbalch equation yields pOH, and the pH can be determined as (14 – pOH).

2. The pH of a buffer solution containing equimolar amounts of the acid (or base) and salt can be used to calculate the dissociation constant of a weak acid (or weak base).

Because [salt] equals [acid], log ([salt]/[acid]) = log 1 = 0.

pH (pKa) is a measurement of the acidity of a substance.

As a result, the pKa of the weak acid is determined by measuring the pH.

Similarly, the pOH of an equimolar basic buffer can be used to calculate the pKb of a weak base.

3. By altering the amounts of the salt and acid used for the buffer, you can make a buffer solution with the required pH.

When the proportions of the weak acid (or weak base) and the salts are roughly equal, buffer solutions are most efficient. This indicates that the acid’s pH is near to its pKa value (or pKb of the base).

Examples of Henderson Hasselbalch Equation

In chemical and biological systems, it gives the formula for pH value in terms of acidity.

To determine the pH of a buffer solution prepared by combining salt with a weak acid/base.

It’s how the pKa value is determined.

Make a pH-neutral buffer solution.

It’s mostly used to figure out how to compute a protein’s isoelectric point (the position at which a protein can neither accept nor yield protons).

With the direct formula, it is simple to compute the ionisation constants of strong acids and bases. However, because the extent of ionisation of weak acids and bases is so low, finding their ionisation constants with the same methods is challenging. The Henderson-Hasselbalch Equation comes in handy in such a case.

Conclusion 

When a little amount of acid or base is introduced or when the solution is diluted with pure solvent, a buffer is typically characterised as a solution that resists changes in pH. This characteristic is very beneficial for keeping the pH of a chemical system at an optimal level so that reaction kinetics and equilibrium processes can be influenced appropriately. A buffer solution is made up of a weak acid and its conjugate base, or a weak acid and its conjugate base. “Salts” is a term that refers to the conjugate forms. The Henderson-Hasselbalch equation is a particular form of the ionisation or dissociation constant expression. The pH of a solution that contains a weak acid as well as its conjugate base can be calculated using this equation (or salt). By partially neutralising a weak acid with a strong base, you can make a solution of the weak acid and its salt (conjugate base). To make the weak acid component, combine a surplus of salt with either a strong acid. The most common method for preparing a weak acid-conjugate base buffer would be to mix the weak acid with its salt directly. The concentrations of both weak acid and the strong acid may be precisely controlled with this third method.