Henderson-Hasselbalch Equations

In this article we will discuss about the Henderson-Hasselbalch Equations.

This concerns the dissociation of weak acid in equi­librium.

Let us consider HA, a weak acid that ionizes as follows:

The above 1 no. equation is known as Henderson-Hassethalch equation.

Example:

In case of blood, the ratio between [BHCO₃]: [H₂CO₃] or [B₂HPO₄]: [BH₂PO₄] can be found out by applying the above equation to maintain aver­age pH of blood 7.4.

Application:

The equation can be to determine the pH of blood.

Importance:

1. With the help of this equation an indi­vidual is judged of his/her normal condi­tion when concentration of [BHCO₃] : [H₂CO₃] = 20: 1

Or, [B₂HPO₄] : [BH₂PO₄] = 4 : 1 at his/her of blood is 7.4.

If the above-mentioned ratios are altered the individuals are considered as suffer­ing from acidosis or alkalosis. They are treated with medicine according to the conditions (acidosis or alkalosis) to cure them to lead a normal life.

The table below gives the pH of some typi­cal solutions:

Effects of Temperature:

i. The pH of a solution may vary with tem­perature because ionisation is increased with the rise in temperature.

ii. Pure water at 22°C has pH 7.0 but at 38°C it has pH 6.74.

iii. The pH of a solution (e.g. N/10 HC1) which is completely ionised will not vary with the temperature.