# How to Calculate pH and pKa of a Buffer using Henderson-Hasselbalch Equation?

Henderson-Hasselbalch equation is a numerical expression which relates the * pH, pKa* and

*of a buffer. A buffer is a solution which can resist the change in*

**B****uffer Action***pH.*Chemically, a buffer is a solution of equimolar concentration of a weak acid (such as acetic acid – CH

_{3}COOH) and its conjugate base (such as acetate ion – CH

_{3}COO¯). In the previous post, we have discussed the

**Titration Curve**of a weak acid and the

**Derivation of Henderson-Hasselbalch Equation**. The characteristic shape of the titration curve of a weak acid is also described by the Henderson-Hasselbalch equation. In this chapter we will discuss the methods to calculate the

*or*

**pH***of a buffer using Henderson-Hasselbalch equation using sample problems.*

**pKa****Learn more:** Titration Curve of a Weak Acid (Acetic Acid)

**Lean more:** How to Derive Henderson-Hasselbalch Equation?

Henderson-Hasselbalch Equation is given as:

Where,

* pH *– the negative logarithm of H⁺ ion concentration in the medium.

* pKa* – the negative logarithm of

*Ka*of the acid

*(Ka*is the dissociation constant)

* Proton acceptor* – the ionized or deprotonated acid (example – CH

_{3}COO¯).

* Proton donor* – intact (non-ionized) weak acid (example – CH

_{3}COOH).

Let’s see some sample problems and solutions.

*Problem-1:* A mixture of 0.20M acetic acid and 0.30M sodium acetate is given. Calculate the pH of the medium if the pKa of the acetic acid is 4.76.