When can you not use the Henderson-Hasselbalch equation?

The equation is not suitable when: – Dealing with strong acids or bases, as they fully dissociate and do not establish an equilibrium between the acid and its conjugate base. – The solution is highly concentrated, leading to significant deviations from ideal behavior due to activity coefficients differing from unity. – The pH is extremely low or high, where the assumptions of the equation break down. – The buffer components undergo additional reactions that affect the acid-base equilibrium.