Science & Lab Tools
Henderson-Hasselbalch Calculator
Calculate the pH of buffer solutions using the Henderson-Hasselbalch equation
Reviewed by the calculator.uk.com Team · Last reviewed 16 August 2026 · Our methodology
Enter values to calculate buffer pH
Related to Henderson-Hasselbalch Calculator
The Henderson-Hasselbalch calculator uses the fundamental equation: pH = pKa + log10([A-]/[HA]) to determine the pH of buffer solutions. This equation, developed by Lawrence Joseph Henderson and later refined by Karl Albert Hasselbalch, is essential for understanding and preparing buffer solutions in chemistry and biochemistry.
The Equation Components
• pH: The negative logarithm of hydrogen ion concentration
• pKa: The negative logarithm of the acid dissociation constant
• [A-]: The concentration of the conjugate base
• [HA]: The concentration of the weak acid
The calculator takes three inputs: the pKa of the weak acid and the concentrations of both the weak acid [HA] and its conjugate base [A-]. It then calculates the pH using the Henderson-Hasselbalch equation and determines the ratio of conjugate base to acid, which is crucial for understanding the buffer's composition and capacity.
The calculator provides two key pieces of information: the pH of the buffer solution and the ratio of conjugate base to acid ([A-]/[HA]). Understanding these values is crucial for buffer preparation and analysis.
Key Relationships
• When pH = pKa, the ratio [A-]/[HA] = 1 (equal concentrations)
• When pH > pKa, there is more conjugate base than acid
• When pH < pKa, there is more acid than conjugate base
• For every pH unit change, the ratio changes by a factor of 10
The buffer capacity is highest when the ratio is close to 1, meaning the pH is near the pKa value. The effective buffering range typically extends to ±1 pH unit from the pKa, where the ratio ranges from 0.1 to 10.
1. What is a buffer solution?
A buffer solution is a mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists changes in pH when small amounts of acid or base are added. It maintains a relatively stable pH in chemical and biological systems.
2. When is the Henderson-Hasselbalch equation most accurate?
The equation is most accurate when: 1) The acid's pKa is between 2 and 12, 2) The concentrations of acid and base are between 0.1 M and 1 M, and 3) The ratio of concentrations is between 0.1 and 10.
3. Why do we need buffer solutions?
Buffer solutions are crucial in many applications, including biological systems (maintaining blood pH), chemical reactions that require specific pH conditions, and laboratory procedures where pH stability is essential for accurate results.
4. How do I choose the right buffer for my application?
Select a buffer system where the pKa is within 1 unit of your desired pH. Consider the buffer's capacity, temperature stability, and potential interactions with your system. Common buffers include acetate (pKa 4.76), phosphate (pKa 7.21), and TRIS (pKa 8.06).
5. What is the scientific source for this calculator?
Lawrence Henderson derived the underlying relationship between pH, pKa, and the acid-base concentration ratio in 1908; Karl Hasselbalch recast it in logarithmic form in 1916, giving the equation its familiar modern shape. Because it follows directly from the acid dissociation equilibrium constant, it appears in essentially every general and analytical chemistry textbook, and its scope of validity is examined in detail in Po and Senozan's 2001 Journal of Chemical Education review, "Henderson-Hasselbalch Equation: Its History and Limitations." This calculator applies that logarithmic form directly to the acid and conjugate base concentrations you enter.