Buffer pH Calculator

A buffer is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid. It resists changes in pH when small quantities of an acid or an alkali are added to it.

pKa is the negative base-10 logarithm of the acid dissociation constant (Ka) of a solution. The lower the pKa, the stronger the acid. For a buffer, the pKa represents the pH at which the acid and its conjugate base are present in equal concentrations.

pKa values are chemical constants that can be found in chemistry textbooks, chemical handbooks (like the CRC Handbook of Chemistry and Physics), or online chemical databases.

A strong acid completely dissociates (ionizes) in water (e.g., HCl → H⁺ + Cl⁻). A weak acid only partially dissociates, creating an equilibrium between the acid and its conjugate base (e.g., CH₃COOH ⇌ H⁺ + CH₃COO⁻).

It provides a direct mathematical link between the pH of a solution and the relative amounts of the weak acid and conjugate base. It is the fundamental equation for designing and understanding buffer solutions.

Buffering capacity is a measure of a buffer's ability to resist pH change. It is highest when pH = pKa (i.e., when [A⁻] = [HA]), and the buffer is most effective within a range of pKa ± 1 pH unit.

Yes. The equation can be rearranged to solve for pKa: pKa = pH - log([A⁻]/[HA]). This is a common way to experimentally determine the pKa of an unknown weak acid.

Yes. You can use the pKa of the conjugate acid. For example, for an ammonia buffer (NH₃ / NH₄⁺), you would use the pKa of the ammonium ion (NH₄⁺), which is about 9.25.

The equation depends on the *ratio* of [A⁻] to [HA]. So, if you enter a ratio (e.g., 2 for the base and 1 for the acid), the calculated pH will be correct. However, the buffering capacity will depend on the actual concentrations.

A pH meter's electrode performance can drift over time. Calibration with standard buffer solutions of known pH (e.g., 4, 7, 10) ensures that the meter's readings are accurate and reliable.

Phosphate-buffered saline (PBS) and Tris-HCl are two of the most common buffers. PBS is used to maintain a physiological pH (~7.4) for cell work, while Tris is widely used in molecular biology for applications like electrophoresis.

Yes, significantly. The pKa of many common buffer substances changes with temperature. For example, the pKa of Tris decreases about 0.03 units for every 1°C increase. It's crucial to prepare the buffer at the temperature at which you will use it.

Ionic strength is a measure of the total concentration of ions in a solution. At high ionic strengths, the "activity" of ions is not equal to their concentration, which can cause the measured pH to deviate slightly from the value predicted by the Henderson-Hasselbalch equation.

First, choose a buffer with a pKa close to your target pH. Second, ensure the buffer components do not interfere with your experiment (e.g., phosphate can inhibit some enzymatic reactions).

It is generally not recommended unless you are creating a "universal buffer" with a very wide range, as the interactions can be complex and unpredictable.

pH is the negative log of the hydrogen ion [H⁺] concentration. pOH is the negative log of the hydroxide ion [OH⁻] concentration. In any aqueous solution at 25°C, pH + pOH = 14.

Buffers rely on the equilibrium between a weak acid and its conjugate base. A strong acid completely dissociates, so there is no equilibrium to shift to absorb added acid or base.

You can dissolve the weak acid in water and then add a strong base (like NaOH) until the pH meter shows your desired pH. At this point, you will have converted some of the weak acid (HA) into its conjugate base (A⁻), creating the buffer system.

While the pH depends on the *ratio* of the components, the final concentrations (and thus buffering capacity) depend on the final volume. It's good practice to use a volumetric flask for accuracy.

You can use it to understand the principle. However, the blood buffering system is much more complex, involving dissolved CO₂ and interactions with hemoglobin. This calculator is for simple, in-vitro buffer preparation.

No. This is an educational tool. Pharmaceutical buffers must be prepared according to strict Good Manufacturing Practice (GMP) standards and regulatory guidelines.

If they are in the same final volume, you can simply enter the number of moles for each component in the concentration fields. The ratio will be correct, and the calculated pH will be accurate.

For any laboratory procedure, consult your lab's established protocols. If you face issues, speak with your lab manager, supervisor, or a more experienced colleague.

Common reasons include: the pH meter is not calibrated, the temperature is different from the temperature at which the pKa was determined, impurities in reagents, or incorrect measurements of volumes or masses.

Yes. All calculations are performed entirely within your web browser. No data is sent to our servers, ensuring complete confidentiality.