Buffer Capacity & pH Drift Estimator
Model a weak acid–conjugate base buffer system (HA/A⁻) and simulate the effect of adding strong acids, strong bases, or pure water. See how pH drift depends on buffer capacity and perturbation size.
No Calculations Yet
Configure your buffer system and add perturbations to see how pH changes when strong acids or bases are added. Results will appear here with drift analysis and buffer capacity metrics.
Understanding Buffer Capacity & pH Drift
A buffer solution resists changes in pH when small amounts of acid or base are added. This resistance is quantified by buffer capacity (\u03B2), which measures how many moles of strong acid or base are needed to change the pH by one unit per liter of solution.
When you add a strong acid or base to a buffer, the pH will shift slightly. This shift is called pH drift (\u0394pH). A good buffer minimizes this drift, keeping the solution's pH stable for chemical or biological processes that require precise pH control.
Key Equations
Henderson-Hasselbalch Equation: Relates pH to the pKa of the weak acid and the ratio of conjugate base to acid concentrations.
Theoretical Buffer Capacity: Maximum at pH = pKa, where [HA] = [A\u207B] and the buffer can neutralize both acids and bases effectively.
Stoichiometric Reactions
Adding Strong Acid (H\u207A)
The H\u207A from the strong acid reacts with the conjugate base (A\u207B), converting it to weak acid (HA). This consumes the H\u207A and prevents large pH drops.
Adding Strong Base (OH\u207B)
The OH\u207B from the strong base reacts with the weak acid (HA), converting it to conjugate base (A\u207B). This consumes the OH\u207B and prevents large pH rises.
Worked Example
Add 5 mL of 0.1 M HCl to 100 mL of acetate buffer (0.1 M CH\u2083COOH + 0.1 M CH\u2083COO\u207B, pKa = 4.76)
The buffer successfully resisted pH change. Adding the same amount of HCl to pure water would drop pH from ~7 to ~2!
Effective Buffer Range
Buffers work best within \u00B11 pH unit of their pKa. Outside this range, the ratio of [A\u207B]/[HA] becomes extreme and buffer capacity drops significantly.
Limitations of This Tool
Assumes activity coefficients = 1. Real solutions at high ionic strength deviate from this assumption.
Uses Kw = 10\u207B\u00B9\u2074 (valid at 25\u00B0C). pKa values and Kw change with temperature.
Simple HA/A\u207B model. Polyprotic buffers (like phosphate) have multiple equilibria not fully captured here.
Strong acids and bases are assumed to completely dissociate, which is valid for dilute aqueous solutions.
Educational Use Only
This tool provides simplified calculations for learning about buffer systems and pH drift. Do NOT use for pharmaceutical formulation, clinical applications, industrial processes, or any situation requiring precise pH control. Professional laboratory work requires proper calibration, equipment, and validated methods.
Frequently Asked Questions
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