Buffer Solution Calculator
Calculate buffer pH using the Henderson-Hasselbalch equation and visualize buffering capacity.
Dissociation constant of the acid.
Buffer Capacity Curve
Stable (flat) region = Best Buffering.
The Science of Chemical Balance
Buffers are the bodyguards of chemistry. They defend solutions against drastic pH changes, keeping biological systems alive and industrial processes stable.
The Equation
The Henderson-Hasselbalch equation is the golden rule for designing buffers. It connects the intrinsic strength of the acid (pKa) with the quantities you mix in the beaker.
The Seesaw Analogy
Imagine a seesaw balanced on the standard pH (the pKa).
- BalancedIf [Base] = [Acid], the log term is 0.
pH = pKa. This is the perfect buffer. - BasicIf [Base] > [Acid], the seesaw tips up.
pH > pKa. - AcidicIf [Acid] > [Base], the seesaw tips down.
pH < pKa.
Common Buffer Systems (at 25°C)
| Acid Name | Conjugate Base | pKa | Useful pH Range |
|---|---|---|---|
| Phosphoric Acid (H3PO4) | H2PO4- | 2.15 | 1.2 – 3.2 |
| Acetic Acid (CH3COOH) | Acetate (CH3COO-) | 4.76 | 3.8 – 5.8 |
| Carbonic Acid (H2CO3) | Bicarbonate (HCO3-) | 6.35 | 5.4 – 7.4 |
| Dihydrogen Phosphate | HPO42- | 7.20 | 6.2 – 8.2 |
| Ammonium (NH4+) | Ammonia (NH3) | 9.25 | 8.3 – 10.3 |
Human Blood
Your life depends on pH. Blood pH must stay between 7.35 and 7.45. The Carbonic Acid-Bicarbonate buffer system acts instantly to neutralize acids produced by metabolism or breathing, preventing acidosis or alkalosis.
Ocean Acidification
The ocean is a giant carbonate buffer (CO32-). However, as it absorbs excessive atmospheric CO2, the buffer capacity is being stretched, slowly lowering the pH and threatening coral reefs that rely on stable chemistry to build shells.
Fermentation
Brewers and winemakers rely on natural buffers in grains and grapes. Yeast enzymes are highly sensitive to pH; without buffering, the acid produced during fermentation would kill the yeast before the process is complete.
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Frequently Asked Questions
What is a Buffer Solution?
A buffer is an aqueous solution that resists changes in pH when small amounts of acid or base are added. It consists of a mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid).
What is the Henderson-Hasselbalch Equation?
It is the formula used to estimate the pH of a buffer solution: pH = pKa + log([Base]/[Acid]). It establishes the relationship between pH, pKa, and the ratio of conjugate base to weak acid.
What is pKa?
pKa is the negative logarithm of the acid dissociation constant ($K_a$). It represents the pH strength of an acid. A lower pKa indicates a stronger acid, meaning it gives up its protons more easily.
When is buffering capacity maximum?
Buffering capacity is at its peak when pH = pKa. At this point, the concentration of the weak acid [HA] is exactly equal to the concentration of its conjugate base [A-], allowing the buffer to neutralize added acid or base with equal efficiency.
What is the effective buffer range?
A buffer is generally effective within ±1 pH unit of its pKa. Outside this range, the ratio of acid to base becomes too skewed (greater than 10:1 or less than 1:10) to effectively resist pH changes.
How does the Blood Buffer System work?
Human blood uses the Bicarbonate Buffer System (H2CO3 / HCO3-). Carbon dioxide (CO2) dissolves to form carbonic acid, which balances with bicarbonate ions to keep blood pH strictly between 7.35 and 7.45.
Does dilution affect buffer pH?
Theoretically, no. Since pH depends on the ratio of [Base]/[Acid], if you dilute the solution, both concentrations decrease by the same factor, so the ratio stays the same. However, buffering capacity decreases with dilution.
How do I choose the right buffer?
Choose a weak acid with a pKa value closest to your target pH. For example, if you need a pH of 4.8, Acetic Acid (pKa 4.76) is an ideal choice.
What is the difference between Ka and pKa?
$K_a$ is the equilibrium constant for dissociation. $pKa$ is simply -log(Ka). Chemists prefer pKa because it provides convenient numbers (like 4.76) instead of tiny scientific notation values (like 1.74 × 10-5).
Can I make a buffer with a strong acid?
No. Strong acids (like HCl) dissociate completely, so there is no equilibrium between the acid and a conjugate base to 'soak up' added ions. Buffers MUST require a weak acid or base.
What does [A-] and [HA] stand for?
[HA] is the concentration of the proton donor (the weak acid). [A-] is the concentration of the proton acceptor (the conjugate base, usually added as a salt).
Why is the Log term important?
The log term adjusts the pH based on the ratio. If you have 10 times more base than acid, the pH goes up by 1 unit ($log(10) = 1$). If you have 10 times more acid, the pH drops by 1 unit ($log(0.1) = -1$).
What happens if I add strong base to a buffer?
The strong base (OH-) reacts with the weak acid (HA) to form water and more conjugate base (A-). The ratio [A-]/[HA] increases slightly, causing only a tiny rise in pH.
What is the Common Ion Effect?
It describes how adding a salt containing a common ion (like adding Sodium Acetate to Acetic Acid) suppresses the ionization of the weak acid, which is the fundamental principle behind how buffers are created.
Can temperature affect a buffer?
Yes. $K_a$ (and thus pKa) is temperature-dependent. This means the pH of a buffer can shift changes if the temperature changes significantly, which is critical in precise biological experiments.