What is Henderson-Hasselbalch?

Use this calculator to compute Henderson-Hasselbalch values with step-by-step solutions.

How do I use this calculator?

Enter the required values; results and step-by-step derivation update automatically.

Where is Henderson-Hasselbalch used?

Acid-Base Chemistry, engineering, research, and related disciplines.

What formulas does this use?

All standard henderson-hasselbalch formulas are applied and shown step-by-step in the results.

Can I get step-by-step solutions?

Yes. The calculator shows a full step-by-step derivation when results are displayed.

How accurate are the results?

Results use standard floating-point arithmetic (~15 significant digits). Suitable for education and professional use.

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PHYSICAL CHEMISTRYAcid-Base ChemistryChemistry Calculator

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Henderson-Hasselbalch: Buffer pH

pH = pKa + log₁₀([A⁻]/[HA]). Relates buffer pH to pKa and conjugate pair ratio. Effective range pKa ± 1. Essential for buffer design in biochemistry and pharmaceuticals.

Concept Fundamentals

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Ratio

—

Range

—

Capacity

Calculate Buffer pHpH = pKa + log([A⁻]/[HA])

Why This Chemistry Calculation Matters

Why: Henderson-Hasselbalch enables buffer design for labs, pharma, and biology. Predicts pH from ratio; designs buffers for target pH.

How: Enter pKa, [HA], [A⁻]. pH = pKa + log([A⁻]/[HA]). Or enter target pH to find ratio. Buffer range pKa ± 1.

●pH = pKa when [A⁻] = [HA].
●Buffer range: pKa ± 1.
●Higher concentration = greater capacity.

Sources:IUPAC Gold BookNIST pH Standards

Buffer Examples

🧪 Acetate Buffer pH 5

Common lab buffer - acetic acid/acetate

🩸 Blood Carbonate Buffer

Physiological pH 7.4 buffer system

⚗️ PBS Buffer pH 7.4

Phosphate buffered saline for biology

🧬 Tris Buffer pH 8.0

Common molecular biology buffer

📊 Find Ratio for pH 7.0

Calculate base/acid ratio needed

💨 Ammonia Buffer

High pH buffer system

🧫 HEPES Buffer pH 7.5

Zwitterionic buffer for cell culture

🍊 Citrate Buffer pH 5.0

Citric acid buffer system

🧬 Glycine Buffer pH 10.0

High pH amino acid buffer

⚖️ Half-Equivalence Point

pH = pKa when [A⁻] = [HA]

👁️ Borate Buffer pH 9.0

Eye wash and analytical chemistry

🔬 MOPS Buffer pH 7.2

Biological buffer for electrophoresis

🧪 PIPES Buffer pH 6.8

Piperazine-based buffer

🧂 Carbonate Buffer pH 10

High pH carbonate buffer

📚 Imidazole Buffer pH 7.0

Protein purification buffer

Calculate Buffer pH

Calculation Mode

Buffer System

pKaAcid dissociation constant

[HA] Acid Concentration (M)

[A⁻] Base Concentration (M)

For educational and informational purposes only. Verify with a qualified professional.

🔬 Chemistry Facts

⚗️

pH = pKa + log([A⁻]/[HA]). Henderson-Hasselbalch.

— IUPAC

⚡

At [A⁻]=[HA], pH = pKa. Half-equivalence.

— Buffer

🔬

Effective range pKa ± 1. Maximum capacity at pH=pKa.

— Physical

📐

Blood: HCO₃⁻/H₂CO₃. pH 7.4, ratio ~20:1.

— Physiology

The Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa of the weak acid and the ratio of conjugate base to weak acid concentrations. It's fundamental for buffer design in chemistry and biochemistry.

pH = pKa + log₁₀([A⁻]/[HA])

[A⁻] = conjugate base concentration, [HA] = weak acid concentration

Common Buffer Systems

Buffer System	Acid/Base	pKa	Optimal pH Range
Acetate	CH₃COOH / CH₃COO⁻	4.76	3.8-5.8
Phosphate (1st)	H₃PO₄ / H₂PO₄⁻	2.15	1.2-3.2
Phosphate (2nd)	H₂PO₄⁻ / HPO₄²⁻	7.2	6.2-8.2
Carbonate/Bicarbonate	H₂CO₃ / HCO₃⁻	6.35	5.4-7.4
Ammonia/Ammonium	NH₄⁺ / NH₃	9.25	8.3-10.3
Tris	Tris-H⁺ / Tris	8.07	7.1-9.1
HEPES	HEPES-H⁺ / HEPES	7.55	6.6-8.6
Citrate (2nd)	H₂Cit⁻ / HCit²⁻	4.76	3.8-5.8

Key Concepts

Buffer Range

Effective buffer range is pKa ± 1, where the buffer resists pH changes most effectively.

Half-Equivalence Point

When [A⁻] = [HA], the ratio is 1, log(1) = 0, so pH = pKa exactly.

Buffer Capacity

Higher total concentration = greater buffer capacity. Optimal when pH = pKa.

How Does the Henderson-Hasselbalch Equation Work?

The Henderson-Hasselbalch equation is derived from the acid dissociation equilibrium expression. It provides a convenient way to calculate pH when you know the ratio of conjugate base to weak acid concentrations.

🔬 Derivation from Ka

Starting Point

HA ⇌ H⁺ + A⁻

Ka = [H⁺][A⁻] / [HA]

Solving for [H⁺]:

[H⁺] = Ka × [HA] / [A⁻]

Taking Negative Logarithm

-log[H⁺] = -log(Ka) - log([HA]/[A⁻])

pH = pKa - log([HA]/[A⁻])

pH = pKa + log([A⁻]/[HA])

Henderson-Hasselbalch!

When to Use This Calculator

The Henderson-Hasselbalch equation is essential for anyone working with buffer solutions in laboratories, pharmaceutical development, or biological research.

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Molecular Biology

Prepare buffers for DNA/RNA work, enzyme assays, and cell culture.

Tris buffers (pH 7-9)
Phosphate buffers (pH 6-8)
HEPES buffers (pH 6.8-8.2)

💊

Pharmaceuticals

Formulate drug solutions, predict ionization, and optimize bioavailability.

IV solution preparation
Drug stability
Solubility optimization

🩺

Clinical Chemistry

Understand blood pH regulation and acid-base disorders.

Blood gas analysis
Bicarbonate buffer system
Acidosis/alkalosis diagnosis

The Bicarbonate Buffer System in Blood

The most important physiological buffer is the bicarbonate/carbonic acid system, which maintains blood pH at 7.35-7.45. The Henderson-Hasselbalch equation explains how this works.

pH = 6.1 + log₁₀([HCO₃⁻] / [H₂CO₃])

Normal Values

[HCO₃⁻] ≈ 24 mM

[H₂CO₃] ≈ 1.2 mM

Normal Ratio

20:1

Base to acid

Normal Blood pH

7.40

6.1 + log(20) = 7.4

Practical Buffer Preparation Examples

Example: Preparing Acetate Buffer at pH 5.0

Given:

pKa of acetic acid = 4.76
Target pH = 5.0
Total concentration = 0.1 M

Solution:

5.0 = 4.76 + log([A⁻]/[HA])

log([A⁻]/[HA]) = 0.24

[A⁻]/[HA] = 10^0.24 = 1.74

[Acetate] = 0.064 M, [Acetic acid] = 0.036 M

Example: PBS Buffer at pH 7.4