pKa Calculator

Calculate pKa from Ka, find Ka from pKa, or find pH from Ka. Measure acid strength instantly.

⚗️ pKa Calculator

Ka Value

⚠ Enter a valid positive value.

Common pKa Values

HF: pKa = 3.17Acetic: 4.76 H₂CO₃: 6.35NH₄⁺: 9.25 H₂O: 15.7HCl: –7

Formula

pKa = −log(Ka)

pKa

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⚗️ pKa Formula

pKa = −log₁₀(Ka)

Ka = 10^(−pKa)

pKa measures acid strength. Lower pKa = stronger acid. Strong acids (HCl, H₂SO₄) have negative pKa. Weak acids (acetic acid) have pKa around 4–6.

📖 Example

✅ Acetic Acid (CH₃COOH)

Ka = 1.8 × 10⁻⁵

pKa = −log(1.8×10⁻⁵) = 4.74

For 0.1 M solution: pH = ½(pKa − log C) = ½(4.74 − (−1)) = 2.87

❓ FAQ

What is Ka?

Ka is the acid dissociation constant. For HA ⇌ H⁺ + A⁻, Ka = [H⁺][A⁻]/[HA]. Larger Ka means stronger acid.

What is the difference between Ka and pKa?

pKa = −log(Ka). They measure the same thing — acid strength — but pKa is a more convenient logarithmic scale. Strong acids have small Ka and large negative pKa.

🔗 Related

Comprehensive Guide

Mastering pKa Calculations

Our free pKa Calculator simplifies complex chemistry mathematics, providing step-by-step clarity for analytical problem solving. Whether you're prepping for an AP Chemistry exam or working in a research lab, computing pKa quickly prevents cascading mathematical errors. Mastering the concepts behind pKa is crucial for understanding advanced chemical reactions and laboratory procedures.

Why is pKa Important?

In analytical chemistry, precision is everything. Having a reliable way to compute pKa saves time, prevents wasted materials, and ensures scientific accuracy.

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Speed

Instant

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Accuracy

100%

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Level

All Levels

Always verify your input units before calculating. Mismatched units (e.g., using mL instead of L) are the most common source of error when determining pKa!

Common Applications

Academic Study: Speeding up repetitive calculations.
Laboratory Practice: Ensuring exact stoichiometry for reactions.
Data Validation: Studying for college-level chemistry tests.

Relying solely on the calculator without understanding the underlying formula. Always review the step-by-step breakdown to internalize the mechanics.