1. What is pKa?

The pKa value is a quantitative measure of the strength of an acid in solution. It is the negative base-10 logarithm of the acid dissociation constant (Ka) for water solutions. ChemAxon provides accurate pKa calculations for various chemical compounds in aqueous solutions.

2. How Does the Calculator Work?

The calculator uses the fundamental pKa equation:

Where:

• \( K_a \) — Acid dissociation constant (mol/L)
• \( log_{10} \) — Base-10 logarithm

Explanation: The pKa value indicates the pH at which a chemical species will accept or donate protons. Lower pKa values indicate stronger acids.

3. Importance of pKa Calculation

Details: pKa values are crucial in pharmaceutical development, chemical synthesis, and biochemical studies as they affect solubility, absorption, and reactivity of compounds.

4. Using the Calculator

Tips: Enter the acid dissociation constant (Ka) in mol/L. The temperature field is optional (default is 25°C). All values must be valid (Ka > 0).

5. Frequently Asked Questions (FAQ)

Q1: What is the relationship between pKa and pH?
A: The Henderson-Hasselbalch equation relates them: pH = pKa + log([A⁻]/[HA]), where [A⁻] is conjugate base and [HA] is acid concentration.

Q2: What are typical pKa ranges?
A: Strong acids have pKa < 0, weak acids 0-10, and very weak acids >10. Water's pKa is 15.7 at 25°C.

Q3: How does temperature affect pKa?
A: pKa values are temperature-dependent. Most acids become slightly stronger (lower pKa) as temperature increases.

Q4: What's special about ChemAxon's pKa calculations?
A: ChemAxon uses advanced algorithms to predict pKa values based on molecular structure, accounting for electronic and steric effects.

Q5: Can this calculator handle multi-protic acids?
A: This basic version calculates single pKa values. For polyprotic acids, each dissociation has its own pKa value.