1. What is pKa?

The pKa is the negative base-10 logarithm of the acid dissociation constant (Ka) of a solution. It provides a quantitative measure of the strength of an acid in solution, with lower pKa values indicating stronger acids.

2. How Does the Calculator Work?

The calculator uses the pKa formula:

Where:

• \( pKa \) — Acid dissociation constant on logarithmic scale
• \( Ka \) — Acid dissociation constant (dimensionless)

Explanation: The pKa value indicates the pH at which half of the acid molecules are dissociated. The logarithmic scale compresses the wide range of Ka values into more manageable numbers.

3. Importance of pKa Calculation

Details: pKa values are crucial in chemistry, biochemistry, and pharmacology for predicting acid-base behavior, drug absorption, protein binding, and chemical reactivity.

4. Using the Calculator

Tips: Enter the Ka value (must be positive). The calculator will compute the corresponding pKa value. For very small Ka values, scientific notation may be needed (e.g., 1.0E-10).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between pKa and pH?
A: pH measures the acidity of a solution, while pKa measures the inherent strength of an acid (its tendency to donate protons).

Q2: What are typical pKa values?
A: Strong acids have pKa < 0, weak acids 0-14, and very weak acids >14. Most biological acids have pKa values between 2-12.

Q3: How does pKa relate to buffer capacity?
A: A buffer works best when pH is within ±1 unit of its pKa. This is when the acid and conjugate base are present in significant amounts.

Q4: Can pKa be negative?
A: Yes, for very strong acids (Ka > 1). For example, hydrochloric acid (HCl) has a pKa of about -6.3.

Q5: How does temperature affect pKa?
A: pKa values are temperature-dependent, typically decreasing by about 0.01 units per °C increase for carboxylic acids.