1. What is pKa?

pKa is the negative logarithm of the acid dissociation constant (Ka). It provides a convenient way to express the strength of an acid, with lower pKa values indicating stronger acids.

2. How Does the Calculator Work?

The calculator uses the pKa formula:

Where:

• \( pKa \) — Acid dissociation constant in logarithmic form (dimensionless)
• \( Ka \) — Acid dissociation constant (M)
• \( \log_{10} \) — Base-10 logarithm

Explanation: The pKa value represents the pH at which half of the acid molecules are dissociated. It's a logarithmic scale that makes it easier to work with very small Ka values.

3. Importance of pKa Calculation

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

4. Using the Calculator

Tips: Enter the acid dissociation constant (Ka) in molar units (M). The value must be positive and greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the relationship between pKa and pH?
A: pKa indicates the inherent strength of an acid, while pH measures the acidity of a solution. The Henderson-Hasselbalch equation relates them: pH = pKa + log([A⁻]/[HA]).

Q2: What pKa values indicate strong acids?
A: Strong acids typically have pKa values less than 0, while weak acids have pKa values greater than 0.

Q3: Can pKa be negative?
A: Yes, for very strong acids where Ka > 1, the pKa will be negative.

Q4: Why use logarithmic scale for Ka?
A: Ka values for weak acids can be extremely small (e.g., 1.8×10⁻⁵ for acetic acid), so pKa provides a more manageable scale.

Q5: How does temperature affect pKa?
A: pKa values are temperature-dependent, as Ka changes with temperature according to van't Hoff equation.