1. What is the Acid Dissociation Constant (Ka)?

The acid dissociation constant (Ka) is a quantitative measure of the strength of an acid in solution. It represents the equilibrium constant for the dissociation reaction of an acid into its conjugate base and a proton (H⁺ ion).

2. How Does the Calculator Work?

The calculator uses the acid dissociation formula:

Where:

• \( K_a \) — Acid dissociation constant (mol/L)
• \( [H^+] \) — Hydrogen ion concentration = 10^(-pH) (mol/L)
• \( C \) — Initial molar concentration of the acid (mol/L)

Approximation: When \( [H^+] \ll C \), the formula simplifies to \( K_a \approx \frac{[H^+]^2}{C} \)

3. Importance of Ka Calculation

Details: Ka values help determine acid strength, predict acid-base reaction outcomes, and understand buffer systems in chemistry and biochemistry.

4. Using the Calculator

Tips: Enter pH value (0-14) and initial acid molarity (must be > 0). The calculator automatically determines whether to use the exact or approximate formula based on the concentration values.

5. Frequently Asked Questions (FAQ)

Q1: What does a larger Ka value indicate?
A: A larger Ka value indicates a stronger acid, meaning it dissociates more completely in solution.

Q2: When is the approximation formula valid?
A: The approximation \( K_a \approx \frac{[H^+]^2}{C} \) is valid when \( [H^+] < 0.05C \), meaning less than 5% dissociation.

Q3: How is pKa related to Ka?
A: pKa = -log(Ka). Smaller pKa values indicate stronger acids.

Q4: What are typical Ka values for common acids?
A: Strong acids have Ka > 1, weak acids have Ka < 1. For example, acetic acid Ka ≈ 1.8 × 10⁻⁵.

Q5: Can this calculator be used for polyprotic acids?
A: This calculator is designed for monoprotic acids. Polyprotic acids have multiple Ka values for each dissociation step.