1. What is the Acid Dissociation Constant?

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: HA ⇌ H⁺ + A⁻, where HA is the weak acid, H⁺ is the hydrogen ion, and A⁻ is the conjugate base.

2. How Does the Calculator Work?

The calculator uses the acid dissociation constant equation:

Where:

• \( K_a \) — Acid dissociation constant (mol/L)
• \( [H^+] \) — Hydrogen ion concentration (mol/L)
• \( [A^-] \) — Conjugate base concentration (mol/L)
• \( [HA] \) — Weak acid concentration (mol/L)

Calculation Steps:

1. Calculate [H⁺] from pH using: [H⁺] = 10^(-pH)
2. Substitute values into Kₐ equation
3. Calculate the acid dissociation constant

3. Importance of Kₐ Calculation

Details: The acid dissociation constant is crucial for understanding acid strength, predicting acid-base behavior, calculating pH of solutions, and designing buffer systems in chemistry and biochemistry.

4. Using the Calculator

Tips: Enter pH value (0-14), [A⁻] concentration in mol/L, and [HA] concentration in mol/L. Ensure all values are positive and pH is within the valid range.

5. Frequently Asked Questions (FAQ)

Q1: What is the relationship between pH and [H⁺]?
A: pH = -log₁₀[H⁺], so [H⁺] = 10^(-pH). This inverse logarithmic relationship means each unit change in pH represents a tenfold change in hydrogen ion concentration.

Q2: What do different Kₐ values indicate?
A: Larger Kₐ values indicate stronger acids (more dissociation), while smaller Kₐ values indicate weaker acids. Strong acids have Kₐ > 1, weak acids have Kₐ < 1.

Q3: How is pKₐ related to Kₐ?
A: pKₐ = -log₁₀Kₐ. This relationship is similar to pH and [H⁺], where smaller pKₐ values indicate stronger acids.

Q4: When is this calculation most accurate?
A: This calculation is most accurate for weak acids in dilute solutions where activity coefficients are close to 1 and where the acid concentration significantly exceeds [H⁺].

Q5: Can this be used for polyprotic acids?
A: For polyprotic acids, each dissociation step has its own Kₐ value (Kₐ₁, Kₐ₂, etc.). This calculator calculates Kₐ for the first dissociation step.