1. What is the Weak Acid pH Formula?

The weak acid pH formula calculates the pH of a solution containing a weak acid based on its dissociation constant (Ka) and concentration (C). This formula provides an approximation of the solution's acidity level.

2. How Does the Calculator Work?

The calculator uses the weak acid pH formula:

Where:

• \( K_a \) — Acid dissociation constant (mol/L)
• \( C \) — Concentration of the weak acid (mol/L)

Explanation: The formula assumes that the acid is weak enough that the concentration of H⁺ ions is approximately equal to the square root of Ka times C.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for understanding acid-base chemistry, predicting chemical behavior, and applications in biological systems, industrial processes, and environmental science.

4. Using the Calculator

Tips: Enter the acid dissociation constant (Ka) in mol/L and the concentration (C) in mol/L. Both values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What defines a "weak acid"?
A: A weak acid is one that doesn't completely dissociate in water, typically with Ka values less than 1.

Q2: When is this approximation valid?
A: This approximation works best when Ka is significantly smaller than the concentration C (Ka << C).

Q3: What are typical Ka values for common weak acids?
A: Acetic acid: 1.8×10⁻⁵, Formic acid: 1.8×10⁻⁴, Hydrocyanic acid: 4.9×10⁻¹⁰.

Q4: Are there limitations to this formula?
A: This formula assumes the acid is monoprotic and that autoionization of water is negligible. It may not be accurate for very dilute solutions or very strong weak acids.

Q5: How does temperature affect the calculation?
A: Ka values are temperature-dependent, so the calculation should use Ka values measured at the appropriate temperature.