1. What is Concentration of Weak Acid?

Definition: This calculator determines the concentration of a weak acid (HA) based on the concentrations of its dissociated ions (H+ and A-) and its dissociation constant (Ka).

Purpose: It helps chemists and students understand acid-base equilibria and calculate unknown concentrations in weak acid solutions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( HA \) — Concentration of weak acid (mol/m³)
• \( [H^+] \) — Concentration of hydrogen ion (mol/m³)
• \( [A^-] \) — Concentration of anion (mol/m³)
• \( K_a \) — Acid dissociation constant (dimensionless)

Explanation: The product of ion concentrations divided by the dissociation constant gives the original weak acid concentration.

3. Importance of Weak Acid Calculations

Details: Understanding weak acid concentrations is crucial for buffer preparation, pH control in chemical processes, and biological systems.

4. Using the Calculator

Tips: Enter the hydrogen ion concentration, anion concentration (both in mol/m³), and the Ka value. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical Ka value for weak acids?
A: Weak acids typically have Ka values between 10^-2 and 10^-12. For example, acetic acid has Ka = 1.8 × 10^-5.

Q2: How do I find [H+] and [A-] concentrations?
A: These can be measured experimentally (pH meter for [H+]) or calculated from known equilibrium conditions.

Q3: Can I use different concentration units?
A: Yes, but all concentrations must use the same units (e.g., all mol/L or all mol/m³).

Q4: Does this work for polyprotic acids?
A: This formula is for monoprotic acids. Polyprotic acids require more complex calculations.

Q5: What if my Ka value is very small?
A: Use scientific notation (e.g., enter 1.8E-5 for 1.8 × 10^-5) for best results.