How To Calculate Concentration Of Weak Acid From Titration Curve

At Half-Equivalence: [HA] = K_a (for pH = pK_a)

\[ [HA] = K_a \]

[HA] (Weak Acid Concentration at Buffer Point):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What Is Weak Acid Concentration From Titration Curve?

The concentration of a weak acid can be determined from its titration curve, particularly at the half-equivalence point where pH equals pK_a and the concentration of the weak acid equals its acid dissociation constant.

2. How Does The Calculator Work?

The calculator uses the relationship at half-equivalence point:

\[ [HA] = K_a \]

Where:

\( [HA] \) — Concentration of weak acid at half-equivalence point (mol/L)
\( K_a \) — Acid dissociation constant (mol/L)

Explanation: At the half-equivalence point in a weak acid-strong base titration, exactly half of the weak acid has been neutralized. At this point, pH = pK_a and the concentration of the weak acid equals its acid dissociation constant.

3. Importance Of Half-Equivalence Point Calculation

Details: Determining weak acid concentration from titration curves is essential for characterizing acid strength, calculating buffer capacity, and understanding acid-base equilibrium in analytical chemistry and biochemistry.

4. Using The Calculator

Tips: Enter the acid dissociation constant (K_a) in mol/L. The value must be positive and non-zero. The calculator will determine the weak acid concentration at the half-equivalence point.

5. Frequently Asked Questions (FAQ)

Q1: Why does [HA] equal K_a at half-equivalence point?
A: At half-equivalence, [HA] = [A^-], so from the Henderson-Hasselbalch equation: pH = pK_a + log([A^-]/[HA]) = pK_a, meaning [HA] = K_a.

Q2: What is the significance of the half-equivalence point?
A: It represents the point of maximum buffer capacity and allows direct determination of the acid's pK_a value from the titration curve.

Q3: Can this method be used for all weak acids?
A: Yes, this relationship holds for all monoprotic weak acids undergoing titration with strong bases.

Q4: How accurate is this calculation?
A: Very accurate for ideal conditions, but real-world factors like ionic strength and temperature may introduce minor variations.

Q5: What if I have diprotic or polyprotic acids?
A: For polyprotic acids, each equivalence point corresponds to a different proton, and the calculation becomes more complex with multiple K_a values.