How to Calculate Ka of Strong Acid

Strong Acid Dissociation:

\[ HA \rightarrow H^+ + A^- \] \[ Ka \approx 10^7 \text{ (for strong acids)} \]

Acid Concentration:

mol/L

Acid Type:

Acid Dissociation Constant (Ka):

pH Value:

Hydrogen Ion Concentration:

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1. What is Ka of Strong Acid?

The acid dissociation constant (Ka) measures the strength of an acid in solution. For strong acids, Ka values are very large (typically around 10⁷), indicating complete dissociation in water. Strong acids fully ionize, making Ka calculations straightforward compared to weak acids.

2. How Does the Calculator Work?

The calculator uses the principle of complete dissociation for strong acids:

\[ HA \rightarrow H^+ + A^- \] \[ Ka = \frac{[H^+][A^-]}{[HA]} \approx 10^7 \] \[ pH = -\log_{10}[H^+] \]

Where:

\( Ka \) — Acid dissociation constant (≈10⁷ for strong acids)
\( [H^+] \) — Hydrogen ion concentration (equal to acid concentration)
\( [A^-] \) — Conjugate base concentration
\( [HA] \) — Undissociated acid concentration (negligible for strong acids)
\( pH \) — Measure of acidity

Explanation: Strong acids completely dissociate in aqueous solution, so [H⁺] equals the initial acid concentration, and Ka is effectively infinite for practical purposes.

3. Importance of Ka Calculation

Details: Understanding Ka values helps predict acid strength, calculate pH, design buffer solutions, and understand chemical equilibrium in acid-base reactions.

4. Using the Calculator

Tips: Enter the concentration of your strong acid in mol/L and select the acid type. The calculator will show the approximate Ka value (10⁷), calculated pH, and hydrogen ion concentration.

5. Frequently Asked Questions (FAQ)

Q1: Why is Ka so large for strong acids?
A: Strong acids completely dissociate in water, making the numerator [H⁺][A⁻] very large compared to the denominator [HA], which is essentially zero.

Q2: What are common strong acids?
A: HCl, H₂SO₄, HNO₃, HBr, HI, HClO₄ are the six common strong acids that completely dissociate in water.

Q3: Can Ka be measured directly for strong acids?
A: No, because the dissociation is complete and equilibrium lies far to the right. Ka values for strong acids are estimated rather than measured.

Q4: How does concentration affect strong acid pH?
A: pH decreases logarithmically as concentration increases: pH = -log₁₀[C], where C is the acid concentration.

Q5: What's the difference between strong and weak acids?
A: Strong acids completely dissociate (Ka > 1), while weak acids partially dissociate (Ka < 1) and establish equilibrium.