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Calculate sulfuric acid pH with our easy online calculator. Enter H₂SO₄ concentration and get a fast pH result using acid equilibrium.
| Formula | Meaning |
|---|---|
| H₂SO₄ → H⁺ + HSO₄⁻ | First dissociation, treated as complete |
| HSO₄⁻ ⇌ H⁺ + SO₄²⁻, Ka₂ ≈ 0.012 | Second dissociation, treated as an equilibrium |
| x² + (C+Ka₂)x − Ka₂C = 0 | Rearranged equilibrium expression, solved for the positive root |
| pH = −log₁₀(C + x) | Final pH from total [H⁺] |
The sulfuric acid pH calculator helps you find the pH of an H₂SO₄ solution fast. Just enter the acid strength in mol/L. The tool then finds the hydrogen ion level and pH.
We developed this calculator so users can easily calculate sulfuric acid pH without doing long math by hand.
Sulfuric acid is a strong acid. Yet, its second proton does not fully split in water. So, a good pH result should include this second step.
Sulfuric acid has two acid steps.
First:
H₂SO₄ → H⁺ + HSO₄⁻
For an acid level of C mol/L:
[H⁺] ≈ C
The second step is:
HSO₄⁻ ⇌ H⁺ + SO₄²⁻
Use the second acid constant:
Ka₂ ≈ 0.0102
Then let x be the extra H⁺ from step two.
Ka₂ = ((C + x) × x) / (C − x)
The quadratic form is:
x = (−(C + Ka₂) + √((C + Ka₂)² + 4Ka₂C)) / 2
Then:
[H⁺] = C + x
The final sulfuric acid pH formula is:
pH = −log₁₀([H⁺])
This method includes the second acid step. That makes it better than the simple strong-acid shortcut.
It’s quick and handy for study, lab work, and basic solution checks.
Suppose you have a 0.010 M sulfuric acid solution.
First, set:
C = 0.010 M
Use:
Ka₂ = 0.0102
Now find x:
x = (−(0.010 + 0.0102) + √((0.010 + 0.0102)² + 4 × 0.0102 × 0.010)) / 2
This gives:
x ≈ 0.00448 M
Now find total H⁺:
[H⁺] = 0.010 + 0.00448
[H⁺] ≈ 0.01448 M
Now find pH:
pH = −log₁₀(0.01448)
pH ≈ 1.84
So, a 0.010 M sulfuric acid solution has an estimated pH of about 1.84 with this equilibrium model. A common classroom value of Ka₂ = 0.012 gives about pH 1.84 as well.
The sulfuric acid pH calculator makes H₂SO₄ pH math much easier. It uses the first acid step as complete. It then accounts for the second step with an equilibrium equation.
For very strong or very concentrated acid, real solutions can act in a more complex way. Activity effects can matter. So, treat this result as an aqueous equilibrium estimate.
It depends on its concentration. A stronger solution has a lower pH.
Yes. Its first acid step is very strong. Its second step is weaker.
The core formula is pH = −log₁₀([H⁺]). For H₂SO₄, you should first find total H⁺ while including the second acid step.
A commonly listed value is about 0.0102 at 25°C. This corresponds to a pKa₂ near 1.99.
For a quick estimate, yes. But the second acid step can affect the result. The equilibrium method gives a better estimate for dilute aqueous solutions.