Strong Acid pH Calculator

Calculate pH of strong acid solutions (HCl, HBr, HNO3, H2SO4). Strong acids fully dissociate so pH = -log(concentration). Handle both monoprotic and diprotic cases.

🔬 Acid-Base📐 pH = -log[H⁺] = -log(C for monoprotic)🧪 Chemistry
Concentration C (mol/L)
Acid type
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Formula & Reference

VariableSymbolFormulaUnits
Strong Acid pH Calculator—pH = -log[H⁺] = -log(C for monoprotic)pH

Step-by-Step Examples

Example 1
0.010 M HCl

HCl is strong acid, fully dissociates. 0.010 M HCl.

  • [H+] = 0.010 M
  • pH = -log(0.010) = 2.00
✓ pH = 2.00
Example 2
0.050 M H2SO4

H2SO4 first dissociation complete (n~2). 0.050 M H2SO4.

  • [H+] ~ 2 x 0.050 = 0.100 M (first H fully, second partially)
  • pH ~ -log(0.100) = 1.00
  • Note: second H+ partially contributes; true pH slightly above 1.00
✓ pH ~ 1.00 (monoprotic approximation for first dissociation)
Example 3
Dilute HNO3

1.5x10^-4 M HNO3.

  • [H+] = 1.5x10^-4 M
  • pH = -log(1.5x10^-4) = 3.82
✓ pH = 3.82

Real-World Applications

🧪
Lab Acid Preparation
Know exact pH when making acidic solutions for reactions and titrations.
🏭
Industrial Processes
Etching, pickling, cleaning use strong acid. pH control is critical for process safety.
💊
Gastric Chemistry
Stomach HCl: pH 1.5-2.0. Full acid output ~ 0.03-0.10 M HCl.
⚗️
Titration
Starting pH for strong acid titration; calculate full curve from initial pH.

Common Mistakes to Avoid

⚠️
pH = -log(C) only for strong acids

This shortcut works ONLY for fully dissociating acids. Never use pH = -log(C) for weak acids like acetic acid.

⚠️
At very low C: water contribution matters

Below 10^-7 M: water [H+] becomes significant. pH approaches 7 (neutral), not 7+. Use quadratic: [H+]^2 + C[H+] - Kw = 0 for dilute acid.

⚠️
H2SO4 is only partly diprotic in practice

First dissociation complete; second Ka2 = 0.012 (somewhat weak). Approximation n=2 overestimates [H+] slightly.

Frequently Asked Questions

What are common strong acids? ▾
HCl, HBr, HI, HNO3, H2SO4 (first dissociation), HClO4, HClO3. They fully dissociate in water. [H+] = C (monoprotic) or 2C (diprotic approximation).
What is the pH of concentrated HCl? ▾
Concentrated HCl: 12 M. pH = -log(12) = -1.08 (negative pH!). pH < 0 is physically real for very concentrated acids.
Why can concentrated H2SO4 have pH near -3? ▾
pH = -log[H+]. At 18 M H2SO4: [H+] >> 1. Activity effects compound this. pH = -3 to -2 for pure H2SO4.
When does a 1x10^-8 M HCl give pH = 7? ▾
A 10^-8 M HCl solution gives pH just slightly below 7 (not 8). Water contributes 10^-7 M H+, dominating the acid. Correct calculation: ~6.996.
What is the difference between concentrated and dilute acid? ▾
Concentrated: high molarity (12 M HCl). Dilute: low molarity (0.01 M HCl). Both strong: fully dissociated. Only concentration differs.

Related Chemistry Calculators

🔬 pH Calculator🔬 Weak Acid pH🔬 Titration🔬 Ka Calculator🔬 pOH Calculator

Formula Explorer connections

Interpretation: This relationship connects hydrogen-ion activity, dissociation, conjugate ratios or titration stoichiometry to acid–base behavior. Assumption: Concentration approximates activity mainly in dilute solutions. Temperature, ionic strength, acid strength and equilibrium approximations affect accuracy.

Titration Calculator →Titration Endpoint & Indicator Calculator →Weak Acid pH Calculator →Chemistry Formula Explorer →