Acid Base Mixture pH Estimator

Compute approximate pH for mixtures of strong/weak acids and bases. Supports M, mM, µM concentrations and pKa/pKb inputs. Runs entirely offline—your data stays on your device.

Educational only. Follow your lab SOPs and SDS.

Input Components

Type

Concentration

pKa (for weak acid) or pKb (for weak base)

Type

Concentration

pKa (for weak acid) or pKb (for weak base)

Decimal Precision

Results

Estimated pH

7.000

Neutral (equal strong acid/base)

Intermediate Values

Net [H⁺] from strong

0.0000 M

Weak acid contribution

0.0000 M

Weak base contribution

0.0000 M

Ionic strength (approx.)

0.0000 M

Export for Notebook

Mixture: 0.100 M weak acid (pKa=4.76) + 0.050 M strong base.
Net strong effect: -0.050 M (excess base)
Estimated pH: 12.000 (approx., neglecting weak acid at high pH)
Ionic strength: 0.150 M

Why Estimate pH for Mixtures?

In lab work, you often mix solutions—buffer preparation, quenching reactions, or accidental spills. Predicting pH helps anticipate reactivity, safety risks, and analytical interference. This tool uses a simplified charge‑balance approach suitable for educational and planning purposes.

How to Use This Tool

Select the type (strong/weak acid/base) for each component.
Enter concentration (M, mM, or µM). Use scientific notation (1e‑3) or comma/decimal.
For weak species, provide pKa (acid) or pKb (base). Strong species ignore this field.
Click Calculate. Review warnings about dominance and approximation limits.
Use the export text for your lab notebook.

Real‑World Examples

Scenario	Component 1	Component 2	Expected pH
Buffer + strong base	0.1 M CH₃COOH (pKa=4.76)	0.02 M NaOH	~4.94
Acid spill neutralization	0.5 M HCl	0.3 M NH₃ (pKb=4.75)	~1.00 (strong acid dominates)
Weak acid‑base pair	0.01 M HCOOH (pKa=3.75)	0.005 M NaHCOO	~3.75 (Henderson‑Hasselbalch)

Common Mistakes Checklist

Using pKa for a base or pKb for an acid (they are related: pKa + pKb = 14 at 25°C).
Forgetting to convert mM to M (1 mM = 0.001 M).
Assuming weak acids/bases contribute significantly when a strong counterpart is in large excess.
Neglecting dilution effects when mixing volumes (this tool assumes instant mixing at given concentrations).

What‑If: Vary Strong Base Concentration

Hold the weak acid fixed and see how adding strong base changes pH. This mimics a titration planning step.

Strong Base [OH⁻] (M)

0.000 0.050 0.100 0.150 0.200

Resulting pH

12.000

Dominant Species

Excess OH⁻

Frequently Asked Questions

How accurate is this estimator?

Within ±0.2 pH units for simple mixtures under 0.1 M ionic strength. It ignores activity coefficients, temperature variation beyond 25°C, and complex formation. Always measure pH with a calibrated meter for critical work.

When do the approximations fail?

For very concentrated solutions (>1 M), polyprotic systems, amphoteric species, or when the pH is very close to the pKa of a weak component. Also, strong‑acid/strong‑base mixtures near neutrality are sensitive to impurities.

What about mixed solvents or high temperature?

This tool assumes aqueous solutions at 25°C (Kw=1×10⁻¹⁴). For mixed solvents, the autoprotolysis constant changes; for other temperatures, adjust Kw and pKa/pKb values accordingly.

Safety note for concentrated acids/bases?

Always add acid to water (not water to acid), use appropriate PPE (gloves, goggles, lab coat), and have a neutralization plan. Consult SDS for each chemical.

Formulas & Assumptions

Charge balance: [H⁺] + [B⁺] = [OH⁻] + [A⁻] (simplified for monoprotic species).
Strong acids/bases: Fully dissociated, contribute directly to [H⁺] or [OH⁻].
Weak acid: [A⁻] = Ka·[HA]/(Ka+[H⁺]), where Ka = 10⁻pKa.
Weak base: [BH⁺] = Kb·[B]/(Kb+[OH⁻]), with Kb = 10⁻pKb.
Water autoionization: Kw = [H⁺][OH⁻] = 1×10⁻¹⁴ at 25°C.
Ionic strength (approx.): I = 0.5·Σ(cᵢ·zᵢ²), used only for qualitative warnings.
Rounding: pH shown to selected decimal places; intermediate values keep 4 significant figures.

Disclaimer: For informational and educational purposes only. Estimates depend on your inputs and simplifying assumptions. This tool does not replace professional judgment, lab SOPs, or safety procedures. Always follow SDS guidance and institutional policies.

Sources: Common chemistry constants: R, NA, F; Standard unit conversions and lab measurement best practices; General analytical chemistry and uncertainty concepts; Intro physical chemistry relationships (ideal gas, Arrhenius, equilibrium); Laboratory safety basics and SDS principles.

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Acid Base Mixture pH Estimator

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