pH Calculator

This tool calculates solution pH values based on the Brönsted and Lowry acid-base concept. This tool:

Strictly defines pH: pH = -log a[H+], where a[H+] is the activity of hydrogen ions (more accurately, hydrated protons H3O+ or hydrogen ions)

Considers ionic strength effects: Uses the Davies equation to calculate activity coefficients, suitable for solutions with ionic strength I below approximately 0.5 mol/L

Only calculates protonation-deprotonation equilibria: Focuses on instantaneous acid-base equilibria and ionic strength effects, without considering other types of chemical reactions or phase changes

Add multiple chemical components: Supports various chemical substances including acids, bases, salts, etc.

Set concentrations: Input the molar concentration (mol/L) for each component

Detailed results: Displays pH value and ionic strength information

Current Recipe:

Calculation Results:

pH: --

Models for calculating activity coefficients in electrolyte solutions are essential tools for predicting the effective concentration of ions. They vary based on ionic strength:

Debye–Hückel (limiting law): For very dilute solutions (I ≤ 0.01 M).

Davies equation: A simple, general-purpose model for moderate concentrations (I ≤ 0.5 M).

Extended Debye–Hückel: Offers improved accuracy for multivalent ions by including an ion size parameter.

Pitzer / SIT models: For high ionic strength solutions (I > 0.5 M), accounting for complex ion interactions.

These models are primarily for 25°C aqueous solutions, and parameter adjustments are needed for other conditions.

Reference: Ronteltap M, Maurer M, Gujer W. Struvite precipitation thermodynamics in source-separated urine. Water Res. 2007 Mar;41(5):977-84. doi: 10.1016/j.watres.2006.11.046. Epub 2007 Jan 25. PMID: 17258264.