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Index/Physical chemistry/CHM-18

CHM-18

pH = −log10 a(H+)

pH = −log10 aH. Pedagogue: activity ≈ molarity in dilute water.

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Acid–baseSørensen 1909

Governing equation

pH=−log⁡10a(H+)\mathrm{pH}=-\log_{10}a(\mathrm{H}^+)

where

a(\mathrm{H}^+)
Proton activity (—)
pH
pH (—)

Lecture brief

Historical brief

Ideal-gas law, van ’t Hoff, Nernst, Michaelis–Menten and Clausius–Clapeyron are physical chemistry’s working equations of equilibrium and rate. The lab is pressure, potential and kinetics. This sheet (CHM-18 — pH = −log10 a(H+)) is the form associated with Sørensen 1909. Working symbols: a(H+)a(\mathrm{H}^+) →\rightarrow pHpH. Defined on the activity of the proton. At 25 °C, pH + pOH = 14 for pure water.

Purpose

Purpose: compute pHpH from a(H+)a(\mathrm{H}^+) in Physical chemistry via pH=−log⁡10a(H+)\mathrm{pH}=-\log_{10}a(\mathrm{H}^+) pH = −log10 aH. Pedagogue: activity ≈ molarity in dilute water. Use it when a real physical chemistry question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given a(H+)=1.000e−7 —a(\mathrm{H}^+) = 1.000e-7\,\mathrm{—}, the governing relation pH=−log⁡10a(H+)\mathrm{pH}=-\log_{10}a(\mathrm{H}^+) yields pH=7.000 —pH = 7.000\,\mathrm{—}. Dilute aqueous, activity coefficient ≈ 1. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Outputs

  • pH pH7.000 —
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CHM-18 · gauge
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Narration of this film

Dilute aqueous, activity coefficient ≈ 1.

Defined on the activity of the proton. At 25 °C, pH + pOH = 14 for pure water.

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