JoVE Logo

Sign In

2.8 : Acid–Base Equilibria: Activity-Based Definition of pH

For an ideal solution, the pH is defined as the negative logarithm of the hydrogen ion concentration. For a non-ideal solution, an accurate measurement of the pH must consider the negative logarithm of the hydrogen ion activity rather than concentration. In such a solution, the pH can be more accurately defined as the negative logarithm of a product of the hydrogen ion concentration and its activity coefficient.

In solutions of very low ionic strength—for example, pure water—the activity coefficient of the hydrogen ion is close to one when the ionic strength of the solution increases due to the addition of an electrolyte that does not donate or accept a proton. This results in a slight decrease in the pH of the solution. In other words, the addition of an electrolyte increases the hydrogen ion activity, or the effective hydrogen ion concentration in the solution, which decreases the pH of the solution.

Tags

Acid base EquilibriaPH DefinitionHydrogen Ion ConcentrationHydrogen Ion ActivityNon ideal SolutionActivity CoefficientIonic StrengthElectrolyte EffectsEffective Hydrogen Ion Concentration

From Chapter 2:

article

Now Playing

2.8 : Acid–Base Equilibria: Activity-Based Definition of pH

Chemical Equilibria

539 Views

article

2.1 : Ionic Strength: Overview

Chemical Equilibria

1.3K Views

article

2.2 : Ionic Strength: Effects on Chemical Equilibria

Chemical Equilibria

1.3K Views

article

2.3 : Thermodynamics: Chemical Potential and Activity

Chemical Equilibria

875 Views

article

2.4 : Thermodynamics: Activity Coefficient

Chemical Equilibria

1.3K Views

article

2.5 : Chemical Equilibria: Redefining Equilibrium Constant

Chemical Equilibria

521 Views

article

2.6 : Factors Affecting Activity Coefficient

Chemical Equilibria

728 Views

article

2.7 : Chemical Equilibria: Systematic Approach to Equilibrium Calculations

Chemical Equilibria

628 Views

article

2.9 : Ladder Diagrams: Acid–Base Equilibria

Chemical Equilibria

445 Views

article

2.10 : Ladder Diagrams: Redox Equilibria

Chemical Equilibria

428 Views

article

2.11 : Ladder Diagrams: Complexation Equilibria

Chemical Equilibria

319 Views

article

2.12 : Solubility Equilibria: Overview

Chemical Equilibria

589 Views

article

2.13 : Solubility Equilibria: Ionic Product of Water

Chemical Equilibria

931 Views

article

2.14 : Complexation Equilibria: Overview

Chemical Equilibria

614 Views

article

2.15 : Complexation Equilibria: The Chelate Effect

Chemical Equilibria

435 Views

See More

JoVE Logo

Privacy

Terms of Use

Policies

Research

Education

ABOUT JoVE

Copyright © 2025 MyJoVE Corporation. All rights reserved