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Related Concept Videos

Water: A Bronsted-Lowry Acid and Base02:30

Water: A Bronsted-Lowry Acid and Base

The reaction between a Brønsted-Lowry acid and water is called acid ionization. For example, when hydrogen fluoride dissolves in water and ionizes, protons are transferred from hydrogen fluoride molecules to water molecules, yielding hydronium ions and fluoride ions:
Leveling Effect and Non-Aqueous Acid-Base Solutions02:11

Leveling Effect and Non-Aqueous Acid-Base Solutions

This lesson defines the leveling effect in acidic and basic solutions and its role in aqueous and non-aqueous solutions. It is essential to understand the competing nature of various species in a chemical system.
The Leveling Effect of a Solvent
A generic acid (HA) reacts with the generic base (B-) to yield the corresponding conjugate base (A-) and conjugate acid (HB):
Solubility Equilibria: Ionic Product of Water01:16

Solubility Equilibria: Ionic Product of Water

Pure water is a weak electrolyte; only a small amount ionizes into hydrogen and hydroxide ions. At any given temperature, the concentration of undissociated water is almost constant, so the ionic product of water is the product of the hydrogen and hydroxide ion concentrations, denoted as Kw. The square root of Kw gives the individual ion concentrations.
The ionic product of water varies with temperature, and its value is 1.0 x 10−14 at standard experimental conditions. Per Le Chatelier's...
Surface Tension of Fluid01:22

Surface Tension of Fluid

Surface tension is a fundamental property of fluids, occurring at the boundary between a liquid and a gas or between two immiscible liquids. This phenomenon arises from the cohesive forces between molecules at the fluid's surface, creating an effect similar to a stretched elastic membrane. Inside each fluid, molecules are equally attracted in all directions by neighboring molecules, but surface molecules experience a net inward force, resulting in surface tension.
Surface tension varies with...
Surface Tension, Capillary Action, and Viscosity02:57

Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
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Surface Tension and Surface Energy

When a paint brush is immersed in water, the bristles wave freely inside the water. When it is taken out, the bristles stick together. The reason behind this effect is surface tension.
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Updated: Jun 25, 2026

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices
09:31

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

Published on: March 27, 2019

The surface of neat water is basic.

James K Beattie1, Alex M Djerdjev, Gregory G Warr

  • 1School of Chemistry, University of Sydney, NSW, 2006, Australia. j.beattie@chem.usyd.edu.au

Faraday Discussions
|February 21, 2009
PubMed
Summary

Contrary to theory, experimental evidence shows water surfaces are negatively charged due to hydroxide adsorption, not proton adsorption. This impacts understanding of water interfaces and emulsion formation.

Area of Science:

  • Physical Chemistry
  • Surface Science
  • Colloid Science

Background:

  • Theoretical models suggest water surfaces are acidic due to hydronium ion adsorption.
  • Experimental data, including charged air bubbles and oil drops, contradict these theoretical conclusions.
  • Zeta potential measurements on inert surfaces indicate a negative surface charge in water.

Purpose of the Study:

  • To reconcile theoretical predictions with experimental observations of water surface charge.
  • To investigate the behavior of water at hydrophobic interfaces.
  • To understand the mechanism of emulsion formation in surfactant-free systems.

Main Methods:

  • Analysis of existing experimental data on zeta potential and surface charge.
  • Comparison of theoretical hydronium ion adsorption with experimental hydroxide ion adsorption.

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  • Observation of emulsion formation from inert oil and water without salts or surfactants.

    • Main Results:

    • Water surfaces at inert hydrophobic interfaces exhibit preferential hydroxide ion adsorption, resulting in a negative surface charge.
    • The isoelectric point, observed between pH 2-4, implies a strong preference for hydroxide over protons.
    • Emulsification of oil in water, even without surfactants, is driven by hydroxide adsorption and increased water autolysis.

    Conclusions:

    • Experimental evidence strongly supports a negatively charged water surface at hydrophobic interfaces due to hydroxide adsorption.
    • Theoretical models predicting acidic water surfaces are inconsistent with observed phenomena.
    • Hydroxide adsorption at interfaces plays a crucial role in stabilizing surfactant-free emulsions.