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Related Concept Videos

Ionic Association01:28

Ionic Association

The ionic association is the association of oppositely charged ions in an electrolyte solution to form ion pairs. Bjerrum defined ion pairs as two oppositely charged ions whose electrostatic attraction exceeds the thermal energy of the system, typically expressed as 2kT. Electrostatic attraction depends on ionic charge, separation distance, and the dielectric constant of the medium. Thermal energy, represented by kT, reflects the tendency of ions to move independently due to molecular motion.
Aqueous Solutions and Heats of Hydration02:42

Aqueous Solutions and Heats of Hydration

Water and other polar molecules are attracted to ions. The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
Intermolecular Forces03:13

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Ions as Acids and Bases02:54

Ions as Acids and Bases

Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Factors Affecting Solubility04:01

Factors Affecting Solubility

Compared with pure water, the solubility of an ionic compound is less in aqueous solutions containing a common ion (one also produced by dissolution of the ionic compound). This is an example of a phenomenon known as the common ion effect, which is a consequence of the law of mass action that may be explained using Le Chȃtelier’s principle. Consider the dissolution of silver iodide:
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...

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Related Experiment Video

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In Situ Characterization of Hydrated Proteins in Water by SALVI and ToF-SIMS
09:48

In Situ Characterization of Hydrated Proteins in Water by SALVI and ToF-SIMS

Published on: February 15, 2016

Sulfate ion patterns water at long distance.

Jeremy T O'Brien1, James S Prell, Matthew F Bush

  • 1Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.

Journal of the American Chemical Society
|June 4, 2010
PubMed
Summary

This study investigates how sulfate ions affect the structure of water at a distance using infrared photodissociation (IRPD) spectroscopy. The researchers analyzed clusters of sulfate ions with up to 80 water molecules and found a specific band in the IRPD spectra when the cluster contained more than 43 water molecules. This band corresponds to free OH groups in outer-shell water molecules, similar to those found at the surface of bulk water. These findings suggest that sulfate ions have a long-range effect on water structure, which may explain their position in the Hofmeister series. The study provides insights into how ions influence water's hydrogen bonding network and could help refine models of ion-specific effects in biological and industrial contexts.

Keywords:
sulfate ion hydrationinfrared spectroscopywater structureHofmeister series

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Sulfate Separation by Selective Crystallization with a Bis-iminoguanidinium Ligand
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Expression of Cementitious Pore Solution and the Analysis of Its Chemical Composition and Resistivity Using X-ray Fluorescence

Published on: September 23, 2018

Area of Science:

  • Physical chemistry of aqueous solutions
  • Spectroscopy in chemical analysis

Background:

The Hofmeister series describes how ions influence the structure of water and solubility of biomolecules. While much is known about ion-specific effects on water structure, the long-range influence of anions like sulfate remains unclear. Prior research has shown that ions can alter hydrogen bonding networks in water, but the exact mechanisms and distances of these effects are still debated. This uncertainty drives the need for detailed spectroscopic studies to map ion-water interactions. Understanding these interactions could refine models of ion-specific behavior in biological and industrial contexts. However, no prior work had resolved the specific range of sulfate's influence on water structure. This gap motivated the use of IRPD spectroscopy to probe sulfate-water clusters. The study aimed to clarify how sulfate affects water molecules beyond the immediate hydration shell. These findings could help distinguish between short- and long-range effects in Hofmeister series phenomena.

Purpose Of The Study:

This study aimed to investigate the long-range effects of sulfate ions on water structure using IRPD spectroscopy. The specific problem addressed is the lack of clarity about the spatial extent of sulfate's influence on water hydrogen bonding. The motivation stems from the Hofmeister series' relevance to biological and industrial applications where ion-specific effects are critical. The authors sought to determine whether sulfate's effect on water extends beyond the first hydration shell. The study focused on sulfate-water clusters with up to 80 water molecules. By analyzing IRPD spectra, the researchers aimed to identify structural changes in outer-shell water molecules. This approach could reveal how sulfate's hydration pattern compares to other anions in the Hofmeister series. The results could help explain sulfate's position in the series and its role in stabilizing or destabilizing biomolecular structures.

Main Methods:

The researchers used infrared photodissociation (IRPD) spectroscopy to study sulfate-water clusters. They analyzed clusters of SO₄²⁻ with up to 80 water molecules. The method involved measuring IRPD spectra to detect vibrational modes of water molecules. The study focused on the OH stretching region of the spectra to identify hydrogen bonding patterns. The clusters were prepared using a supersonic expansion technique to isolate them in the gas phase. The IRPD spectra were recorded using a tunable infrared laser and a mass spectrometer. The researchers compared spectra for clusters with different numbers of water molecules. The presence of a specific band at 3710 cm⁻¹ indicated structural changes in outer-shell water molecules.

Main Results:

The IRPD spectra of sulfate-water clusters showed a band at approximately 3710 cm⁻¹ when the number of water molecules exceeded 43. This band was absent in clusters with 43 or fewer water molecules. The 3710 cm⁻¹ band corresponds to free OH groups in outer-shell water molecules. These free OH groups resemble those found at the surface of bulk water. The appearance of this band suggests that sulfate influences water structure beyond the first hydration shell. The effect becomes significant when the cluster contains more than 43 water molecules. This finding indicates that sulfate has a long-range effect on water structure. The results support the idea that sulfate's Hofmeister behavior is linked to its influence on water's hydrogen bonding network.

Conclusions:

The study's findings suggest that sulfate ions have a long-range effect on water structure. This effect is evident when the number of water molecules in the cluster exceeds 43. The 3710 cm⁻¹ band indicates that outer-shell water molecules exhibit free OH groups. These free OH groups are characteristic of water at the surface of bulk water. The authors propose that this structural change is a key factor in sulfate's Hofmeister behavior. The results support the hypothesis that sulfate's influence extends beyond the immediate hydration shell. The study provides evidence that the Hofmeister series may be influenced by long-range ion-water interactions. These conclusions align with the authors' interpretation of the IRPD spectroscopy data.

The 3710 cm⁻¹ band indicates the presence of free OH groups in outer-shell water molecules, suggesting structural changes in water influenced by sulfate.

The band at 3710 cm⁻¹ appears only when the cluster contains more than 43 water molecules, indicating a threshold for structural changes.

This band corresponds to free OH groups in outer-shell water molecules, which are similar to those at the surface of bulk water.

IRPD spectroscopy detects vibrational modes of water molecules to identify structural changes in sulfate-water clusters.

The long-range effect of sulfate on water structure may explain its position in the Hofmeister series and its influence on biomolecular stability.

The study suggests that sulfate's Hofmeister behavior is linked to its long-range influence on water structure, which could refine models of ion-specific effects.