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Related Concept Videos

Ionic Association01:28

Ionic Association

216
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.
216
Polyprotic Acids03:38

Polyprotic Acids

25.5K
Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:
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Relative Strengths of Conjugate Acid-Base Pairs02:29

Relative Strengths of Conjugate Acid-Base Pairs

36.8K
Brønsted-Lowry acid-base chemistry is the transfer of protons; thus, logic suggests a relation between the relative strengths of conjugate acid-base pairs. The strength of an acid or base is quantified in its ionization constant, Ka or Kb, which represents the extent of the acid or base ionization reaction. For the conjugate acid-base pair HA / A−, the ionization equilibrium equations and ionization constant expressions are
36.8K
Weak Acid Solutions04:02

Weak Acid Solutions

31.3K
Few compounds act as strong acids. A far greater number of compounds behave as weak acids and only partially react with water, leaving a large majority of dissolved molecules in their original form and generating a relatively small amount of hydronium ions. Weak acids are commonly encountered in nature, being the substances partly responsible for the tangy taste of citrus fruits, the stinging sensation of insect bites, and the unpleasant smells associated with body odor. A familiar example of a...
31.3K
Strong Acid and Base Solutions03:22

Strong Acid and Base Solutions

28.2K
A strong acid is a compound that dissociates completely in an aqueous solution and produces a concentration of hydronium ions equal to the initial concentration of acid. For example, 0.20 M hydrobromic acid will dissociate completely in water and produces 0.20 M of hydronium ions and 0.20 M of bromide ions.
28.2K
Mixtures of Acids01:19

Mixtures of Acids

1.2K
The pH of a solution containing an acid can be determined using its acid dissociation constant and initial concentration. If a solution contains two different acids, then its pH can be determined using one of several methods depending on the relative strength of the acids and their dissociation constants.
In a strong and weak acid mixture, the strong acid dissociates completely and becomes a source of almost all the hydronium ions present in the solution. In contrast, the weak acid shows...
1.2K

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Persistent ion pairing in aqueous hydrochloric acid.

Marcel D Baer1, John L Fulton, Mahalingam Balasubramanian

  • 1Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.

The Journal of Physical Chemistry. B
|May 20, 2014
PubMed
Summary
This summary is machine-generated.

Strong acid solutions contain chloride-hydronium ion pairs, challenging the spectator ion assumption. These ion pairs persist across concentrations, offering new insights into acid dissociation and equilibria.

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Area of Science:

  • Physical Chemistry
  • Solution Chemistry
  • Computational Chemistry

Background:

  • Strong acids like hydrochloric acid are assumed to fully dissociate.
  • Counterions are often treated as passive spectators in acid dissociation models.
  • Previous models did not fully account for specific ion interactions in concentrated solutions.

Purpose of the Study:

  • To investigate the molecular structure of concentrated hydrochloric acid solutions.
  • To determine the role of counterions in acid dissociation.
  • To provide a molecular-level understanding of acid-base equilibria.

Main Methods:

  • Extended X-ray absorption fine structure (EXAFS) measurements.
  • State-of-the-art density functional theory (DFT) simulations.
  • Comparison of experimental data with theoretical models.

Main Results:

  • Evidence for chloride-hydronium (Cl(-)···H3O(+)) contact ion pairs in 2.5 m hydrochloric acid.
  • The persistence of these contact ion pairs across the studied concentration range.
  • Significant structural differences between concentrated solution ion pairs and gas phase clusters.

Conclusions:

  • Counterions in strong acid solutions are not mere spectators.
  • Contact ion pairs play a crucial role in the molecular structure of concentrated electrolytes.
  • This finding necessitates a revised molecular-level description of acid dissociation and acid-base equilibria.