Name: how ionic strength changes activity coefficient
Uploaded: 2024-04-04T10:51:15.000Z
Duration: 1 min 17 s
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IPC.8.B

Factors Affecting Activity Coefficient

The activity coefficient of an ion depends on the ionic strength of the solution.
As indicated by the Debye&#8211;H&#252;ckel theory, when the ionic strength approaches zero, the activity coefficient approaches unity.
As the ionic strength increases from 0 to 0.1 moles per liter, the activity coefficient value decreases.
However, with an increase in ionic strength above 0.1 moles per liter, the activity coefficient may increase.
The influence of ionic strength on the activity coefficient is associated with the charge of the ion, which also directly influences the activity coefficient.
With an increased charge on the ion, the decrease in the activity coefficient is even more pronounced.
For a particular ionic strength, ions with the same charges have approximately the same activity coefficients.
Another significant factor affecting the activity coefficient of an ion is the ion size parameter&#8212;the effective diameter of the hydrated ion.
Smaller ions with a high charge have larger effective diameters and deviate less from ideality than similarly charged ions with smaller diameters do.

factoren die de activiteitscoëfficiënt beïnvloeden

De uitgebreide vergelijking van Debye-Hückel geeft aan dat de activiteitscoëfficiënt van een ion in een waterige oplossing bij 25°C afhangt van drie gedeeltelijk onderling afhankelijke eigenschappen: de ionsterkte van de oplossing, de lading van het ion en de ionengrootte.

De activiteitscoëfficiënt waarde voor een ion ligt dicht bij één wanneer de oplossing een ionsterkte van bijna nul heeft, dat wil zeggen wanneer de oplossing een bijna ideaal gedrag vertoont. Naarmate de ionsterkte van de oplossing toeneemt van 0 tot 0,1 mol/l, wordt een afname van de activiteitscoëfficiënt waarde waargenomen.

Oplossingen met een ionsterkte boven 0,1 mol/L worden niet goed weergegeven door de Debye-Hückel-vergelijking. In dergelijke oplossingen kan de activiteitscoëfficiënt van een ion groter zijn dan één. De ionsterkte van de oplossing hangt nauw samen met de lading van de ionen die in de oplossing aanwezig zijn, waardoor hun activiteitscoëfficiënt wordt beïnvloed. Voor een bepaalde ionsterkte hebben ionen met minder lading hogere activiteitscoëfficiënt waarden dan ionen met een hogere lading. Met andere woorden, de afwijking van de idealiteit is meer uitgesproken voor meervoudig geladen ionen dan voor enkelvoudig geladen ionen.

Ionen met vergelijkbare ladingen hebben vaak vergelijkbare activiteitscoëfficiënten. De dominante factor in de coëfficiëntverschillen is de parameter iongrootte. De ionengrootte beschrijft de effectieve diameter van een gehydrateerd ion, en zelfs ionen met vergelijkbare ladingen hebben de neiging een verschillende mate van hydratatie te hebben en daarom verschillende ionengroottes. Ionen met vergelijkbare ladingen kunnen in verschillende mate worden gehydrateerd, wat resulteert in verschillende effectieve diameters. Deze diameters staan ​​bekend als de iongrootte parameters. Ionen met kleinere ionengrootteparameters wijken meer af van de idealiteit, wat resulteert in een lagere activiteitscoëfficiënt dan die met grotere ionengrootteparameters maar dezelfde lading.

The activity coefficient of an ion depends on the ionic strength of the solution.
As indicated by the Debye&#8211;H&#252;ckel theory, when the ionic ...

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how ionic strength changes activity coefficient

The activity coefficient of an ion in water depends on ionic strength, ion charge, and ion size. The extended Debye-Hückel equation describes these effects for aqueous solutions at 25°C. These three factors are partly linked, so changes in one can influence the others.

When a solution has almost zero ionic strength, the activity coefficient is close to one. That means the solution behaves almost ideally. As ionic strength rises from 0 to 0.1 mol/L, the activity coefficient usually drops. Solutions with ionic strength above 0.1 mol/L are not well described by the Debye-Hückel equation, and the activity coefficient may even become greater than one.

Ion charge also affects the activity coefficient because ionic strength depends on the ions present in the solution. At the same ionic strength, ions with lower charge usually have higher activity coefficient values than ions with higher charge. This means multiply charged ions show a larger departure from ideal behavior than singly charged ions. Ions with similar charges often have similar activity coefficients.

Ion size is the main reason that activity coefficients can still differ for ions with the same charge. Ion size refers to the effective diameter of a hydrated ion, which depends on how much water surrounds it. Ions with similar charges can be hydrated to different extents, so they can have different ion size parameters. Smaller ion size parameters lead to greater deviation from ideal behavior and a lower activity coefficient than larger ion size parameters for ions with the same charge.

How Ionic Strength Changes Activity Coefficient

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Activity coefficient in ionic solutions describes how much a species behaves like its measured concentration. Activity is the effective concentration of a solute in solution. It equals the molar concentration multiplied by the activity coefficient, which is a unitless number. The activity coefficient depends on the total ionic strength of the solution. It shows how far a solution is from ideal behavior. When ionic strength is very low, the activity coefficient of an ionic species is close to...

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Salt effect changes how a sparingly soluble salt dissolves when an inert salt is added. The size of this effect depends on the ionic strength of the solution. Ionic strength reflects how strongly the ions in the solution interact. In solution, the activity of a species is the product of its concentration and its activity coefficient. A redefined equilibrium constant must account for these activity effects when the ionic strength is moderately high. This form is also called the thermodynamic...

factors affecting activity coefficient

The activity coefficient of an ion in water depends on ionic strength, ion charge, and ion size. The extended Debye-Hückel equation describes these effects for aqueous solutions at 25°C. These three factors are partly linked, so changes in one can influence the others. When a solution has almost zero ionic strength, the activity coefficient is close to one. That means the solution behaves almost ideally. As ionic strength rises from 0 to 0.1 mol/L, the activity coefficient usually drops.

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key terms and concepts

Learn how ionic strength, ion charge, and ion size affect activity coefficients in aqueous solutions using the extended Debye-Hückel equation.

How Ionic Strength Changes Activity Coefficient | JoVE K12

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How Ionic Strength Changes Activity Coefficient

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