Chapter 34: Problem 1

Test your understanding of the circumstances under which ion-selective electrodes can be used. List the three main assumptions underlying the measurement of ion concentration using an ion-selective electrode.

Short Answer

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The three main assumptions when using an ion-selective electrode to measure ion concentration are: 1) The electrode is selective to a specific ion in a mixture; 2) There's a linear response to changes in the logarithm of ion activity; 3) The ion activity coefficients remain constant at all concentrations.

Step by step solution

Understanding Ion-Selective Electrodes

An ion-selective electrode (ISE) is a sensor that converts the activity of a specific ion dissolved in a solution into an electrical potential, which can be measured by a voltmeter or pH meter. The main principles underlying the usage of ISE include the Nernst equation which describes the voltage developed by the electrode as a function of ion concentration.

Unveiling the Assumption 1

The first main assumption is that the electrode responds selectively to a specific ion amidst a mixture of different ions. This means that the electrode shows a great affinity for the designated ion and its effect is mainly due to this ion, minimizing interferences from other ions present in the same solution.

Unveiling the Assumption 2

The second main assumption underpinning the use of ISEs is the linear response of the electrode to changes in the logarithm of activity (or the concentration) of the target ion, as described by the Nernst equation. Therefore, changes in electrode potential can be directly used to determine the ion's activity.

Unveiling the Assumption 3

The third main assumption is that the ion activity coefficients are constant throughout all the concentrations. This is mainly valid for solutions of low ionic strength and relies on the assumption that the relationship between ion activity and concentration is straightforward, disregarding potential changes due to ionic interactions.

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Test your understanding of the circumstances under which ion-selective electrodes can be used. List the three main assumptions underlying the measurement of ion concentration using an ion-selective electrode.

Short Answer

Step by step solution

Understanding Ion-Selective Electrodes

Unveiling the Assumption 1

Unveiling the Assumption 2

Unveiling the Assumption 3

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