Difference Between Indicator Electrode and Reference Electrode

The key difference between indicator electrode and reference electrode is that indicator electrode responds to changes in the activity of the analyte, whereas reference electrode does not respond to changes, and its response is stable.

Indicator electrode and reference electrode are two important components in potentiometric titrations. These are essential to make a potential measurement. Here, one electrode changes according to the changes in the analyte (indicator electrode) whereas the other electrode stays stable with a fixed response (reference electrode).

CONTENTS

1. Overview and Key Difference
2. What is Indicator Electrode 
3. What is Reference Electrode
4. Side by Side Comparison – Indicator Electrode vs Reference Electrode in Tabular Form
5. Summary

What is Indicator Electrode?

Indicator electrode is one of the two electrodes in which the response changes according to the changes in the analyte. There are many types of indicator electrodes we can use to determine the endpoint of potentiometric titrations. Moreover, some examples include glass electrode, metal ion indicator electrode, etc. We denote this electrode as IE. This electrode contains a membrane that is sensitive to the activity of the analyte. Therefore, the potential of IE depends on the concentration of the analyte. Here, the analyte enters the electrode membrane, which causes a change in membrane potential (this is due to the modification of electrochemical properties).

Different types of indicator electrodes are as follows:

• Glass membrane IE
• Crystal membrane IE
• Polymer membrane IE

What is Reference Electrode?

Reference electrode is one of the two electrodes we use in potentiometric analysis as the fixed and stable electrode. Furthermore, it has a stable and well-known electrode potential. In order to obtain this characteristic property, we have to employ a redox system with constant concentrations of each participant of the redox reaction (simply, make a buffered system). Moreover, we can denote this electrode as RE.

Some common examples include:

• Saturated calomel electrode
• Silver/silver chloride electrode
• Standard hydrogen electrode
• pH electrode

What is the Difference Between Indicator Electrode and Reference Electrode?

We can denote the indicator electrode as IE and the reference electrode as RE. The key difference between indicator electrode and reference electrode is that indicator electrode responds to changes in the activity of the analyte, whereas reference electrode does not respond to changes, and its response is stable.

Furthermore, the electrode potential of IE is changeable, but for RE it is a fixed and well-known value. So, this is another difference between indicator electrode and reference electrode. Some examples for IE include glass electrode, metal ion indicator electrode, etc. while examples of RE include saturated calomel electrode, silver/silver chloride electrode, standard hydrogen electrode and pH electrode.

Summary – Indicator Electrode vs Reference Electrode

Indicator electrode has a changeable electrode potential, but reference electrode has a fixed potential. Therefore, the key difference between indicator electrode and reference electrode is that indicator electrode responds to changes in the activity of the analyte, whereas reference electrode does not response to changes, and its response is stable.

Reference:

1. “Reference Electrodes.” Chemistry LibreTexts, Libretexts, 5 June 2019, Available here.