Potentiometric Titration: Principle, Methods and Types

Potentiometric titration is similar to direct titration except that instead of using an indicator reagent, an electrode is utilized as an indicator. A cell with a reference electrode, salt bridge, analyte, and indicator electrode is used in potentiometric titrations. The electrolyte solution is typically utilized as an analyte. As reference electrodes, hydrogen electrodes, silver chloride electrodes, and calomel electrodes are commonly used. Glass and metal ion electrodes are commonly used as indicator electrodes. Let’s have a closer look at the topic and discuss some important questions.

Keywords: Potentiometric titration, titration, Electrodes, Hydrogen, Acid-base titration, redox titration, complexometric titration, precipitation titration, silver chloride, salt bridge

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What is Potentiometric Titration?

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Potentiometric titration is the technique for determining the quantity of a specific test substance by adding titrant in small increments until the entire test substance reacts. The potential difference between the two electrodes (the reference and indicator electrodes) is measured after the titration process in conditions when the thermodynamic equilibrium is maintained and the current running through the electrodes does not affect it.

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Principle of Potentiometric Titration

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A laboratory method for determining the concentration of a particular analyte is potentiometric titration. It's used to figure out the characteristics of acids. No chemical indicator is used in this procedure. Instead, the electric potential is measured across the substance.

The addition of the titrant or a change in the concentration of ions displays the potential difference between two electrodes when the pair of electrodes is placed in the sample solution or analyte.

Reference electrodes and indication electrodes are the two electrodes. When an electrode is dipped into a sample solution, the reference electrode maintains its potential and remains stable. An indicator electrode is one that reacts to changes in the potential of an analyte solution. To keep the analyte from interfering with the reference electrode, a salt bridge is utilized.

The electromotive force, often known as the total potential difference, can be computed using the formula:

Where,

E_cell is the total electromotive force of the cell.

E_ind = the indicator electrode's electromotive force

E_ref = reference electrode electromotive force

E_j = electromotive force at the salt bridge's junction

Also Read: Electron Hole or Electron Vacancy

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Method followed in Potentiometric Titration

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The potential of an indicator electrode with respect to a reference electrode is measured as a function of titrant volume in potentiometric titration. We measure and record the cell potential (in millivolts or pH) after each addition of titrant in this titration. As we get closer to the end, we start adding titrants in very small amounts. Plotting a graph between cell potential and titrant volume is the most basic and widely used method of endpoint detection in potentiometric titration. The endpoint is approximated visually as the midway of the rapidly rising portion of the graph or curve.

Now if a graph is plotted with the Potential difference on the Y-axis and the volume on the X-axis, the graph will be as shown below: 

The electric potential of the cell is proportional to the concentration of ions in contact with the indicator electrode, as shown in the graph. As a result, the Ecell is measured after each titrant addition.

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Types of Potentiometric Titration

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Acid-base titration, redox titration, complexometric titration, and precipitation titration are the four types of titration that fall under the category of potentiometric titration. Below is a brief summary of each of these titration methods.

Acid-Base Titration: This type of potentiometric titration is used to determine the concentration of a given acid/base by neutralizing it precisely with a known-concentration standard solution of base/acid.

Redox Titration: This type of potentiometric titration involves a redox reaction between the analyte and the titrant. The treatment of an iodine solution with a reducing agent to produce the iodide ion is an example of this type of titration (a starch indicator is used to get the endpoint).

Chelatometry: This method of titration is also known as complexometric titration. A coloured complex is created in this procedure, signifying the titration's end point. This approach is used to identify a metal ion combination in a solution.

Precipitation Titration: This method of titration involves forming an insoluble precipitate from an interaction between the analyte and the titrant. When the addition of the titrant no longer generates a precipitate, the titration is complete.

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Application of Potentiometric Titration

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• It is used in clinical chemistry for the analysis of metals. 
• It is used for the analysis of cyanide, ammonia etc., in water or wastewater. 
• It is used in agriculture for the detection of different elements in soils, fertilizers etc. 
• It is used in detergent manufacturing, food processing etc.

Other applications of potentiometric titrations across various industries are as follows:

Chemistry in medicine / Clinic

Because analytes in complex matrices are selective for ion-selective electrodes in clinical chemistry, they are useful sensors. Sodium, potassium, calcium, hydrogen, and chlorine, as well as dissolved gasses like CO₂, are frequently utilized as analytes.

Environmental chemistry

Environmental chemistry is used to determine the concentrations of CN^-, NO₃, F₃, and NH₃ in water and wastewater.

Titrations through potentiometry

A potentiometric acid-base titration is performed to determine the equivalence point. Titration can be done in both aqueous and non-aqueous solvents for chemical reactions such precipitation, acids, bases, redox processes, complexations, and other chemical reactions.

Agriculture

NO₃, NH₄, I, Ca, K, and CN are all components found in soils, plant materials, feed, and fertilizers used in agriculture.

Production of detergent

The effects of calcium, barium, and fluorine in detergent production are being investigated.

Also Check: Imperfections in Solids

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Things to Remember

• Potentiometric titration is the technique for determining the quantity of a specific test substance by adding titrant in small increments until the entire test substance reacts. 
• The electromotive force, often known as the total potential difference, can be computed using the formula: E_ind – E_ref + E_j = E_cell
• The potential of an indicator electrode with respect to a reference electrode is measured as a function of titrant volume in potentiometric titration. 
• We measure and record the cell potential (in millivolts or pH) after each addition of titrant in this titration. 
• It is used in clinical chemistry for the analysis of metals. 
• It is used for the analysis of cyanide, ammonia etc., in water or wastewater. 
• It is used in agriculture for the detection of different elements in soils, fertilizers etc. 

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