What is Measurement of Potential in Potentiometry

Potentiometry is a technique used to characterize and measure the potential of an analyte. The importance of potentiometry lies in its use of characterizing an acid without the use of an indicator. The instrument used to measure the potential during potentiometric titration is known as the potentiometer. This instrument measures the potential difference with respect to the reference potential. A potentiometer consists of electrodes that detect the concentration of ions and use the information to deliver the potential of the sample. 

Potentiometry

Potentiometry, also known as potentiometric titration, is used to determine the potential of an analyte. Also, the amount of analyte is determined by adding titrants of known concentration till the endpoint. 

Here 2 electrodes are used, one being the indicator electrode and the other, the reference electrode. The indicator electrode records the change in potential as a function of the volume of titrant added with a known concentration. The potential difference is calculated between the two electrodes under thermodynamic equilibrium in the presence of current flow through the electrodes. Here the potential of the cell is recorded after the addition of each titrant.

What is Measured in a Potentiometric Measurement?

The technique of potentiometry is used to measure the potential of an analyte. The potentiometric measurement depends on the potential difference between the indicator electrode and the reference electrode used during the procedure. Specialized electrodes, known as ion-selective electrodes, are also used during potentiometry to measure the potential of the electrolytic solution.

Which Instrument is Used to Measure the Potential in Potentiometry?

The instrument used to measure the potential in potentiometry is known as the potentiometer. This instrument measures the potential difference by comparing an unknown voltage with the reference voltage. The precision of the instrument is high as the reference voltage is calibrated accurately.

The Principle used by Potentiometer

The potentiometer works on the principle that potential difference across a segment of wire having an even cross-section under constant current supply is proportional to the length of the wire. This instrument is used to measure the magnitude of unknown potential. 

Working of Potentiometer

To understand the working of a potentiometer, let us consider two batteries connected in a parallel connection through a galvanometer. If the electric potential across both batteries is similar, it results in no net flow of charge. Hence, there is no current, leading to no deflection in the arrow of the galvanometer.

Now, suppose we connect a battery across a resistor with a uniform electric resistance per unit length of the wire. If the rheostat controlling the current by varying resistance is adjusted, there is a voltage drop observed per unit length of the resistor. The galvanometer measures this voltage drop and gives us the potential across the circuit.

Potentiometric Methods

The potentiometry method is based on the potential difference between the two electrodes used. When the electrodes are placed in the electrolytic solution, the addition of a titrant leads to a change in the concentration of ions which causes changes in the potential difference. The reference electrode plays the role of maintaining a stable potential of the solution. The indicator electrode measures this potential difference. The reference electrode has a potential value and remains stable when dipped into the sample solution.

The salt bridge is a divide used during potentiometric titration to avoid the intervention of the analyte solution with the reference solution. Analyte solution is the solution whose potential we must determine. 

The total electric potential or the potential difference is calculated as

E_cell = E_ind – E_ref + E_j.

• Here E_cell is the potential of the whole cell
• E_ind is the potential or electromotive force of the indicator
• E_ref is the potential or electromotive force of the reference electrode
• E_j is the potential at the junction across the salt bridge.

Here the electrical potential is measured and the electrical potential depends on the concentration of the ions in contact with the indicator electrode.

The curve of Potential in volts vs Volume of analyte in ml gives a negative sigmoidal curve on the graph from which the potential of the analyte after the addition of analyte at every level can be measured easily.

Conclusion

Potentiometry, also regarded as potentiometric titration, is a method used to determine the concentration of a solution in chemistry. The instrument used for measurements in potentiometry is known as the potentiometer. The potentiometer consists of a resistive element known as a resistor, a sliding contact to make electrical contact between the parts of the potentiometer and wires. 2 types of potentiometers that are used; one is the rotary potentiometer and the other is the linear potentiometer. The potentiometer is widely applied in audio controllers, televisions, motion controllers, and transducers.