Potentiometric titrator working principle introduced

The titration method is a method of determining the titration end point by measuring the potential change during the titration process. Compared with the direct potentiometric method, the potentiometric titration method does not need to accurately measure the electrode potential value. Therefore, the influence of the temperature and the liquid junction potential is not important. The accuracy is better than the direct electric pull method. Ordinary titration method is based on indicator color change to indicate the titration end point. If the test solution has color or turbidity, the indication of the end point is more difficult, or no suitable indicator can be found at all. . Potentiometric titration is based on a sudden jump in electrode potential to indicate the endpoint of the titration. Before and after the titration reaches the endpoint, the concentration of the ion to be measured in the droplet is often continuously changed by n orders of magnitude, causing a jump in the potential. The content of the measured component is still calculated by the amount of titrant consumed.

Using different indicator electrodes, potentiometric titration can be performed for acid-base titration, redox titration, complex titration and precipitation titration. The pH glass electrode was used as the indicator electrode in the acid-base titration. In the oxidation-reduction titration, the platinum electrode was used as the indicator electrode. In the complex titration, if EDTA is used as titrant, the mercury electrode can be used as the indicator electrode. In the precipitation titration, if silver nitrate is used to titrate the halide ion, the silver electrode can be used as the indicator electrode. During the titration process, with the constant addition of titrant, the potential E of the electrode continuously changes, and when the potential of the electrode suddenly jumps, the titration reaches the end point. The end point of the titration can be determined more easily with a differential curve than with a normal titration curve.

If a potentiometric titrator is used, the titration curve can be drawn automatically during the titration process, the titration end point can be automatically found out, the volume can be given automatically, and the titration can be performed quickly and easily.

When potentiometric titration is performed, a reference electrode is inserted in the test solution, and an indicator electrode constitutes a working battery. With the addition of the titrant, due to a chemical reaction, the measured ion concentration constantly changes and the potential of the indicator electrode also changes accordingly. Potential jumps occur near the point of equalization. Therefore, the change of the electromotive force of the working battery can be measured to determine the titration end point.

The basic equipment for potentiometric titration includes a burette, a titration cell, an indicator electrode, a reference electrode, a stirrer, and a potentiometric titrator.

How does the potentiometric titration determine the endpoint of the titration? Use plot potentials to determine the curve.

The potentiometric titration curve is a graph in which the electrode potential value (cell electromotive force) E is plotted against the added volume V of the standard solution as the titration progresses.

According to the method of drawing, the potentiometric titration curve has three types, EV curve, ordinary potentiometric titration curve, and the inflection point e is the equal point.

Determination of the inflection point: Make two straight lines with 45° tangent to the titration curve, and the intersection point between the bisector and the curve is the inflection point.

Ee is equal point potential.

Ve is the volume of the standard solution to be added at the equal point.

The larger the potential jump range and slope, the smaller the analysis error.

Curve, first derivative curve, first derivative curve.

The e-point of the peak of the curve is the equivalent point, which must be calculated first.

Use the E,V values ​​that are two adjacent values ​​to find:. When =0, V1 and V2 in the equal point formula are the calculated values.