Laboratory Potentiometric Titrator Overview Classification and Working Principle

Potentiometric titrator overview:

Potentiometric titration titration is a method of determining the titration end point by measuring the potential change during titration. Compared with the direct potentiometric method, potentiometric titration does not require accurate measurement of the electrode potential. Therefore, the influence of temperature and liquid junction potential It is not important, and its accuracy is better than direct electrospinning. Ordinary titration is to indicate the endpoint of the titration by changing the color of the indicator. If the solution to be tested has color or turbidity, the indication of the endpoint is more difficult or impossible to find at all. Suitable indicators. 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.

Potentiometric titrator classification:

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 you use the automatic potentiometric titrator, you can automatically draw the titration curve during the titration process, automatically find the end of the titration, automatically give the volume, and the titration is quick and easy.

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 apparatus for potentiometric titration includes a burette, a titration cell, an indicator electrode, a reference electrode, a stirrer, and an instrument for measuring electromotive force.

How does the potentiometric titration determine the end point of the titration? The method of plotting the potential is used 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.