potentiometric titratorCharacteristics of
The instrument is controlled by computer software or touch screen, with a Chinese operating interface that is easy to understand;
The instrument adopts a modular design, consisting of a volumetric titration device or a coulombic titration device, a control device (which can be replaced by PC titration software), and a measuring device (including potential measurement, conductivity measurement, and permanent stop measurement). It can achieve potential titration, coulombic titration, conductivity titration, and permanent stop titration;
The instrument is controlled by titration software and can perform various operations;
The instrument has functions such as pre titration, preset endpoint titration, blank titration, or manual titration, which can generate titration modes on their own, expanding the scope of instrument use;
The titration system uses materials resistant to perchloric acid corrosion and can perform non-aqueous titration;
potentiometric titratorThe principle of
Potentiometric titration is a method of determining the endpoint of titration by measuring changes in potential during the titration process. Compared with direct potentiometry, potentiometric titration does not require accurate measurement of electrode potential values. Therefore, the influence of temperature and liquid junction potential is not important, and its accuracy is better than direct potentiometry. Conventional titration relies on changes in indicator color to indicate the endpoint of titration. If the solution to be tested has color or turbidity, it is difficult to indicate the endpoint, or suitable indicators cannot be found at all. Potentiometric titration relies on the sudden jump of electrode potential to indicate the endpoint of titration. Before and after reaching the endpoint of titration, the concentration of the analyte in the droplet often changes continuously by n orders of magnitude, causing a sudden jump in potential. The content of the analyte is still calculated by the amount of titrant consumed.
By using different indicator electrodes, potentiometric titration can be used for acid-base titration, redox titration, combined titration, and precipitation titration. During acid-base titration, a pH glass electrode is used as the indicator electrode, while in redox titration, a platinum electrode can be used as the indicator electrode. In titration, if EDTA is used as the titrant, a mercury electrode can be used as the indicator electrode. In precipitation titration, if silver nitrate is used to titrate halide ions, a silver electrode can be used as the indicator electrode. During the titration process, as the titrant is continuously added, the electrode potential E changes continuously. When the electrode potential suddenly jumps, it indicates that the titration has reached the endpoint. It is easier to determine the titration endpoint using a differential curve than a regular titration curve.
If an automatic potentiometric titrator is used, the titration curve can be automatically drawn during the titration process, the titration endpoint can be automatically identified, and the volume can be automatically given, making titration fast and convenient.
When conducting potentiometric titration, a reference electrode and an indicator electrode are inserted into the tested solution to form a working battery. With the addition of titrant, the concentration of the measured ion constantly changes due to chemical reactions, and the potential of the indicator electrode also changes accordingly. A sudden jump in potential occurs near the waiting point. Therefore, measuring the change in electromotive force of the working battery can determine the endpoint of titration.
The basic equipment for potentiometric titration includes a burette, titration cell, indicator electrode, reference electrode, stirrer, and an instrument for measuring electromotive force.
How does potentiometric titration determine the endpoint of titration? The method of determining the curve by drawing the potential.
The potentiometric titration curve is a graphical representation of the electrode potential value (battery electromotive force) E versus the volume of standard solution added V as titration progresses.
According to different methods of plotting, there are three types of potentiometric titration curves: E-V curve, ordinary potentiometric titration curve, and the inflection point e is the equivalent point.
Determination of inflection point: Draw two 45 ° inclined straight lines tangent to the titration curve, and the intersection point between the dividing line and the curve is the inflection point.
Ee is the equivalent point potential.
Ve is the volume of standard solution required to be added at the equivalence point.
The larger the range and slope of the potential jump, the smaller the analysis error.
Curve, linear derivative curve, first-order derivative curve.
The peak point e of the curve is the equivalent point, which needs to be calculated first when plotting
Calculate using the values of E and V that are adjacent twice:
.
=0 is the equivalent point
V1 and V2 in the equation are the calculated values of the values.
