What is the general composition of the laboratory acidity meter structure

The main body of the acidity meter is a precision potentiometer. During the measurement, the composite electrode is inserted into the measured solution, and different electromotive forces are generated due to the different acidity (hydrogen ion concentration) of the measured solution, which is amplified by a DC amplifier, and finally the pH value of the measured solution is indicated by a reading indicator (voltmeter). Potentiometric measurement with an acidometer is the most precise way to measure pH.

The pH meter consists of three components: a reference electrode; a glass electrode whose potential depends on the pH of the surrounding solution; A galvanometer that measures small potential differences in circuits with very high resistance. Thanks to the latest electrode design and solid-state circuit technology, the best PH can now be distinguished.

The basic function of the reference electrode is to maintain a constant potential that serves as a control for measuring various deviation potentials. The silver-silver oxide electrode is currently the most commonly used reference electrode in pH. The function of the glass electrode is to establish a potential difference that responds to changes in the activity of the hydrogen ions of the measured solution.

A galvanic cell is formed by placing a pH-sensitive electrode and a reference electrode in the same solution, and the potential of the cell is the algebraic sum of the potentials of the glass electrode and the reference electrode. E battery = E reference + e glass, if the temperature is constant, the potential of this battery changes with the pH of the solution to be measured, and it is difficult to measure the potential generated by the battery in the acidity meter because the electromotive force is very small and the impedance of the circuit is very large (1 100m); Therefore, the signal must be amplified enough to push a standard millivoltmeter or milliampere meter. The function of the galvanometer is to amplify the potential of the galvanic battery several times, the amplified signal is displayed through the meter, the degree of deflection of the meter pointer indicates the strength of the signal it pushes, in order to use the needs, the dial of the pH ammeter is engraved with the corresponding pH value; A digital pH meter, on the other hand, displays the pH value directly in numbers.

The acidity meter, referred to as pH meter, is a commonly used instrument and equipment, which is composed of three parts: a reference electrode, a glass electrode and an galvanometer. It is widely used in industry, agriculture, scientific research, environmental protection and other fields.

A pH meter, also known as an acidity meter, is generally used to measure the activity of hydrogen ions in a solution.

The principle of basic line pulse:

Ion activity refers to the effective concentration of ions involved in an electrochemical reaction in an electrolyte solution. There is a quantitative relationship between the activity ( ) and the concentration (c) of the Li's Song, and its expression is: =c, where:

for the activity of ions; is the activity coefficient of the ion; c is the concentration of ions. Usually less than 1, the inter-ion interaction tends to zero when the solution is infinitely diluted, and the activity coefficient tends to 1, and the activity is equal to the actual concentration of the solution. Generally, the concentration of H ions in aqueous solution is very small, so the activity of H ions is basically the same as its concentration.

According to the Nernst equation, the ion activity is proportional to the electrode potential, so the relationship curve between the electrode potential and the activity can be established for the solution, and the ion activity can be determined by measuring the potential, so in fact, we calculate the concentration of h ions by measuring the potential.

There are many models of acidity meters, and their structure mainly includes two parts: electric meter and electrode:

a) Electrodes. The main function of the electrode is to convert the acidity and alkalinity of the measured solution into potential value, and the potential of the electrode changes with the change of the H' concentration in the solution. When the actual measurement is carried out, the electrode is immersed in the solution to be measured, and the H' concentration in the solution is converted into a MV-level voltage signal and sent to the electric meter.

The acidity meter is equipped with an indicator electrode and a reference electrode. The indicator electrode refers to the electrode whose electrode potential changes with the concentration of ions on the side, which is a glass electrode. The reference electrode refers to the electrode whose electrode potential remains constant during the measurement process, generally the mercury glutee electrode or the silver-silver chloride electrode.

Nowadays, it is widely used to combine two electrodes. The change in the heart potential of the indicator electrolysis caused by the change in h' concentration causes the change in the electric potential between the indicator electrode and the reference electrode.

1.Reference electrode.

When the temperature and pressure are constant, the electrode potential of the reference electrode is independent of the concentration of the solution 't1 and remains unchanged during the measurement. Calomel electrodes are the most commonly used reference electrodes. The calomel electrode is composed of Jin Shiwei, door mercury (hg2c12) and potassium chloride solution.*h mercury electrode has two glass sleeves, the inner sleeve is sealed with a pin wire, the platinum wire is inserted into the pure mercury small, and the pure mercury f is filled with a paste of calomel and mercury (hg2c12—hg); The outer sleeve is filled with a sufficiently high saturated potassium chloride solution, and the contact between the lower end of the electrode and the solution to be measured is a porous substance such as a welded ceramic core or glass sand core.

Glass electrodes. The pH glass electrode is a common indicator electrode for determining the pH of a solution. The lower end of the electrode is a spherical glass film made of special glass, which is about one thickness and which only h' can enter and exit. The glass ball is equipped with several hydrochloric acid solutions as the internal reference solution, and silver-silver chloride is inserted into the internal reference solution.

It is required that the lead wire of the electrode and the connecting wire are highly insulated, and at the same time, the metal shield is used to connect with the measuring instrument to eliminate the influence of static induction in the surrounding alternating current field.

Mainly probes and displays.

The main ones are pH electrodes and galvanometers.