A reference substance is a substance used in analytical chemistry to directly prepare a standard solution or to calibrate the concentration of a manipulated solution in titration analysis. The definition of reference substances is becoming more and more accurate, the classification is clear, and it has an important role in many fields. So what are the conditions that the reference substance has to meet to determine the concentration of the standard solution? Next, Bolinda Xiaobian to introduce it to you.

The reference substance for calibration of the concentration of the standard solution must meet the following conditions:

1, the composition of the reference material must be fully consistent with the chemical formula, the substance containing crystal water, the content of crystal water should also be consistent with its chemical formula.

2, the reference material should have a certain stability, does not absorb water and carbon dioxide in the air, is oxidized by the air, can be maintained for a long time, the reference contains crystal water, each use of 1 month before recrystallization must be carried out.

3, the reference material must be soluble in water and easy to refine and dry.

4, the reaction of the reference substance with the titrated solution must be rapid, and comply with the reaction rules of the amount of such substances.

5, the reference material should have a large molar mass of the basic unit in order to reduce the relative error of weighing.

6, the reference material should have a high purity, usually the impurity content should not exceed 0.01%-0.02%; GR(Superior pure) or AR(analytical pure) reagents are generally used; When the new reference reagent is used, it must be compared with the reference substance previously used.

The above content is to calibrate the standard solution concentration of the reference material conditions are introduced, commonly used reference materials are silver, copper, zinc, aluminum, iron and other pure metals and oxides, potassium dichromate, potassium carbonate, sodium chloride, potassium hydrogen phthalate, oxalic acid, borax and other pure compounds. Since the 1950s, many people have considered that the amount of electricity (Coulomb number) can be accurately measured, and it is recommended to use coulomb as a practical reference substance, instead of some pure chemical reagents.