What Is Substance Over Form?

The specific references to the concept of "substance" vary according to the discipline [1]. In chemistry, substance refers to any organic or inorganic substance with a specific molecular identity, including: (1) any substance that is wholly or partly produced as a result of a chemical reaction or any naturally occurring substance; (2) any element or Non-combined atomic groups. Chemical substances include elements, compounds (including additives, impurities), by-products, reaction intermediates and polymers. It does not include mixtures, products (agents), or articles. Molecules can exist independently and are the smallest particles that maintain the chemical properties of a substance. Atoms are the smallest particles in chemical changes. In chemical reactions, atoms recombine into new substances. Atoms combine to form molecules. Ions are charged atoms or groups of atoms.

1. Naturally Occurring Chemical Substance: Any

Chemical substances are the material bearers of chemical movements, as well as the material objects of chemical scientific research. Although this kind of substance object is only represented by substance molecules from the perspective of chemical objects, it has various forms from the perspective of chemical content and involves many substances. Therefore, it is very important to study the classification of chemical substances.

According to the continuous and discontinuous (discrete) forms of matter, chemical substances can first be divided into continuous macroscopic substances, such as various elements,

There are six forms of matter: solid, liquid, gaseous, plasma, Bose-Einstein condensate, and fermion condensate. Solid matter has shape and volume, and their molecules are tightly bound together. Liquid substances also have a volume but no shape

Reference substance

The praimary standard is a substance used in analytical chemistry to directly prepare a standard solution or to calibrate the concentration of an operating solution in a titration analysis. The definition of reference materials is becoming more and more accurate, and the classification is clear, which plays an important role in many fields.

According to the ISO guidelines, the definitions of reference materials and certified reference materials are as follows:

Reference material (RM) A material or substance that has one or more characteristic values that are sufficiently uniform and well-defined to calibrate the measurement device, evaluate the measurement method, or assign a value to the material.

Certified Reference Material (CRM) A certified reference material with one or more characteristic values determined using a procedure that establishes traceability, so that it can be traced back to an accurate representation of the characteristic value. The unit of measurement. Each characteristic value given on the certificate is accompanied by an uncertainty of a given confidence level.

For RM or CRM, there are different titles in different industries and fields in China. Metrologists usually refer to them as "standard materials" and adopt the definitions consistent with the above ISO Guide-30 [4]; standardizers are more accustomed to calling them "standard samples" (referred to as "standard samples" ), And the following definitions are given in GB / T15000.2-1994 [5]: Standard sample (RM) is one or more chemical, physical, biological, engineering technology with sufficient uniformity A batch of samples with technical or performance characteristics such as sensory or sensory, which have been technically identified and accompanied by a certificate of performance data. Certified Standard Sample (CRM) A standard sample that has one or more performance characteristics, has been technically identified, is accompanied by a certificate describing the performance characteristics, and has been approved by the National Standardization Administration.

From the above definitions, they have both the characteristics of metrology and the connotation of standardization. In terms of metallurgy, non-ferrous metals and other industries, there is no essential difference between the two, and their English descriptions are also the same (RM, CRM); for developers, their development procedures are the same and their internal quality requirements are the same For users, the effect is the same or similar. The only differences are the management agencies and application procedures, and the emphasis is slightly different.

Reference substance requirements

It is a high-purity chemically stable substance whose composition is highly consistent with its chemical formula (such as first-grade products or reagents with higher purity than first-grade products).

The reference substance should meet the following requirements: The composition strictly conforms to its chemical formula. If it contains crystal water, the content of crystal water should also be consistent with the chemical formula; The purity is high enough, the main component content is above 99.9%, and the impurities do not affect the accuracy of the titration reaction. Stable in nature, for example, it is not easy to absorb water in the air, carbon dioxide and not easily oxidized by oxygen in the air. When participating in the reaction, the reaction is performed quantitatively according to the reaction formula, and no side reaction occurs. It is better to have a larger molar mass. When preparing a standard solution, a larger amount can be weighed to reduce the relative error of weighing.

Common reference materials and classifications

Commonly used reference materials are pure metals such as silver, copper, zinc, aluminum, and iron, and pure compounds such as potassium dichromate, potassium carbonate, sodium chloride, potassium hydrogen phthalate, oxalic acid, and borax. After the 1950s, many people considered that the amount of electricity (Coulomb number) can be accurately measured, and suggested that Coulomb be used as a practical reference substance instead of some pure chemical reagents.

Generally, reference materials can be divided into three categories:

1. Chemical composition standard substances, such as metals, chemical reagents, etc.

2, physical and chemical properties of standard materials, such as ion activity, viscosity standards, etc.

3. Engineering technical reference materials, such as rubber, audio standards, etc.

According to the form, standard materials can be divided into standard solutions, standard gases, and solid standard materials. ^[2]