What Is the Law of Definite Proportions?

The law of definite ratio, that is, each compound, whether it is naturally occurring or synthetic, and no matter how it is prepared, the quality of its constituent elements has a certain proportional relationship. This law is called Law of certain ratio. Proposed by Proust in 1799. Putting it another way, every compound has a certain composition, so the law of definite ratio is also called the law of definite composition.

Definite law

Right!

The law of definite ratio, that is, each compound, whether it is naturally occurring or synthetic, and no matter how it is prepared, the quality of its constituent elements has a certain proportional relationship. This law is called Law of certain ratio. Proposed by Proust in 1799. To put it another way, every compound has a certain composition, so the law of definite ratio is also called

English: Law of Definite Composition or Proportion

For example, regardless of method or time and place

Establishment of the law of definite ratio

The law of ratios was proved experimentally by French J.-L. Proust at the turn of the 18th and 19th centuries. He analyzed the minerals collected from all over the world and the same compounds that he prepared in the laboratory. It is proved that there is only one kind of sodium chloride and one kind of calcium sulfate in the world, and the law of ratio is established.

Exception to the law of ratio

C.-L. Betole, a contemporary of Proust, believes that the composition of the compound will change with different preparation conditions or within a certain range with the relative weight of the raw materials used to synthesize the compound Betole also experimentally proved his views, but his views were not accepted by most chemists at the time. After the 20th century, it was found that there are exceptions to the law of ratios. There are some compounds whose composition can be changed in a small range. For example, the composition of brass should be Cu5 · Zn3, which is equivalent to 62% zinc, In fact, the zinc content can be continuously changed in the range of 59% to 67%, which proves that there are indeed compounds with variable composition. They are called non-stoichiometric compounds, also known as betolelite .

The law of definite ratio was initially formed

Since the end of the 17th century, the concept of the law of definite ratio has gradually come into being during the quantitative research of various types of chemical reactions in pharmaceuticals and a series of scientific experiments. Because people have gradually realized that there is a definite weight ratio relationship between reactants and products, each compound has its definite composition.

The law of constant ratio is widely used

In the middle of the 18th century, many analysts consciously used this basic concept and used some metal precipitated compounds as a weighing form in gravimetric analysis. When Clark used a quantitative method to test the acid gas with lime water, he actually confirmed the calcium carbonate fixed composition. Therefore, at the end of the 19th century, the basic concept of the law of definite ratio was accepted and used by many people. But Prost only carried out a more extensive, more systematic and more precise research on this basis, so that the law has a more rigorous scientific experimental basis.

Definite law debate

In 1799, Prost elaborated the law of definite ratio to make it face the world systematically. Prost is a French pharmacist with long research and experimental experience. Based on the results of his experiments, he pointed out that the composition of natural and artificial base copper carbonate is exactly the same. This fact leads to the conclusion that the weight ratio of two or more element-phase compounds into a certain compound cannot be increased or decreased.

However, once this law was proposed by Zeng Rost, it was severely attacked by the then French chemist Betoret. At the time, Betore also published the article "The Law of Chemical Affinity", the main point of which was exactly contrary to the law of definite ratio. He believes that one substance can be combined with another substance with mutual affinity in all proportions. He firmly believes that the relative mass of matter has an important effect on the composition of the compound during the reaction. The core theory is that the composition of a compound is endless, not fixed. The root of this insight is that Betorre pays more attention to the process of chemical change than to the products of change. Although he had the right view, and even foresaw the laws of mass action discovered by physical chemists in the 1960s, this time, Betoret was wrong. To criticize Prost, he took solutions, alloys, glass as examples, and even some metal oxides and salts were basically mixtures, not compounds.

From 1802 to 1808, Prost published a number of papers in response to Betoret's criticism. He acknowledged that several identical elements could produce different compounds. However, it is also pointed out that there are not many types of these compounds, often only two, and each compound has its own fixed composition. And in these several compounds, the compounding ratio is obviously different. He said that the components of the mixture can be physically separated. Therefore, we say that Prost was the first to correctly distinguish between a mixture and a compound. According to Betorre, the composition of a compound varies depending on the physical conditions at which it was formed.

Prost's criticism of this view is the lack of sufficiently accurate quantitative analysis techniques and methods. Like most chemists of this period, the experimental deviation was large, and the analysis was quite accurate until the middle of the 19th century. It turns out that the law of definite ratio has only a small deviation.

Later, in order to verify Prost's hypothesis, Belgian analytical chemist Starr performed extremely precise experiments and obtained extremely accurate data, which confirmed the Prost hypothesis. At this point, the debate over the law of definite ratio lasted for more than 70 years, and finally ended.

The general theory of definite law

For example copper oxide, this compound is composed of oxygen and copper. That is, it is composed of oxygen ions and copper ions, and because the oxygen ions and copper ions have a fixed number of nuclear charges, the ratio is also fixed. The exception is because the number of nuclear charges is sometimes unstable.