According to the words of the law of constant composition, any chemically pure compound remains in the same quantitative composition in no way dependent on the method of its production, which is the first time told the world J. Proust scholar in the 1801-1808 biennium.This law has emerged as a result of the dispute the French chemists Proust and Jean K. Berthollet.The first of them believed that the relationship between the elements of the resulting compounds have a permanent nature, the second saw the variability of connections.One hundred years later, around 1912-1913. NSKurnakov established the existence of compounds with the composition of the variable nature, which he called "berthollides."This group is referred crystalline compounds: phosphides, oxides, carbides, and others.The compounds of the composition of a permanent character on the proposal of a scientist, NSKurnakova became known as "daltonides."The law is always valid in respect of gaseous and liquid substances.
the formulated law of definite proportions logically follows that the elements of matter are connected with one another in a strictly limited proportions.In this regard, there is a concept in chemistry equivalent, which translated from Latin means "equal."In a word, the equivalent - a conventional particulate matter that at a certain number of times less than their corresponding formula units.Any equivalent number corresponds to the nature of the reactants, degree and type of preparation of a chemical reaction.It is distinguished because the equivalent of a specific element in a compound - for well-known groups, ions or molecules.In the reactions of the exchange type, for example, the molar mass of the substance is determined by the equivalent stoichiometry of the reaction taking place.
Typically, many of the elements are capable of forming multiple connections between them.Therefore, the equivalent of the element, as well as the molar mass equivalent, may have different values, looking out from the composition of the test compound were identified.However, in such cases, various equivalents of the same element can be correlated with each other as a relatively small integers.For example, a molar equivalent weight of carbon found in the composition of oxide and carbon dioxide, different and is about 3 grams / mole, and 6 g / mol, and the ratio is equal to the value found in the ratio of 1: 2.As a rule, the majority of compounds containing hydrogen molar mass equivalents, equal to one, and oxygen - eight grams per mole.Equivalent to - this quantity of the substance which is enclosed one mole of valence electrons.
There are several methods to experimentally determine how large molar mass equivalent of whatever element:
- direct method.It is based on the data obtained by synthesis of hydrogen and oxygen compounds of the desired element.
- indirect method.It is used instead of hydrogen and oxygen, other elements with a known equivalent.
- displacement method.It involves the removal of hydrogen from the acid solution using a specific metal hinge.
- analytical method.Based on the calculation of the mass of the substance in one of its compounds.
- Electrochemical method uses data electrolysis.
equivalent molar mass is used to perform quantitative calculations during chemical reactions between certain substances.A significant advantage here is that to solve the problem there is no need to use the equation of chemical reaction, which also is difficult to write.It is only necessary to know that the chemicals involved interact, or the substance - is the product of a chemical reaction.
