Definition of Composition (Chemistry)

Chemical composition refers to the relative proportions in which each element that is part of a substance, compound or material is found. This can change when chemical changes occur or a certain amount of an element is subtracted or added, changing the proportions of the compound.

The fact of designating the chemical composition of any substance speaks of its identity, which which is fundamental for the characterization and understanding of the behavior of different materials. The chemical composition can be represented in different ways, among the most used are: chemical formulas and percentage composition.

Chemical formulas, percentage composition and examples for both models

Chemical elements are the blocks that make up all the substances we know; they are represented by chemical symbols that differentiate them from each other. For example, C for carbon, H for hydrogen, and O for oxygen. One way to represent the chemical composition of a compound is through chemical formulas, and among these the most used is the molecular formula, which uses the symbol of each element present in the compound, followed by a subscript number that indicates the number of atoms of the element that make up the compound. substance. For example, H

₂Or, the molecular formula of water indicates that the chemical composition of this substance is two hydrogen atoms and one oxygen atom, per molecule.

The percentage composition of a substance is the proportion by mass that each element in the compound represents, expressed in percentage units. It is calculated by dividing the mass of each element by the total mass and multiplying by 100%. The calculation of the percentage composition of a compound makes use of the atomic masses reported in the periodic table, corresponding to each of the elements.

For example, if you want to know the percentage composition of water, you must first calculate the molar mass, for this you add the atomic masses of each element, in this case hydrogen and oxygen, multiplied by the number of atoms that each one provides, for hydrogen: H= (1g/mol)(2 atoms)= 2g/mol, and for oxygen: O= (16 g/mol)(1 atom)= 16 g/mol, adding both quantities: 2 g/mol +16 g/mol= 18 g/mol, this will be taken as mass total. Now, divide the mass of each element by the total mass and multiply by 100%, for hydrogen: (2 g/mol/18 g/mol)(100%)= 11%, (16 g/mol/18 g/mol)(100%)= 89%. As a result, the percentage composition of water would be 11% hydrogen, 89% oxygen. This representation of the chemical composition is especially useful for mixtures, which are entities of two or more compounds. combined, here the percentage composition is used to determine the concentration of each compound in the mixture and predict its behavior.

There are different methods to determine the chemical composition of a substance. Among them, analytical techniques such as infrared spectroscopy, mass spectrometry and magnetic resonance nuclear, can identify specific molecules in a substance, by comparing the patterns and spectra they generate against standards. Chromatography is another widely used technique as it separates the components of a mixture based on their differences in solubility, in order to know the components in an unknown mixture. Elemental chemical analysis encompasses techniques such as absorption spectroscopy, which is based on wavelengths that absorbs a certain element and based on recorded spectra it is possible to know which element is present in the substance. Certain microscopy techniques, such as transmission electron microscopy, can also help identify particles present in a sample. In addition, there are quantitative techniques that allow determining the chemical composition of a substance through reactions that reveal the identity of certain molecules, such as acid-base, oxidation-reduction, and precipitation.

Applications

Understanding the chemical composition of substances is essential in many applications, not only in chemistry, but in materials engineering, environmental science, biology, condensed matter physics and medicine, among other. In industrial processes, for example, it is of utmost importance to know the exact chemical composition of the reagents that are used as raw materials to produce certain valuable products will result, this will ensure total control of their quality and purity, as well as in terms of safety in the different stages of prosecution.

Speaking a little about the relevance of chemical composition in the area of ​​health, when it comes to analysis for the diagnosis of certain diseases, the analytical methods are determinants, since by knowing what the chemical composition of the biological samples is, it is possible to know their origin or identify their origin, in addition, for the development of drugs and research in this area for their formulation, it is very important to have quality control that analyzes the chemical composition of the products that go to the market. market.