Difference Between Pure Substance and Homogeneous Mixture

Pure Substance vs Homogeneous Mixture
 

Single elements are hardly stable under natural conditions. They form various combinations among them or with other elements in order to exist. Not only elements, molecules and compounds also tend to mix with a large number of other species in nature. Therefore, we can broadly categorize matter into two categories as pure substances and mixtures. Mixtures can be mainly divided into two, as homogeneous mixtures and heterogeneous mixtures.

Pure Substance

Pure substance cannot be separated into two or more substances by any mechanical or physical method. Therefore, pure substance is homogenous. It has a uniform composition throughout the sample. Further, the properties of it are also uniform throughout the sample. Elements are pure substances. An element is a chemical substance, which consists of only a single type of atoms; hence, they are pure. There are about 118 elements given in the periodic table according to their atomic number. For example, the smallest element is the hydrogen. Silver, gold, and platinum are some of the commonly known precious elements. Elements can be subjected to chemical changes to form various compounds; however, elements cannot be further broken down by simple chemical methods. Compounds are the other type of pure substances. Compounds are made up by two or more different chemical elements. Although there are two or more elements joined when forming a compound, these cannot be separated by any physical means. Rather, they can only be decomposed by chemical means. Therefore, this makes a compound a pure substance.

Homogeneous Mixture

Mixture contains two or more substances, which are not chemically combined. They only have physical interactions. Since they do not have any chemical interactions, in a mixture, the chemical properties of the individual substances retain without change. However, the physical properties like melting point, boiling point can be different in a mixture compared to its individual substances. Therefore, the components of a mixture can be separated using these physical properties. For example, hexane can be separated from a mixture of hexane and water, because hexane boils and evaporates before water does. The amount of substances in a mixture can vary, and these amounts do not have a fixed ratio. Therefore, even two mixtures containing similar types of substances can be different, due to the difference in their mixing ratios. Solutions, alloys, colloids, suspensions are the types of mixtures. Mixtures can be mainly divided into two as homogeneous mixtures and heterogeneous mixtures. A heterogeneous mixture has two or more phases and the components can be individually identified. A homogeneous mixture is uniform; therefore, the individual components cannot be separately identified. When allowed to stay undisturbed, the components of a homogeneous mixture do not settle down. Solutions and colloids are the two main categories of a homogeneous mixture. The components of a solution are mainly of two types, solutes and the solvent. Solvent dissolves the solutes and form a uniform solution. The particles in colloidal solutions are of intermediate size (larger than molecules), compared to particles in solutions. However, they are invisible to the naked eye and cannot be filtered using a filter paper.