Mixture Separation

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AP ChemName___________________________________

States of Matter: Analysis of an Ocean Beach Mixture

Objective:
To understand how matter is classified and how these classifications are related by analyzing the properties of several chemical systems.

Introduction:
Scientists often need to separate one substance from another. For example, raw iron ore (Fe2O3, for example) contains large amounts of silica (SiO2) and other materials. A chemist’s job is to separate the substances in order to obtain pure iron. Consider the mixture of Fe2O3 and SiO2 which represents a heterogenous mixture. The sand must be removed by physical means. Next, the iron must be separated from the oxygen in the Fe2O3 by means of a chemical reaction.

Pharmaceutical companies also pay strict attention to the separation of compounds. For example, impurities that are harmful if ingested must be removed from all medicines. Think of the consequences of obtaining impure medications. The term purify means to isolate a pure substance.

Classes of Matter. Heterogeneous and homogenous mixtures are the two main classes of bulk matter. A heterogenous mixture is matter in which two or more phases or substances are discernible. A heterogeneous mixture is nonuniform such as oil in water or salt in pepper. A homogenous mixture has uniform composition throughout and thus only one phase or material is present, e.g. table salt in water. A homogeneous mixture is more commonly called a solution. A solution is composed of the solvent, which is the material present in the greatest quantity, and other substances or solutes, which are dissolved in the solvent, thus forming a solution. A pure substance has uniform composition throughout. Elements and compounds are pure substances. The composition of a mixture can be changed by physical means. The composition of a pure substance can not be changed by physical means, but can be changed by chemical means. It is important to note that all classes of matter can be interconverted by using chemical and physical means. The classes of matter are related as shown below.

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Physical Properties. A physical property of matter is any property of matter which is not a measure of the chemical nature of the matter. Physical properties are either extrinsic or intrinsic. An extrinsic property is any property that is independent of the actual nature of matter. Temperature, mass, volume, shape, etc., are common examples of extrinsic properties of bulk matter. An intrinsic property is any property inherent to the matter itself. Thus, intrinsic properties can be used to identify matter. Examples of common intrinsic physical properties include density, color, odor, melting-point and boiling-point temperatures.

Consider a sample of pure acetic acid which is the primary ingredient of household vinegar. Under normal laboratory conditions (standard temperature and pressure which is 0 °C and 1 atm) the acid is a colorless, sour-smelling liquid with a density of 1.05 g/mL. It also has a melting point of 17 °C, a boiling point of 119 °C, and is a moderate conductor of charge. If an unknown substance exhibits these exact properties, it virtually guarantees that the substance is pure acetic acid.

Chemical Properties. A chemical property is any property of matter, which is a measure of the chemical nature or “reactivity” of the matter. Reactivity is the tendency of the matter to change identity. All chemical properties are intrinsic. Examples of common, important chemical properties include acid (or base), oxidizer (or reducer), and the solubility. Again, consider pure acetic acid. The fact that this substance is called an “acid” indicates an important chemical property. It is also an oxidizer (as are most acids). Acetic acid is very soluble in water.

Physical Change. A physical change is any change in matter which is not associated with a change in the basic, inherent nature of...
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