Chemistry – Mr. Hobson Pure Substances Physical Properties Physical Changes Mixtures Separation Techniques

Everything that has mass and volume is called matter.

Matter that has a definite and uniform composition are substances. Substances can be identified as either an element, compound, or a mixture.

 Fixed composition  Cannot be separated into simpler substances by physical methods (physical changes)  Can only be changed in identity and properties by chemical methods  Properties do not vary

A physical change occurs when the substance changes state but does not change its chemical composition. For example: water freezing into ice, cutting a piece of wood into smaller pieces, etc. The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)

 A physical property is a quality or condition of a substance that can be observed or measured without changing the substance ’ s composition.  Physical properties may be intensive or extensive.

 Melting point  Boiling point  Vapor pressure  Color  State of matter  Density  Electrical conductivity  Solubility  Hardness

 Length  Height  Width  Weight  Area  Volume  Mass  Circumference

Mixtures are two or more substances that are NOT chemically combined. Mixtures do not: Have constant boiling points Have constant melting points

 Variable composition  Components retain their characteristic properties  May be separated into pure substances by physical methods  Mixtures of different compositions may have widely different properties

Homogeneous mixtures look the same throughout. Only one “phase” is present. Phase: part of a sample with uniform composition and properties. Homogeneous Mixture can be separated by physical means. Examples: Kool-Aid, Milk, Black Coffee.

Solutions are homogeneous mixtures. These mixtures are usually created when something is completely dissolved in pure water. A solution has 2 parts: Solvent (does the dissolving) Solute (gets dissolved)

Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, filtration, metallic properties). Examples: Vinegar/Oil Salad Dressing, Vegetable Soup, Pizza

 Do not have same composition throughout  Components are distinguishable (2 or more phases are present)

 Mixtures can be separated by the differences in their physical properties.  There are numerous techniques available.  Filtration, Evaporation, Condensation, Distillation

 The process that separates a solid from the liquid in a heterogeneous mixture is called filtration.

 This method is suitable to separate a soluble solid from a liquid.  The process of a liquid converting to its gaseous state.  This can usually be accomplished by raising the temperature of the liquid or solution.

 Change of the physical state of matter from its gaseous phase into its liquid phase.  This is usually accomplished by lowering the temperature.

 Method of separating mixtures based on differences in their boiling points.  Distillation is the process of heating a liquid until it boils, capturing and cooling the resultant hot vapors, then collecting the condensed vapors.  In other words: Evaporation followed by Condensation.