Differentiating Pure Substances and Mixtures

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Objectives

At the end of the lesson, you should be able to:

  • distinguish mixtures from pure substances based on a set of properties; and
  • identify various method in separating the components of a mixture.

Pure Substance

  • It is always homogeneous.
  • It has uniform properties and definite composition.
  • It has a constant composition and combined chemically.
  • It cannot be separated into its components by chemical means.
  • It is either classified as an element or a compound.

Mixture

  • It has variable compositions made up of pure substances.
  • The pure substances that make up a mixture are combined through physical means.
  • Each pure substance in a mixture retains its properties.
  • It can be classified as solution (homogeneous), and colloids and suspension (heterogeneous).

Distinguishing Pure Substances and Mixtures

1. Atomic Level

  • An element is composed of only one kind of atom.
  • A compound is composed of two or more elements combined chemically.
  • A mixture is made up of two or more pure substances.

2. Composition

  • The composition of pure substances does not vary from one sample to another. It is uniform in any sample of a pure substance.
  • The composition of mixtures varies and the property of each constituent pure substance is retained.

3. Manner of Separation of Components

  • Pure substances cannot be separated by physical means.
  • Mixtures can be separated by physical means.

Separating Mixtures

1. Physical Separation

  • It separates the components of varying sizes using a spoon or any scooping material or by picking.
  • The use of magnet can be done to separate the metallic materials from non-metallic materials.

2. Filtration

  • It is a method to separate an insoluble solid from a liquid mixture using a semipermeable membrane like filter paper.

3. Decantation

  • It is a method used to separate large particles of insoluble solid from the liquid mixture.
  • The mixture is allowed to stand to separate the liquid layer from the solids that have settled.




Separating Mixtures

4. Evaporation

  • It is a method to separate the soluble solid from the liquid component of the solution by evaporating the liquid substance.

5. Distillation

  • It is a method to the components of a mixture of liquids based on the difference in boiling point.

6. Centrifugation

  • It is a method used to separate the components based on the difference in density.



Key Points

  • At the atomic level, an element is composed of only one kind of atom; a compound is composed of two or more elements combined chemically; and a mixture is made up of two or more pure substances.
  • The composition of pure substances does not vary from one sample to another. The composition of mixtures varies.
  • Pure substances cannot be separated by physical means. Mixtures can be separated by physical means.
  • Mixtures can be separated by physical separation, filtration, decantation, evaporation, distillation, and centrifugation.

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