Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


Recognition and Classification of Mixtures

Mixtures, Elements, and Compounds
Matter, as found in nature, consists primarily of mixtures, compounds, and elements in various proportions. The observable properties of mixtures depend upon the nature of the components. A mixture can be separated into pure substances using the characteristic properties of the substances contained in the mixture.


Further Description:

This grades 5--8 generalization should have been addressed before grade 9. Many students will need to review these concepts.

Pure substances possess a set of characteristic properties, such as melting point, boiling point, density, and chemical reactivity. The properties of mixtures will vary according to the types and quantities of their components.

Mixtures can be separated into purer substances by a variety of processes, such as chromatography, distillation, and crystallization. Mixtures can be classified as either homogeneous (solutions) or heterogeneous. The relative proportions of substances in solutions can be expressed in terms of concentration (percent by mass).

Many chemical processes occur in aqueous solutions. Understanding the nature of these solutions is important for understanding biological and geochemical concepts as well as environmental issues.


Concepts Needed:

Grade 9

Matter, compound, element, mixture, melting point, boiling point, concentration, percent by mass, solutions, homogeneous, heterogeneous, qualitative, quantitative, chromatography, distillation, substance, density, characteristic property, crystallization, solubility, viscosity

Grade 10

Concentration, colligative properties, concentration gradient, diffusion

Grade 11

Mole, molarity, molality

Grade 12

Vapor pressure, boiling point elevation, freezing point depression in solutions


Empirical Laws or Observed Relationships:

Law of definite proportions, law of multiple proportions


Theories or Models:

Particulate nature of matter


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Micro-Unit Description:

Recognition and Classification of Mixtures
Students should recognize solutions as mixtures and classify mixtures as heterogeneous or homogeneous (gas, liquid, and solid solutions). They should be able to separate mixtures into purer substances by a variety of processes, such as chromatography, distillation, and crystallization. They should observe that properties of mixtures vary with relative proportions (percent by mass) of the components.


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