Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards

Properties of Aqueous Solutions

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:

Properties of Aqueous Solutions
Students should measure properties of aqueous solutions, such as boiling point and freezing point, and deduce that they vary in a predictable way with composition and concentration. The phenomenon of diffusion should be investigated using easily distinguished solutes to establish that exchange occurs as a result of concentration gradients.

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