Mixtures and Solutions

Goals:

Chemistry is the study of the structure of matter and the changes or transformations that take place in it. Learning about the makeup of substances gives us knowledge about how things go together and how they can be taken apart. Learning about changes in substances is important for several reasons: changes can be controlled to produce new materials; changes can be used to give off energy to run machines. The Mixtures and Solutions Module has four investigations that introduce students to these fundamental ideas in chemistry. (taken from FOSS program.)

Investigation 1: Separating Solutions

Investigation Summaries: Students make mixtures of water and solid materials (salt, gravel, and diatomaceous earth) and separate mixtures with screens and filters. They discover that water and salt make a special kind of mixture, a solution, which cannot be separated with a filter.

Students separate salt from water in a solution. They compare the total mass of a mixture to the mass of its parts. Students evaporate the salt solution.

Students observe salt crystals left when the water in a salt solution has evaporated.

Students are given a dry mixture (gravel, powder, and salt) to separate using the techniques of filtering and evaporating. (taken from FOSS program)

Investigation 1: Science Content

A mixture combines two or more materials that retain their own properties.

A solution forms when a material dissolves in a liquid (solvent) and cannot be retrieved with a filter.

Evaporation can separate a liquid from a solid in a solution.

The solid materials separated by evaporation from a solution forms distinctive patterns. (taken from FOSS program)

Investigation 2: Reaching Saturation

Investigation Summaries: Students make a saturated solution by adding salt to water until no more salt will dissolve. Using a balance, they find the mass of the solution to determine the amount of salt that dissolved in the solution.

Students make a saturated citric-acid solution. Using a balance, they compare the solubility of salt and citric acid by comparing the mass of the solid materials dissolved in the saturated solutions.

Students get an unknown material (Epsom salts), determine the mass of salt it takes to saturate 50 ml of water, and compare the value to other solids thus identifying the material.

Students observe citric-acid and Epsom-salt crystals and compare them to salt crystals. (taken from FOSS program)

Investigation 2: Science Content

A solution is saturated when as much solid material as possible has dissolved in the liquid.

Simple solutions are composed of two components: a liquid solvent and a solid solute dissolved in the solvent.

Solubility is the property that substances have of dissolving in solvents. Solubility is different for different materials and can change with temperature and different solvents.

Citric-acid and Epsom salt crystals have specific shapes and patterns.