Then give them the mixture and the equipment they require to do the separation. As an alternative, each group could be given a different type of mixture to separate. Some combinations are salt and pepper, sand and salt, sand and staples, vermiculite and plastic beads, sand and iron filings, salt and iron filings, sand and sawdust. Students must devise their own procedures to separate the mixture. Provide each group with a variety of substances which undergo phase changes at, or near, room temperature.
Examples are dry ice, moth crystals, ice cubes, water, and rubbing alcohol.
Ask each group to describe the observations which indicate that a phase change is occurring. A list of phase changes which the group members identify from their experience can be compiled. Discuss the factors which influence the rate of the change. If dry ice is used, make sure that the students do not touch it to bare skin. In larger centres, dry ice may be obtained from welding supply stores.