Physical Separation Lab (Richard Hanley)

Richard Hanley (Del Sur Middle School, Lancaster, CA.)

NGSS Engineering Standards

Framework:

A. Defining and delimiting engineering problems involves stating the problem to be solved as clearly as possible in terms of criteria for success, and constraints or limits.

B. Designing solutions to engineering problems begins with generating a number of different possible solutions, then evaluating potential solutions to see which ones best meet the criteria and constraints of the problem.

C. Optimizing the design solution involves a process in which solutions are systematically tested and refined and the final design is improved by trading off less important features for those that are more important.

Materials needed

Beaker (of any size)

Iron Filings

Salt

Beyond that, is up to you. Suggestions include: access to a coffee filter or, even better, filter paper, a glass funnel, a separate beaker, a strong magnet, and a hot plate.

Procedure

I define the problem to students as using their lab group and any apparatus in the lab to separate out iron filings and salt which have been added to water (the amount of the solutes are up to you). I have them 'Think, Pair, Share' a solution to the heterogeneous mixture and then circulate the room to hear what they need and direct them to the equipment and/or supplies they need. The students invariably try to separate the iron filings through the use of a magnet but when wet, the iron filings are no longer magnetic. Some wish to evaporate out the water and then use a magnet to separate the filings from the salt. This, also, does not work as the filings have oxidized and are no longer magnetic (special care should be taken not to allow students to boil the solution dry or you'll break the beaker). Students who figure out how to patiently strain out the filings through filter paper and then evaporate the solution to get the salt correctly solve the problem as well. I have yet to have a group desalinate the water but that would be incredible. Optimization can occur through implementing a glass funnel to aid in the slow straining process.