30 Jun 2015

The Messy Chemist: Separating a Solid Mixture

Lab Experiment

Submitted by Michael Norris, University of Washington
Categories
Description: 

This lab exercise gives students a problem scenario (a mixture of 4 solids) and asks them to determine a way to separate them from each other utilizing experimentation, previous knowledge, and discussion.  Students are expected to write a standard operating procedure detailing the method they determine for the separation at the end of the lab.  A modified version of this lab was originally performed in an accelerated summer class on chemistry given to 7th, 8th, and 9th graders that were on a track for early entrance into college.  The lab was done over the course of 2 days where students had about an hour each day to work in small groups on the lab and had to write the SOP as homework.  

AttachmentSize
File Separation Lab LO.docx22.27 KB
File Writing an SOP.docx16.74 KB
Learning Goals: 

Students will be able to:

·  Apply the concepts of polar and nonpolar solvents and differences in solubility to help      separate a solid mixture.

· Utilize a salt metathesis reaction to separate a complex cation from a solution.

·  Think critically and use team work to develop a plan to separate a mixture of solids based on  knowledge of solubility rules and experimentation.

·  Effectively communicate their procedure through writing a standard operating procedure.

Equipment needs: 

1.      Samples of test solvents: water, hexanes, and methanol

2.      Pure samples of the four substances in the mixture: sand, NaCl, 2,2’-bipyridine, and  [Fe(bpy)3](Cl)2

3.      NH4PF6

4.      9-10 small test tubes and test tube rack

5.      Marker for labeling test solutions

6.      Stirring rods

7.      Spatulas

8.      Three 10-mL graduated cylinders (one for each solvent)

9.      Two 100-mL beakers

10.  Other equipment dependent upon the procedure students develop

Implementation Notes: 

A modified version of this lab was originally performed in an accelerated summer class on chemistry given to 7th, 8th, and 9th graders that were on a track for early entrance into college.  The lab was done over the course of 2 days where students had about an hour each day to work in small groups on the lab and had to write the SOP as homework.  Students generally picked up the ideas quickly as it reinforced material they had previously been taught.  Most students came up with a plausible route to separte the solids in the mixture without any additional input.  In the lab I used in class, however, I did not include the salt metathesis reaction.  This may be a source of confusion particularly when calculating the mass% recovered at the end of the experiment.  Students also had some difficulty thinking about sources of error that matched their actual data.

It is also possible to add or remove instruction and leading questions depending on the level of students and how comfortable an inquiry approach is in the classroom.

Evaluation
Evaluation Methods: 

Students were required to turn in a written SOP following their experiment.  Emphasis in grading was placed on the explanations as to sources of error in the experiment as well as answers to the critical thinking question.  The goal is for students to demonstrate an understanding of the the methods used in the experiment and to think about why their data do or don't match the expected result.

Creative Commons License: 
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