Experimental Procedure

Estimated time to complete the experiment: 1 h



3 10-mL volumetric flasks 1 1-mL graduated pipet 3 Beral pipets 5 test tubes, 5 cm-long 1 Slide projector Aluminum foil

FeCl3 • 6H20 K3[Fe(CN)6] Na2H2EDTA 6 M NaOH D. I. water

Prepare 10 mL of an Fe(III) solution by adding 0.8 g of FeCl3 • 6H20 to 8 mL of H20 in a volumetric flask. Stir and dilute to the 10-mL mark. In another 10-mL flask dissolve 1 g of K3[Fe(CN)6] and dilute to the mark. Lastly, add 1 g of Na2EDTA to 5-6 mL of H20 in a third 10-mL flask, and add approximately 1 mL of 6 M NaOH to facilitate dissolution of the EDTA species; then, dilute to the mark. These procedures yield three solutions (approximately 0.3 M each) that should be enough for a large class because only one drop of each is needed. Caution: K3 (Fe(CN)e) is harmful by inhalation, ingestion and through skin contact.

Now, place approximately 1 mL of distilled water, one drop of the FeCl3 solution, and one drop of the K3[Fe(CN)6] solution in a 5-cm long test tube. Do this in duplicate (the second one is the blank test tube). Add one drop of the Na2 EDTA solution to each tube and shake. Wrap the blank test tube with aluminum foil so as to keep it away from light. Expose the other test tube to sunlight or to the light of an overhead projector (or of a slide projector). In a few minutes, a dramatic color change is observed. The blank test tube is then unwrapped, and the difference between both is annotated.



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