June 2018. The Willets Lab visits Freire Charter School in Philadelphia for "Adventures in Silver"
Activity: We used three different approaches to prepare solid silver from solutions of silver nitrate.
Experiment 1: "Fuzzy" silver. Students coiled copper wire and immersed it in solutions of silver nitrate. Solid silver grew on the copper wire due to reduction of the silver ions. The solution turned blue due to oxidation of the copper wire to copper ions.
Experiment 2: Silver mirror. Joe and Vignesh prepared Tollen's reagent from silver nitrate, ammonium hydroxide, and sodium hydroxide, then added glucose. A shiny silver mirror formed on the inside of the vial. For safety reasons, we performed this experiment as a demo.
Experiment 3. Silver nanoparticles. The students followed the procedure from Kitaev and coworkers (J. Chem. Ed. 87 (2010) 1098-1101) to prepare silver nanoprisms. The color change is dramatic, going through multiple colors before forming a stable deep blue solution. We then compared the size of the nanoprisms to the size of a human hair . . . and the size of the teacher's head!
May 2017. The Willets Lab visits Freire Charter School in Philadelphia for a nanoparticle synthesis day
Activity: the students prepared silver nanoprisms following the procedure from Kitaev and coworkers (J. Chem. Ed. 87 (2010) 1098-1101).
Students started by preparing the same set of nanoprism solutions, in which no potassium bromide was added, and everyone successfully made blue solutions of silver nanoprisms. Then we allowed the students to pick varying amounts of potassium bromide to be added, yielding solutions of varying colors!! We finished with a discussion of the relationship between size and properties on the nanoscale (here, nanoprism size and color) as well as discussion of chemical synthesis.