March 2020.  The Willets Lab visits Paul Holt's senior chemistry classes at Freire Charter School in Philadelphia for our annual "Adventures in Silver" featuring a new spectroscopy activity!
Interested in a visit from the Willets lab or copies of our procedures?  Email Kallie for more info!
Activity: We compared the behavior of silver on the macroscale to the nanoscale.

Experiment 1: Silver mirror.  Phil 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 2:  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.  They then prepared a second sample in which they added different volumes of KBr to their reaction solution to change the size (and final color) of their nanoparticles.

Experiment 3: Spectroscopy of silver nanoparticles. Students took uv-vis spectra of their nanoparticle solutions.  They used stickers to plot their spectral maximum vs. volume of added KBr on a master plot.  The results looked really awesome (see photo in upper right!).

Bonus experiment.  "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.

May 2019.  The Willets Lab visits Paul Holt's senior chemistry classes at Freire Charter School in Philadelphia for a lab on identifying unknown compounds

Activity:  Students were given one of eight unknown compounds and asked to identify it, using a series of chemical reactions as well as the flame test.  All they were told is that the unknown was a salt.

Cation identification.  Students started by recording the physical properties of their unknown solid, before dissolving it in water.  They then added NaOH to an aliquot of their solution and looked for precipitate formation.  This was followed by a flame test (with the help of our graduate student assistants!).  They then used a flow chart (shown at right) to identify the cation in their unknown salt.

Anion identification.  Students then divided their unknown solution into several additional aliquots and performed three different tests to determine the identity of their anion.  First they added HCl to one aliquot and looked for CO2 gas formation, indicative of the carbonate anion.  Next, they performed a barium chloride test, where formation of a white precipitate indicated the presence of sulfate anion.  Finally, they performed a silver nitrate test, looking for formation of a solid that indicated the presence of a halide anion.  Students learned the importance of controls as the different halides produced subtle differences in the color of the precipitate (white = chloride, cream = bromide, and yellow  = iodide). The flow chart (at right) helped them confirm their anion identity.  The students then balanced charges to come up with the final chemical formula for their unknown.
Note: Clicking photos enlarges them

October 2018.  The Willets Lab visits Paul Holt's senior chemistry classes at Freire Charter School in Philadelphia for a more advanced version of "Adventures in Silver"

Activity: We used three different approaches to prepare solid silver from solutions of silver nitrate. Students had to record their observations and form hypotheses about what they observed.

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.

June 2018.  The Willets Lab visits Paul Holt's freshman science classes at 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.