Today in class, we transformed the color of a copper penny to silver and then to gold. Following the steps outlined on page 6 of Lesson 2 of the textbook (A Penny for Your Thoughts), we immersed a 1979 penny (95% copper, 5% zinc) in a warm beaker of sodium hydroxide (3 M, about 40 mL) and zinc shot (enough to cover the bottom of a 150 mL beaker). After watching the penny change color to silver, tongs were used to transfer the penny to cool water. The penny was then transferred back to the hot plate (still set to 4) where it changed to a gold-copper color. The penny was placed back in cool water where it completed the transition to having a gold appearance. Students worked through most of the Lesson 2 worksheet in class. We wrapped up by making a list of questions students had about the experiment (pictured below). Those questions will form the basis for tomorrow’s lesson, where students will begin to probe how and why the penny changed color and whether the penny actually turned to gold. Students will write a hypothesis, carefully conduct the experiment documenting the steps they follow (the procedure), and then documenting the results of their experiment.
Remember, the PowerPoint from Lesson 1 is due tomorrow (9/11) by email.
Due Monday (9/14):
- Complete the Lesson 2 worksheet
- Answer questions 1, 2, 4, 5 on page 8 from Lesson 2
- Read Lesson 3
- Finish writing up the Friday experiment in student lab notebook for Monday check-off.
Monday (9/14): We modified the plan from Friday and decided to re-visit the demonstration approach for the Penny Lab. At the beginning of class, students were asked to share their hypothesis for the lab from last Friday. Students worked together to identify the manipulated and responding variables within their hypothesis statements, and a few brave students shared their variables with the class. We decided to use the class period to test whether pennies from the USA (pre-1982 and post-1982) exhibited different properties when placed in sodium hydroxide and zinc compared with pennies from Canada. We used Canadian pennies from 1965 and 2008 based on their differing metal composition (given in the picture below). We also crafted a class hypothesis statement and then wrote down each step of the experiment to document the procedure (below). At the end of the experiment, students described the color change and the pennies were photographed (also below). We wrapped up by noticing the color change in today’s experiment appeared to be inversely proportional to the amount of zinc in the pennies (i.e. the less zinc in the penny, the more gold color it became), thus completing one cycle of the scientific process.