The February 2015 issue of the Journal of Chemical Education is now available to subscribers at http://pubs.acs.org/toc/jceda8/92/2. The February issue includes content on: metal-organic materials, assessment, acid–base chemistry, game-based approach to teaching, chemical structure and properties, luminescence, inquiry-based teaching, nanochemistry, synthesis, and computational chemistry. This latest issue of JCE plus the content of all past issues, volumes 1 through 92, are available at http://pubs.acs.org/jchemeduc.
Students combine sodium carbonate and hydrochloric acid generating carbon dioxide gas which is allowed to escape. They measure the actual yield of carbon dioxide produced (missing mass), calculate the theoretical yield using stoichiometry, and then the percent yield. Students understand that 100% yield is the most appropriate answer (based on the Law of Conservation of Mass), so after considering the meaning of significant figures and the uncertainty of their measurements they are asked to decide if they did (or did not) get an answer that might indicate the validity of the Law.
One 50-minute period to perform the lab. One additional period to perform the calculations (optional). Often more able students will have time to begin some calculations at the end of the lab experiment.
Congratulations to Grazyna Zreda who solved the Chemical Mystery of the Mentos candies! To conduct this trick, two white Mentos candies are placed in separate beakers that both contain universal indicator. One of the Mentos candies turns the indicator slightly green, indicating the presence of base.