For my students and me, the AP Chemistry exam does not mark the end of the school year. Once the AP exam is over, my students are exhausted but our class continues to meet for three more weeks. Each year we complete a qualitative analysis lab, but this year we finished earlier than I anticipated. For the first time all year, I have the luxury of time. I decided to go back to one of the resources I wrote about previously - the International Chemistry Olympiad released exams. I have adapted some Laboratory Challenges from these previous exams. The first asks students to identify an unknown solid using a balloon and some string.
Gas Laws, Solubility
45 minutes or less
• One 50-mL beaker (to contain the 3.0 M HCl)
• 1.00-1.20 g of unlabelled CaCO3 (This is the unknown the students will idenitfy)
• One 10-mL graduated cylinder
• One balloon
• One scissors
• One metric ruler with mm precision
• One length of string approximately 30 cm (12”) in length
• 2-3 weigh boats
• One metal scoopula
• Access to a 0.01 or better electronic balance
• Access to distilled water
Students will be given a small sample of solid, powdered unknown metal carbonate, MxCO3, 3.0M hydrochloric acid, a balloon, and some laboratory equipment. The challenge is to devise and carry out an experiment to determine the volume of gas produced and identify the carbonate by combining the two chemicals. The possible metals are Ba, Ca, Li, and Na.
Students will create a procedure to solve the problem.
Pour the HCl into the 50 mL beaker. The CaCO3 should be powdered, not granular or in rock form. Do not label or identify the carbonate. Stretch the balloon a few times to make sure it will inflate. Students should wear goggles.
2008 UNSCO Exam, available at: http://www.acs.org/content/dam/acsorg/education/