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 CaCO_{3} (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, MxCO_{3}, 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/

## Safety

### General Safety

General Safety

Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016). Some additional information on these guidelines can be found in a Pick at ChemEd X.

#### Safety resources

RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies

## NGSS

Engineering Design - Design a solution to a complex real-world problem is a performance expectation related to Engineering Design HS-ETS1.

Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

Using scientific knowledge to generate the design solution: Students restate the original complex problem into a finite set of two or more sub-problems (in writing or as a diagram or flow chart). For at least one of the sub-problems, students propose two or more solutions that are based on student-generated data and/or scientific information from other sources. Students describe* how solutions to the sub-problems are interconnected to solve all or part of the larger problem.

Describing criteria and constraints, including quantification when appropriate: Students describe criteria and constraints for the selected sub-problem. Students describe the rationale for the sequence of how sub-problems are to be solved, and which criteria should be given highest priority if tradeoffs must be made.