The process by which one calculates the limiting reagent, theoretical yield and excess reagent must be revisited periodically to keep this ability in one's long-term memory. While this has traditionally been accomplished with untimed homework problems, the proliferation of sites that provide solutions to homework problems has resulted in some students getting the correct answer without altering their long-term memory. In collaboration with Chem21Labs users, we have begun to create iTRQs (interactive TRQs) where students perform a series of steps in a span of time (e.g. 50 - 200 seconds) that is longer than the normal TRQ time.
In the Limiting Reagent iTRQ, if students can correctly answer the question before the timer reaches 0 seconds, they wil have completed the assignment. If they don't answer the question correctly, they are transitioned to a page where they are guided through the individual steps of the cacluation with immediate feedback. They then repeat the iTRQ - either getting the answer correct on the first page (without guidance) or correctly completing the individual steps (with guidance). If the student correctly answers the problem on the first page, they are finished and receive full credit on the assignment. Alternatively, if the student completes the step-by-step second page a certain number of times (e.g. 4), they are also finished and receive full credit on the assignment.