Return to MCAT® Blog Homepage

MCAT Chemistry Question — Excess Reagents

A chemistry student is carrying out several reactions in the lab. At the end of his work, he has excess of three reagents: X, Y, and Z. The student examines the beakers with each reagent. X is a clear liquid and looks to be fine, so he pours X back into the stock bottle in the storage room. There is very little Y left, so he pours it down the drain with lots of water. Finally, there is a significant amount of Z left, but the student knows that Z is a volatile liquid, so he leaves it on the lab bench overnight, knowing that it will have evaporated by the time he returns in the morning. Which of the following correctly characterizes the student’s choices:


A) The student properly dealt with reagent X and Y but not Z. Open containers of excess reagents should never be left sitting out on the lab bench overnight.
B) The student properly dealt with reagent Y but not X nor Z. To avoid contamination, reagents should never be returned to the original stock bottle, and leaving a beaker unattended is a safety risk.
C) The student properly dealt with reagent X but not Y nor Z. Reagents should not be flushed down the sink and they should not be left unattended overnight.
D) The student did not properly deal with any of the excess reagents.




Waste materials in the lab should be disposed of in properly marked waste containers. The student did not deal correctly with any of the reagents. Returning it to the stock bottle risks contamination, pouring it down the drain risks damage to the plumbing or (eventually) the environment, and leaving it sitting out on the lab bench is all sorts of dangerous. Therefore, the answer is (D).


Want more MCAT practice?

We’ve got options for every schedule and learning style!

From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT Advisor using the form below. No obligation, just expert advice.

Schedule My Free Consultation

MCAT is a registered trademark of the Association of American Medical Colleges (AAMC), which is not affiliated with Blueprint.