MCAT Chemistry Question — Recrystallization
- Nov 14, 2014
- MCAT Blog, MCAT Chemistry, MCAT Question of the Day
A student is having trouble successfully carrying out a recrystallization procedure. The student can improve the odds of success by doing each of the following EXCEPT:
A) Adding a seed crystal of the purified substance that he is attempting isolate.
B) Cooling the solution very slowly.
C) Submerging the beaker in a cool water bath.
D) Scratching the side of the beaker.
In a recrystallization procedure, a substance with impurities in dissolved in a small amount of hot solvent. The solvent is then very slowly cooled and the pure substance will crystallize out as its solubility decreases. To improve the outcome, the crytal needs a nucleation site to begin precipitating out. That can be provided either by scratching the wall of the beaker or by adding a seed crystal. Thus, (A) and (D) are incorrect.
If the solution is cooled too quickly, then both the pure substance and the contaminants may preciptate out all at once. Thus (B) is a way to improve the procedure, but (C), which would result in faster cooling would not solve the student’s problem. Thus (C) is the correct answer.
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.
Search the Blog
Free ConsultationSchedule Now
MCAT Blog How to Review MCAT Full-Lengths
Free MCAT Practice AccountNeed great MCAT practice?
Get the most representative MCAT practice possible when you sign up for our free MCAT Account, which includes a half-length diagnostic exam and one of our full-length MCAT practice exams.Learn More