Return to Blog
Homepage
PCAT Chemical Processes – Recrystallization
- by
- Oct 25, 2017
- PCAT 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.
Explanation
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.
Related Post
Search the Blog
Free Consultation
Interested in our Online MCAT Course or one of our One-on-One MCAT Tutoring packages? Set up a free consultation with one of our experienced Academic Managers!
Schedule NowPopular Posts
-
-
-
-
-
MCAT Blog How to Review MCAT Full-Lengths
Free MCAT Practice Account
Need 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
Submit a Comment