|
Q: How long should
I heat the reaction mixture for?
A: Seven minutes, whether the mixture becomes clear or not. Sometimes
it will not become clear because the aspirin product starts to crystallize
out before all the salicylic acid solid is gone. So some of you will notice
your reaction mixture become clear, some will always have a white suspension
while heating. This may be due to how scratched the inside of the flask
is - many scratches would tend to promote faster crystallization of the
product.
Q: What if my solution
is clear and no solid comes out upon cooling?
A: Try scratching the inner surface of the flask with a glass rod - apply
enough pressure to hear some scratching noise. Or you obtain a seed crystal
from a neighbor and add it to your flask.
Q: Why do we chill
the precipitated aspirin before filtering?
A: For the same reason you wash with cold water: the aspirin has a certain
solubility in water, and we want to minimize our loss (which will be at
least 0.33g/100 mL of cold water anyway.)
Q: How many ferric
chloride tests do we do?
A: Four. Salicylic acid, crude aspirin, purified aspirin, and a blank
(95% ethanol only).
Q: If my salicylic
acid gives a purple color does this mean it has phenols in it?
A: No. Salicylic acid is a phenol: it has an OH directly attached
to a benzeneoid ring.
Q: Why won't my instructor
help me interpret my ferric chloride test?
A: He wants you to
interpret it. [Hint: draw structures and remember it is a test for phenols.]
©2001,2002 Daniel A. Straus
|