CHEM 237 EXPERIMENT #6 - Distillation
Post-lab Assignment - Spring 2010
Post-lab Questions: Answer these post-lab questions neatly and concisely on the back of
the lab report sheet. Use a blank sheet of paper if more space is needed to answer these
questions. Your answers will be evaluated and graded on quality, not quantity of
response! You are to complete this post-lab questions assignment individually. You
should work on this post-lab assignment as you would work on a take-home examination.
Write all responses in ink. Responses written in pencil [in part or whole] will be accepted
for a grade, but ANY and ALL requests for a regrade will be denied. This also applies to
responses written in pencil and then overwritten in ink and/or responses
obliterated with white-out-type materials and then revised.
Introduction: The instructor gave his CHEM 237 lab students 12.0mL of a ternary liquid
mixture with the following composition: octane, 40.0%; chloroform, 40.0%, and
isopropyl alcohol [aka 2-propanol], 20.0%. These values are all percent by volume. The
Experiment #6 post-lab assignment is worth eight points.
Post-lab Question #1. What is the composition of this ternary mixture on a percent by
mass basis? Show all necessary calculations. 1 point
Post-lab Question #2: What is the composition of this ternary mixture on a mole percent
basis? Show all necessary calculations. 1 point
Post-lab Question #3: Construct an ideal distillation curve for distilling 10.0mL of this
ternary mixture. 2.0 points
The students in an organic chemistry I lab were going to perform a distillation
experiment similar to the one you performed in Experiment #6. However, these students
were not given the normal boiling points of the two liquids in their unknown mixture.
Each pair of students was given 12mL of the unknown mixture.
Post-lab Question #4: Based upon your experience in having performed Experiment #6,
how would the students in this distillation lab experimentally determine the boiling
points of the two liquids in their unknown mixture? Hint: it might be helpful to include a
diagram with your answer. 2.0 points
Post-lab Question #5: Based upon your experience in having performed Experiment #6,
how would the students in this distillation lab experimentally determine the percent by
volume of each liquid in their unknown mixture? Hint: it might be helpful to include a
diagram with your answer. 2.0 points
Some thoughts on answering post-lab questions
 In many of the post-lab questions, you will be asked to provide an answer and an
explanation for that answer. In the past, many students have written prose
explanations. When you are writing your explanations, you should seriously think
about explicitly including a chemical structure(s) and or a chemical equation(s) in
addition to the prose as part of your explanation. Chemical structures and/or
chemical equations can be used to add a great deal of specific information to an
explanation in a way that pure prose cannot. In addition, chemical structures
and/equations can make your responses much each easier to understand.
 When you are writing your explanations for the post-lab questions, make sure you
include all necessary information. Do not answer a post-lab question with the
a
s
s
umpt
i
on…Idon’
tha
vet
oi
nc
l
udet
hat
,t
heTA wi
l
lknow what I mean. The TA
can evaluate and grade only what you have written, not what is not there.
 Audience: Even though a TA will evaluate and grade your post-lab question
responses, you should answer the post-lab questions as if you were providing that
explanation for a fellow organic chemistry I laboratory student. If a fellow organic
chemistry I laboratory student does not understand your explanation, then you need
to provide more specific information and/or rewrite your response in a more
understandable manner.
LABORATORY SAFETY
Any act of unsafe behavior, including failure to wear safety goggles when ever any
student is working, can result in dismissal from the lab. Students dismissed from the lab
for safety violations are eligible to take a make-up exam but a portion [five (5)] points
will be deducted from the score earned on the exam.