CHE 231L DePaul University Chemistry Questions

CHE 231LLab 2: Separation of Two Unknown Liquid Compounds by Simple Distillation;
Characterization by Boiling Point and Density Determination
A. Pre-Lab Assignment:
1. Before coming to lab, read the following sections from Zubrick’s The Organic Chemistry Lab
Survival Manual:
Chapter 1 – Safety First, Last and Always
Chapters 4-6 – Jointware, Microscale Jointware, and Other Interesting Equipment
Chapter 11 – On Products
Chapter 19 – Clamps and Clamping
Chapter 20 – Distillation
Chapter 36 – Theory of Distillation
2. Prepare your notebook (Zubrick Chapter 2 – Keeping a Notebook) so that you are ready to
perform the experiment. While performing the experiment, use your notebook to record all data
and observations.
B. Specific Objectives:
Upon completion of this experiment, you will:
1.
2.
3.
4.
5.
Be able to effectively set up of a simple distillation apparatus.
Be able to identify all of the glassware needed to set-up a simple distillation.
Apply the theory of distillation.
Learn how to handle and store a liquid product.
Learn how to determine and record the boiling point range for an organic liquid.
C. Background:
A mixture of two miscible liquids can be separated and purified using simple distillation if the
boiling point difference between the two liquid components is sufficiently large, i.e. the difference
in boiling points is greater than 25 °C. When separating two miscible liquids by simple distillation,
the component with the lower boiling point will distill first when the mixture reaches the boiling
point temperature of that component. The observed vapor temperature will stabilize near the
boiling point of the lower boiling component while it distills. After the lower boiling component
has been completely distilled, the observed vapor temperature will decrease due to the absence of
any distilled vapors of the lower boiling component coming into contact with the thermometer.
What remains in the distillation flask is the higher boiling component, which will heat until it
reaches its boiling point and begin to boil, vaporize, and ultimately distill as well. The goal is to
stop the distillation before the second, higher boiling component begins to distill. This is achieved
simply by removing the distillation flask from the heat immediately after the lower boiling
component has completely distilled, indicated by a significant drop in observed vapor pressure
from the stabilized boiling point temperature. When the distillation is complete, the lower boiling
component is contained in the receiving flask and the higher boiling component remains in the
distillation flask.
D. Experiment:
You will obtain a mixture of two unknown liquid compounds, one with a low boiling point and
the other with a high boiling point, and separate them using simple distillation. Once separated,
you will characterize each by measuring the boiling point temperature range of each unknown
liquid compound as well as the density of each.
E. Procedure:
1. Mass the distillation flask (containing ~5 boiling stones) and the receiving flask (empty).
Make sure these flasks are appropriately sized. Record their masses in your notebook.
2. Obtain your assigned unknown liquid mixture. Record your assigned unknown liquid mixture
code in your notebook.
3. Describe the appearance (e.g. color, odor, viscosity, etc.) of your mixture of liquid unknowns
and record this in your notebook.
4. Determine the mass of the unknown liquid mixture by transferring it into the distillation flask.
Subtract the mass of the distillation flask from the mass of the flask containing the mixture.
Record the difference as the mass of the unknown mixture in your notebook.
5. Assemble the simple distillation apparatus as you did in lab 1.
a. Place your distillation flask in the heating mantle so contact is made. Then add sand so
that the entire level of liquid is submerged in sand.
6. Insulate the top of the distillation flask and distillation adapter by loosely wrapping both
with aluminum foil. Leave a small window so that you can observe the distillation flask.
7. Turn the temperature/power dial on the base of the hot-plate to 200 – 225 °C. Be sure that
your hood sash is closed to minimize airflow (cooling) across your set up. Increase the
temperature as needed if distillation takes too long to start.
8. Carefully begin heating the distillation flask on a hot plate
9. Record the stabilized vapor temperature range of the lower boiling point component as the
distillation proceeds.
10. When you observe a steady drop in temperature continue heating for 5 min to distill any
remaining lower boiling compound to complete distillation.
11. Turn off the heat and raise the distillation flask out of the heating well. Allow the glassware to
cool to room temperature.
12. Record the mass of the distillation flask and the receiving flask and determine the mass of
liquid in each by subtracting the mass of the empty flasks. Record these values in your
notebook.
13. Calculate a percent recovery by dividing the sum of the masses of each liquid by the mass of the
original mixture:
percent recovery (%) = [mass of component (g)]/[mass of mixture (g)] x 100%
14. Transfer each liquid to a separate, labeled vial (include your name, the date, section number,
and the contents of the vial). Take care in labeling which liquid is the lower boiling
temperature compound and which is the higher boiling temperature compound.
15. Determine and record the boiling points of each liquid using the following procedure:
a. Transfer approximately 2 mL of the lower boiling liquid unknown into a test tube.
b. Add 2 or 3 boiling chips to the test tube.
c. Set the test tube in the sand bath and clamp it in place. Alternatively, clamp the test tube in
an aluminum block directly on the hot plate (not using the sand bath) as depicted in Figure 1
below.
d. Clamp a thermometer probe so that about 1 cm of the tip of the probe is submerged below e.
the surface of the liquid. Do not allow the thermometer probe to come into contact with the
interior surface of the test tube.
e. Gently heat the liquid slowly and carefully until it boils.
f. When the liquid begins to boil, monitor the temperature.
g. Once the temperature reaches a plateau and stabilizes around a peak temperature range
for at least one minute, record that temperature range as the boiling point of the liquid.
h. Repeat steps a. to f. with your higher boiling unknown liquid.
16. Determine and record the density of both unknown liquids using the following procedure:
a. Using a Pasteur pipet, carefully fill a 1 mL volumetric flask with acetone to clean. Discard in
waste container and allow to dry.
b. Measure the mass of the dry, clean 1 mL volumetric and stopper. Record this mass in your
notebook.
c. Fill the dry, clean 1 mL volumetric flask with one of your liquid unknown. Fill to the
meniscus and stopper. Record the mass of this stoppered flask in your notebook.
d. Divide the mass in grams by the volume in milliliters to obtain the density in g/mL.
Density (g/mL) = [mass of aliquot (g)]/[volume of aliquot (mL)]
e. Using a Pasteur pipet remove your unknown and return it to your sample vial.
f. Repeat steps a. to e. for your other unknown
17. When done with samples, screw cap tightly and parafilm the top. Hand samples to
instructor or TA.
18. Clean all glassware used. Clean up your bench, make sure everything is put away in its
proper storage container, and have your instructor or TA check your area and sign your
notebook pages. Turn in your notebook carbon copies.
Figure 1. Apparatus for boiling point temperature range measurement.
CHE 231L
Assignment 2
Writing Assignment 2
Writing an Abstract
The abstract section of a scientific paper (lab reports included) is arguably one of the
most challenging to compose. Although the abstract appears first in most scientific
manuscripts (after general information and the title of the work), it is often written last by
the author(s). This is because the abstract is meant to provide a brief and concise summary
of the work being reported – it is a way to let the reader know if he/she wants to read the
entire manuscript. Here are a few tips on writing a proper abstract:
•
•
•
•
The abstract should be 100-250 words in length.
The abstract succinctly states what was done, how it was done, and what the
results were, but no detailed procedural information should be included.
Typical data presented in the abstract for an organic chemistry publication would
include, but is not limited to, synthetic and analytical techniques employed in the
experiment, method(s) of purification, yield of the reaction(s), physical data for
products, and for research aimed at elucidating the identity of an unknown a brief
comment of what spectroscopic technique enabled you to determine the identity.
See the sample abstract below:
“4-Nitrotoluene was synthesized from toluene and nitric acid through the process
of electrophilic aromatic substitution, catalyzed by sulfuric acid. The crude
product was recrystallized from ethanol to give a yellow crystalline solid (MP =
50 – 54 °C) in 85% yield. IR spectral data of the pure product were consistent with
the literature values for 4-nitrotoluene.”
Assignment:
Write a sample abstract based on the experiment performed on the videos for Module 1
(Separation of Liquids via Distillation). Use the above example as a guide. Make sure to
only include the most important data collected during the experiment: the percent
recovery, BP and density of the LBP and HBP liquids.
Formatting: It should be written in past tense using a passive voice. This assignment
should be double-spaced and typed using Times 12-point font with 1” margins all around.
You may use the space below to write the abstract.
CHE 231L
Assignment 2
Name:_________________________________
Abstract:
Rubric for Assignment 2
Component
Points
Formatting
/3
Typos/grammar
/2
Content
/5
Total
/10
Guidelines
-1 pt for length
-1 pt each for tense and voice
-1 pt for incorrect font or spacing
-0.5 pt for each error up to -2
-2 pts for including procedural information
-1 pt each for missing data: bps, densities,
yields
*Add a copy of this rubric and attach it to the front of your assignment!*