CHEM 2120U Lecture Notes - Lecture 1: Sand Bath, Sodium Sulfate, Weighing Scale

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4 Apr 2021
CHEM 2120 Experiment 1
Lab Skills: Report Sheet
1 | CHEM2120W21
Kuganesh Ketheesh & Student #: 100598968
* Please re-save this document with your name in place of ketheesh_kuganesh
Using the pictures and videos in the CHEM 2120 Exp1 Lab Skills W21 document, fill in the information below. You can
type you answers directly into this document or write it by hand; however, all submissions are done digitally through
Weighing Out a Sample: Describe the errors seen in the picture and explain the problems that could arise.
The problem with this is that the person is directly measuring out their solid on the analytical balance, this is an error because it is a
delicate equipment that may cause errors just simply by vibrations. A good weighing technique is very important to success in all
aspects of chemistry and the measurement of mass. For the greatest efficiency the proper balance must be chosen, and the
procedure must be done correct. The proper use of an analytical balance is to tare it to zero every time and to keep all the door
closed and to allow the mass to be analyzed within +- 0.0001g. By not closing the doors of the balance, air currents can affect the
measured mass if the person is leaning on the table that could also lead to many issues that would adversely affect the
measurement. Essentially, the person measuring out the solid should know that if they needed to still finish measuring out the
sample, they should do that beforehand. A great solution for this is if the person in the photo had performed weight by difference.
First, all they would have to do is weigh out the sample on an open pan balance, preferably using a small beaker or weighing vial.
The beaker should then be measured on the analytical mass with all door closed, so that vibrations from adding mass directly on
analytical balance and air current from keeping the doors open can be exempt. Furthermore, they would have to pour the contents
of the small beaker into a receiving vessel and simply re-weigh the now close to empty small beaker. Finally, they would have to
perform calculations in order to determine the amount of mass transferred by doing (mass of solid +beaker) subtract (close to
emptied beaker).
-Chemical spillage on an analytical balance can lead to different values for measurements at different times (it can lead to
fluctuation; this can go on to mess up any further calculations using the those mass values recorded. By using an open pan balance
and collecting the sample in a small vial or beaker before using the analytical balance you can ensure correct mass measurements,
especially ones that don’t change while you do continuous measurements.
In general, all step and procedures required in the lab to transfer and correctly measure a solid should be followed in as avoiding
using a analytical balance just in case to prevent any miscalculation due to errors such as chemical spillage as well.
Preparing a TLC Plate: Describe the errors seen in the two pictures and explain what would happen if the
experiment was allowed to run as shown.
The errors seen in the two pictures is that the spotted sample to be analyzed are not at the bottom but at the top.
The spots of the sample are not drawn on the line close to the bottom. They also have not labelled it at all. It cannot
be run because its upside down. Nothing will happen because the samples won’t even touch the solution placed
within in the jar. There will be no evident motion of the solvent line up the plate, this includes motion of the mobile
phase through the stationary phase. The solvent line will not even rise because it has been performed incorrectly.
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CHEM 2120 Experiment 1
Lab Skills: Report Sheet
2 | CHEM2120W21
Another error evident in the picture was the fact the TLC was not capped, which would lead to a low solvent vapor
pressure. The way this should have been done was the student should have had the TLC plate ready. They had the
right idea of how to place the plate in the jar itself with the cut side on the bottom going in first. However, they drew
the sample spot on the wrong side. The student should have drawn a line 1cm from the bottom of the plate. Then
they should have then proceeded to evenly space and place the sample spots along the drawn 1 cm line. Once that
one part is done then the experiment should work out by placing the plate facing down in the jar with the solvent
solution. Once the proper steps are followed then the motion of the solvent line up the plate is clear, this is the
motion of the mobile phase through the stationary phase is evident and clear as some time passes. Finally, if done
properly, it will result in raised solvent lines and should be taken out before it reaches 1cm from the top of the plate.
However, if the solvent line reaches the top of the plate you will have to restart to avoid erroneous results.
- The experiment should have been done in pencil instead the student used pen (may cause interference)
which can cause to errors in the lab after the plate has been put in the receiving flask.
- Labels have not been used under each sample so it may be confusing to differentiate and identify. This can
lead to errors when you’re trying to measure your values
- TLC jar was open, this could lead to errors that essentially decrease pressure in the container
- The TLC plate is upside down, so they are put in wrong. Also since the student used a pen this can also
lead to the solvents not being able to rise up with enough space or even move because they won’t be able
to go past the lines drawn on the opposite side (limits space to travel)
Using a Meltemp: Describe the errors in both experiments shown below and explain how running the experiment
with either sample would impact the obtained melting point.
Picture set #1 (Top):
Minimal amount is used which was good, but the compound does not look as if it is tightly packed to the bottom of
the capillary tube. It is packed at the open end of the tube, but it looks a little loose which can lead to air pockets.
The heat transfer within the compound will be different from the heat transfer through an air pocket. This would
essentially result in uneven heat distribution and it will lead to the inflation of the upper range of the melting point. It
also looks like they did tightly pack it at the bottom of the tube but kept it on the open end. The experiment will go
wrong because they are dropping the tube with the open side (the side with the sample) facing down and in first.
This will result in incorrect readings of temperature, which would later affect the student's ability to see the melting
point range for proceeding runs. The error in this would affect a student's ability to use the melting point of the
compound to determine the compound itself and the purity of the general, it looks as if the student
could have packed it more properly.
The way the tubes are placed was performed wrong by the student which could lead to errors in the lab , the student
may have to redo that portion of the lab.
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