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Lab 2 Optical polarimetry measurements on L-proline
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A copy of answers and feedback for laboratory of organic chemistry course.
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CHM 2123 –2022 – ReportOptical polarimetry measurements on L-proline
Student(s) Name(s) Asha Doughty
and Number(s) : 300226452
This report is: Individual
Date: October 6, 2022
Teaching Assistant: Samuel Delisle
Weekly Lab Period Thursday
COMMENTS
• Your report is submitted electronically via Brightspace into the dedicated folder.
• This report can be completed individually or in pairs, with your assigned lab partner, to each student’s
preference. If done in pairs, each student must submit an identical copy of the pre-lab. Make sure to include
both your names and student numbers above. Both students will receive the same marks and comments.
• This lab report is due on the week of October 3rd 2022, by the beginning of your respective lab section.
Do not trust Brightspace’s due date: since every students share the same Brightspace page, the due date
found online is for the last section of the week.
• Your results and discussion will cover both reactions done for this experiment. Type all the answers using
Arial font, size 12 pt, directly in the cells provided. The cells are representative of the length of the expected
answer, and their sizes have been locked to discourage superfluously long answers. Anything exceeding
this expected length may be ignored by the TA.
• Molecular figures must be drawn using ChemDraw.
• Late penalty is 20%/day, starting the moment the report is due and going up every 24h.
Point distribution
Introduction /7
Results /18
Calculations/Discussion /32
Consolidation Questions /14
Conclusion /3
TOTAL /74
, Introduction
Explain briefly what you did for this experiment, along with your objectives. (3 pts)
For this experiment, the goal was to determine the ratio of L-Proline in two mixtures: L-Proline
and NaCl, and L-Proline and D-Proline. In order to achieve this, 6 samples were analyzed
using a Vernier polarimeter. 4 samples containing pure L-proline in increasing concentrations,
one sample for the NaCl mixture, and one sample for the D-Proline mixture. From the cosine
squared function given by the Vernier polarimeter, a value of C was obtained, which was used
to calculate the angle of rotation for each sample. The concentrations of each sample and
their angle of rotations were plotted on a graph. A linear fit of the graph was used to calculate
the specific angle of rotation of L-Proline. Knowing the specific angle of rotation of L-Proline,
the quantity of L-Proline in each sample was calculated.
Explain briefly the technique used in this experiment; how it works, what you are measuring and
what it allows you to calculate, along with a brief description of the steps involved in the data
analysis. (4 pts)
In this experiment, optical polarimetry was used. When two enantiomers encounter polarized
light (which is chiral), they interact with the light differently. Optical polarimetry can distinguish
the enantiomers by measuring the angle in which they rotate the polarized light.
To do this, a Vernier polarimeter is needed. A polarimetry cell is inserted into the Vernier
polarimeter. The Vernier polarimeter shines polarized light through the cell. A disk on the top
is rotated clockwise which changes the intensity of light on a detector. The Vernier polarimeter
graphs the intensity of the light vs the rotation of the disk in a sinusoidal function. Then, the
graph is analyzed using a cosine squared fit.
The equation of the cosine squared fit gives a value C. The angle of rotation is calculated by
subtracting the C value of a blank (water) from the C value of the sample. Once the angle of
rotation is calculated, it is plotted against the concentration for the samples, leading to a linear
graph. The linear fit of this graph, y=mx+b, is analogous to equation 1 (α=[α]*l*c), allowing the
infereance that the slope of the linear fit is equal the specific rotation.
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