SCF To Use IR Spectroscopy to Identify Organic Compounds Lab Report

Description

Lab Title: Measurements of Physical Properties
Purpose of the Lab:
To become familiar with the laboratory techniques associated with the
determination of certain physical properties of organic substances –
boiling point, melting point, refractive index and density.
Equations:
Density = mass/volume (g/mL)
Refractive Index = observed nD+(room temp-20 C)*0.00045
List of Materials and Chemicals:
Capillary tubes, 10 uL syringe, test tube, centrifuge, disposable pipets,
Uni-Melt Apparatus, hinged sample prisms, refractometer, coverslips,
tweezers, forceps, 20 uL Drummond Pipet with bulb, 10 mL beaker
Apparatus:
Chemicals:
ORGANIC COMPOUNDS
INORGANIC COMPOUNDS
Chemical Name: Acetanilide
Chemical Name:
Formula: C6H5NH(COCH3)
Formula:
Molecular Weight:
Structure:
Molecular Weight: 135.17 g/mol
Boiling Pt: 304 C
Melting Pt: 114.3 C
Density: 1.22 g/cm^3
Solubility:
Solubility: water
Refractive Index: 1.576
Reference:
http://en.wikipedia.org/wiki/Acetanilide
Chemical Name: Heptane
Formula: C7H16
Structure:
Molecular Weight: 100.21 g/mol
Boiling Pt: 98.42 C
Melting Pt: -90.1 C
Density: 684.00 kg/m^3
Solubility: water
Refractive Index: 1.387
References:
http://en.wikipedia.org/wiki/Heptane
Chemical Name: Octane
Formula: C8H18
Structure:
Molecular Weight: 114.23 g/mol
Boiling Pt: 125.1 C
Melting Pt: -57.1 C
Density: 0.703 g/cm^-3
Solubility: water
Refractive Index: 1.398
References:
http://en.wikipedia.org/wiki/Octane
Chemical Name: Methanol
Formula: CH4O
Structure:
Molecular Weight: 32.04 g/mol
Boiling Pt: 64.7 C
Melting Pt: -97.6 C
Density:0.7918 g cm^-3
Solubility: water
Refractive Index: 1.33141
Reference:
http://en.wikipedia.org/wiki/Methanol
Procedure:
METHOD
A. Ultra Micro BP
1. Place 3-4 uL heptane into capillary
OBSERVATIONS
We did not do this experiment
tube using 10 uL syringe
2. Place cap tube upright into a 13 x 100
mm test tube. Insert tube into centrifuge
and get sample to bottom of tube
3. Make 2 glass bells by heating a
disposable pipet and stretching it so that
it will fit into the open end of cap tube
4. Cut each bell to 5 mm long and fuse
one end of each bell
5. Insert the 1st bell into the cap tube,
open end down, tapping tube so that the
bell falls to the bottom of the cap tube
6. Place the cap tube into a UniMelt
Apparatus
7. Raise the temp until it is approx 15-20
C below the referenced BP
8. Slow the rise in temp so that the
increase is 2 C /min
9. Keep raising the temp until fine
stream of bubbles coming from bottom
of bell
10. Reduce temp gradually and record
the temp where the last bubbles escapes
from the bell
B. Refractive Index
1. Turn on – light at end of arm will come
on
2. Open the hinged sample prism
3. Using disposable pipet place a sample
of methanol on the prism of the
refractometer
4. Close prisms slowly
Boiling Point =
5. Raise the light on the end of the
moveable arm so that the light
illuminated the upper prism
6. Look in the eyepiece and slowly turn
the large scale arm trying to bring the
separation between the light and dark
halves into the center of the crosshairs
7. Press and hold scale/sample field
switch. Read refractive index to 4th
decimal
Refractive Index = 1.3285
8. Record the temp of the cell and if
different from 20 C use formula
Temp of cell = 20.9
nD+(room temp-20 C)*0.00045
1.3285 +(20.9-20)*0.00045 = 1.3289
Corrected Index (due to temp) = 1.3289
C. Melting Point
1. Try not to touch coverslips – use
tweezers
We used the capillary tubes for this
experiment
2. Place clean coverslip in the well of the
stage
3. Place a few crystals of acetanilide on
the coverslip
4. Place another coverslip on top of
crystals
5. Set the voltage control to zero
6. Raise the temp rapidly to 15-20 C
below the expected MP
7. Slow the temp rise to 2 C/min
8. Record the temp at which the first
crystals start to melt
Temp when first crystals melt = 114.1 C
9. Record the temp at which the last
crystals melt
Temp when last crystals melt = 115.2 C
10. MP is actually a temp range
The crystals melted very quickly
11. Turn the switch to OFF and set
voltage control to zero
12. Let stage cool and remove sample
13. Make sure you take into account any
correction factor listed on apparatus
No correction factors listed on appartus
D. Density
uL = micrometers
1. Do not handle pipet with fingers
Wore gloves. 20uL = 20 x 10^-3 mL
2. Weigh an empty 20 uL Drummond
Pipet with a bulb in a 10 mL beaker
Initial weight = 11.7322 g
3. Draw the octane into the pipet by
tilting sample container sideways and
allowing cap action to draw liquid up to
the black line on pipet
We did this very quickly so that octane
didn’t evaporate
4. Transfer the pipet to the pre-weighed
10 mL beaker for the final weighing
Final weight = 11.7382 g
Pre-Laboratory Questions
1. What are the two main reasons for doing a melting point?
The determination of physical properties such as melting point helps the
research scientist identify the substance and it will also indicate how pure the
substance is.
2. What is the effect of an insoluble impurity on the melting point of a compound?
The insoluble impurity will not have an effect on the melting point of a
compound. On the other hand, a soluble impurity will melt at lower temperature
and it will also melt over a wider range of temperatures.
3. Which of the following determinations is most accurate when it comes to
identifying a compound? Why?
a. melting point
b. refractive index
c. boiling point
The refractive index would be the most accurate since it is recorded to the fourth
decimal place.
4. Why should you calibrate a thermometer and suggest how you might calibrate a
melting point thermometer.
You need to calibrate a thermometer so that you do not have variations in
temperature. Calibrations update the indications and allows the user to maintain
accurate results when making temperature measurements
5. What is the value of the refractive index shown in Figure 5? 1.3433
Data Table 2 (Refractive Index Determination)
Compound: Methanol
Determined Value: 1.3285
Corrected Index (due to temp) = 1.3289
CRC: lit. value 1.3306
; Ed. 3rd
; Page 80
; Compound No. 1
Aldrich: lit. value 1.329
; Year 2008 ; Page 1752 ; Compound No. 67-56-1
Merck: lit. value 1.3292
; Ed. 15th
; Page 1106 ; Compound No. 6029
Data Table 3 (Melting Point Determination)
Compound: Acetanilide
CRC: lit. value 114 C
Determined Value: 114.1 C – 115.2 C
; Ed. 3rd
; Page 235 ; Compound No. 174
Aldrich: lit. value 113-115 C; Year 2008 ; Page 19
; Compound No. 103-84-4
Merck: lit. value 113-115 C ; Ed. 15th
; Compound No. 103-84-4
; Page 10
Data Table 4 (Density Determination)
Density (g/mL)
Methylene Chloride (CH2Cl2)
1.33
Octane (C8H18)
?
Weight of filled pipet and bulb: 11.7322 g
Weight of empty pipet and bulb: 11.7382 g
Weight of measured liquid: 0.0060 g
Volume of liquid: 20 x 10^-3 mL
Determined Value: 0.3 g/mL
CRC: lit. value 0.70252 ; Ed. 3rd
; Page 4
; Compound No. 82
Aldrich: lit. value 0.703
; Year 2008 ; Page 2029 ; Compound No. 111-65-9
Merck: lit. value 0.7028
; Ed. 15th
; Page 6838 ; Compound No. 111-65-9
Post-Laboratory Questions
1. Why is it necessary to correct the measured refractive index for temperature
before comparing it to known values?
It is necessary to correct the measured refractive index for temperature so that
you get an accurate index.
2. If methylene chloride was used to extract an aqueous phase would the
methylene chloride layer be on the bottom or the top?
The methylene chloride layer would be on the bottom since its density is 1.33 g /
cm^3.
3. If octane was used to extract an aqueous phase would the octane layer be on the
bottom or the top?
The octane layer would be on the top since its density is 0.7 g / cm^3
4. You have an unknown substance you think is acetanilide. Can you devise a
technique to confirm your suspicion by melting point alone?
No you would not be able to confirm the substance by using melting point alone
since it is not always accurate due to impurities and it also melts within a range
of temperatures.
Interpreting FTIR Spectra
Background: Interpreting FTIR spectra is a skill that often requires some amount of practice, which, in turn,
necessitates access to a collection of FTIR spectra. Virtual ChemLab has a spectra library containing more than
700 FTIR spectra. In this assignment, you will take advantage of this by interpreting the FTIR spectra of five
similar compounds with different functional groups. After completing this assignment, you may wish to select
other compounds for additional practice.
Purpose: To identify organic compounds by their functional group using IR spectroscopy
Materials
Apparatus: IR Spectrometer
Chemicals:
a. Benzaldehyde
b. Benzyl Alcohol
c. Benzoic Acid
d. Acetophenone
e. Benzyl Amine
Procedure:
1. Start Beyond Labz.
2. Click on the Organic Qualitative Analysis tab (Lower left of the screen).
3. Click on “Alcohols”.
4. Using your mouse click on benzyl alcohol. You should see liquid in the flask.
5. Using your mouse click and drag the IR disc from the instrument to the middle of the round bottom
flask.
6. Capture the image for your lab report.
7. Fill in Data Table with major absorptions.
8. Repeat steps 3-9 for the following compounds by clicking on the appropriate pull down for the
functional group.
a. Aldehyde: Benzaldehyde
b. Ketone: Acetophenone
c. Carboxylic Acid: Benzoic Acid
d. Amine: Benzyl amine
Pre Lab Questions:
1. Can you predict the exact structure of a compound using IR? Why or Why not?
2. Which appears at higher wavenumbers bending or stretching and why?
3. What types of energy changes occur in the IR
Post Lab Questions:
1. How would you distinguish between an alcohol and an amine in the IR?
2. How would you distinguish between an aldehyde and a ketone in the IR?
3. How would you distinguish between an acid and an ester in the IR?
1
FTIR Tables
Compound: Benzaldehyde
Absorption in wavenumbers, cm-1
2 peaks at 2800 cm -1
1 peak 3050 cm -1
Type of Absorption
C-H Stretch of the Aldehyde
C-H stretch sp2
Compound:
Absorption in wavenumbers, cm-1
Type of Absorption
Compound:
Absorption in wavenumbers, cm-1
Type of Absorption
Compound:
Absorption in wavenumbers, cm-1
Type of Absorption
Compound:
Absorption in wavenumbers, cm-1
Type of Absorption
2
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