The objective of this experiment is to determine the flooding point and the velocity of flooding through observation and experimental data. Apart from that, it is also used to study the effects of ...
This experiment will measure the absorption of infrared light by salicylic acid and acetylsalicylic acid. A commercial aspirin tablet containing both of these molecules will be analyzed and the spectra will be compared.
Infrared (I!& radiation with wa+elengths of ,%% nm to -%%%% nm is found in the electromagnetic spectrum between the +isible and microwa+e regions. It can be applied
to the analysis of organic molecules by causing molecular rotation and/or molecular +ibrations (stretching or bending of bonds& in the molecules.
PROCEDURE:
The operating manual and the instruction for the operation of the instrument ha+e been thoroughly read before beginning the experiment.
A. Preparation of KBr Pellet
In order to measure the absorption of the sample a transparent sample container material has been used to infrared radiation. )*r is used since it has excellent transparency in the I!. Solid samples are measured by grinding the sample into a fine powder and mixing a small amount of sample powder with powdered )*r. 0. *lan1 )*r 'ellet a. 2%% to 3%% mg of )*r was grinded into a fine powder using a mortar and pestle. b. The operating instructions were followed to create a )*r pellet. 2. Salicylic Acid in )*r 'ellet a. 2%% to 3%% mg of )*r was grinded into a fine powder using a mortar and pestle. b. 0 to 2 mg sample of Salicylic Acid was also grinded into a fine powder. c. The Salicylic Acid was added to the ground )*r and mixed by grinding the mixture. d. The mixture was pressed into a )*r pellet.
Same procedure is repeated by using ommercial Aspirin tablet as solid sample.
B. O!tain IR Spe"tra
The instruction on how to use the Fourier Transformed Infrared Spectrophotometer (FTI!"#$%%S Shimadzu& had been gi+en by the instructor before the experiment started. All the spectra were obtained using the following parameters and sa+e all scans. !ange $-%% cm "0 4umber of Scans 05
0.
IR Ba"#$ro%n& Spe"tr%': The bac1ground I! spectrum was obtained without a
sample in the instrument. (. Pol)t)rene Cali!ration *il' Spe"tr%': i. The polystyrene calibration film was placed in the sample holder and obtains the spectrum at a resolution of 05.% cm "0. 3.
Blan# KBr pellet Spe"tr%' The blan1 )*r pellet was placed in the sample
holder and the spectrum was obtained. $.
Sali")li" A"i& Spe"tr%' The salicylic acid/)*r pellet was placed in the sample
holder and the spectrum was obtained. -.
Co''er"ial Apirin Spe"tr%' The aspirin /)*r pellet
sample holder and the spectrum was obtained.
was placed in the
*LO+ C,ART
DISCUSSION -UESTION
0. S1etch the main spectrophotometer.
components
of
an
FTI!
infrared
absorption
The basic components of an FTI! are shown schematically in Figure 0. The infrared source emits a broad band of different wa+elength of infrared radiation. The I! source used in the Temet 6ASM7T FTI! !"series is a Si ceramic at a temperature of 0--% ). The I! radiation goes through an interferometer that modulates the infrared radiation. The interferometer performs an optical in+erse Fourier transform on the entering I! radiation. The modulated I! beam passes through the gas sample where it is absorbed to +arious extents at different wa+elengths by the +arious molecules present. Finally the intensity of the I! beam is detected by a detector which is a li8uid"nitrogen cooled MT (Mercury"admium"Telluride& detector in the case of the Temet 6ASM7T FTI! !" series. The detected signal is digitised and Fourier transformed by the computer to get the I! spectrum of the sample gas.
Figure 0 *asic components of FTI! A common FTI! spectrometer consists of a source interferometer sample compartment detector amplifier A/9 con+ertor and a computer. The source generates radiation which passes the sample through the interferometer and reaches the detector. Then the signal is amplified and con+erted to digital signal by the amplifier and analog" to"digital con+erter respecti+ely. 7+entually the signal is transferred to a computer in which Fourier transform is carried out. *i$%re ( is a bloc1 diagram of an FTI! spectrometer.
*i$%re (. *loc1 spectrometer
diagram of an FTI!
The ma:or difference between an FTI! spectrometer and a dispersi+e I! spectrometer is the Michelson interferometer .
Michelson Interferometer
The Michelson interferometer which is the core of FTI! spectrometers is used to split one beam of light into two so that the paths of the two beams are different. Then the Michelson interferometer recombines the two beams and conducts them into the detector where the difference of the intensity of these two beams is measured as a function of the difference of the paths. *i$%re is a schematic of the Michelson Interferometer.
*i$%re . Schematic of the Michelson interferometer
A typical Michelson interferometer consists of two perpendicular mirrors and a beamsplitter. ;ne of the mirrors is a stationary mirror and another one is a mo+able mirror. The beamsplitter is designed to transmit half of the light and reflect half of the light. Subse8uently the transmitted light and the reflected light stri1e the stationary mirror and the mo+able mirror respecti+ely. . It is ob+ious that the extra distance tra+elled by the light which stri1es the mo+able mirror is 2>. The extra distance is defined as the optical path difference (;'9& and is represented by delta. Therefore δ ?2@
It is well established that when ;'9 is the multiples of the wa+elength constructi+e interference occurs because crests o+erlap with crests troughs with troughs. As a result a maximum intensity signal is obser+ed by the detector. This situation can be described by the following e8uation δ ?nλ
(n ? %023...& In contrast when ;'9 is the half wa+elength or half wa+elength add multiples of wa+elength destructi+e interference occurs because crests o+erlap with troughs. onse8uently a minimum intensity signal is obser+ed by the detector. This situation can be described by the following e8uation δ ?(n02& λ
(n ? %023...&
These two situations are two extreme situations. If the ;'9 is neither n"fold wa+elengths nor (n0/2&"fold wa+elengths the interference should be between constructi+e and destructi+e. So the intensity of the signal should be between maximum
and minimum. Since the mirror mo+es bac1 and forth the intensity of the signal increases and decreases which gi+es rise to a cosine wa+e. The plot is defined as an interferogram.
Figure 0.% A typical FTI! *ac1ground Spectrum.
4. Examine the salicylic acid spectrum. Using the structure of salicylic acid, identify the major peaks in the spectrum.
Table 1 : Typical nfrared !bsorption "re#uencies
"igure $: %olecular structure of &alicylic acid. "rom the graph of the infrared analysis of salicylic acid, the peaks from the graph are sho'n belo' and their functional group based from table 1 (4)*.1( : +- alcohol functional group/ • (410.1 : +- alcohol functional group/ • ($(2.)( : +- alcohol functional group/ • (*11.() : +- carboxylic acid/ • $02. : +- carboxylic acid/ • 1)3.4) : 5 alkenes/ • 1$1.* : 5 alkenes/ • 1)33.$ : 5+ • 1)($.2 : 5+ • 133$.*4 : 5+ • 131$.32 : 5+ • 1020.2) : 5 • 144(.04 : 5 • 14)1.2* : 5 • 1$3.2( : + • 1$40.23 : + phenol/ • 1$*.*( : + phenol/ • 110$.10 : + phenol/ • 1*$).0) : + phenol/ • 33.$$ : 5• )1.$3 : • 20).42 : +- 'eak bond/ • 34.20 : • 303.44 : • The major peaks in the spectrum for salicylic acid can be determined by the bonds 'hich are + - 'ith range of around (0** to $0** follo'ed by 5+ 'ith range of 1)** to 13**. The range for 5+ is not accurate due to impurities 'ithin the samples.
0. Examine the commercial aspirin spectrum and determine spectral contributions from salicylic acid.
"igure ( : %olecular &tructure of !spirin "rom the graph of the infrared analysis of aspirin, the peaks from the graph are sho'n belo' and their functional group based from table 1 • • • • • • • • • • • • • • • • • • • • • • • • • •
The spectral contributions of aspirin from salicylic acid based on the spectrum analysis are the
+- and 5+ bond. !ll the bonds identified are taken in approximation to their respecti6e fre#uency due to impurities in the sample 'hile conducting the experiment.
