Uploaded by Eliza Hanson

DSC Analysis of the Melting Point of Aspirin

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Name: Eliza Hanson
Lab Partners: Janae Peterson and Jessica Szuba
Date: March, April
Title: Differential Scanning Calorimetry
Purpose: To calibrate and standardize measurements on a differential scanning calorimeter, and
use that to precisely measure melting point and specific heat capacity of a sample of aspirin
Background: DSC is a type of highly precise thermal analysis, which can be used to
quantitatively and qualitatively understand and characterize a chemical sample. It is the most
widely used thermal analysis technique with polymers and organic materials, as well as being
useful for a variety of inorganic substances as well (such as indium metal or sapphire). (Source:
TA Instruments Modulated DSC Compendium)
Theory:
Specific Heat –
𝐸 π›₯𝐻
𝐢𝑝 = 60
π‘₯
π»π‘Ÿ π‘š
Cp=specific heat [J/g℃]
E = cell calibration coefficient
Hr = Heating rate [℃/min]
Ξ”H = difference in y-axis deflection between sample and blank curves at temperature of interest
[mW]
m = sample mass
Equipment list:
Differential Scanning Calorimeter (2010 DSC V4.4E)
TA Universal Analysis software
Excel
Standardized aluminum pans
Analytical balance
Petri dish for measurement/ sample protection
Flash drive to store data
Chem wipes
Pellet press
Sapphire standard
Indium Standard
Aspirin
Reagents:
Compound
Molecular
Formula
Sapphire
Al2O3
Indium
Indium metal
Aspirin
C9H8O4
Molecule
Structure
Molecular
Weight
MP or BP
Density (g/cm3)
MSDS
Indium metal
101.961
MP: 2030-2045℃
114.818
180.157
156.6℃
7.31 g/cm3
Dust may irritate
eyes, flammable
136-140℃
1.3 ± 0.1 g/cm3
Dust may cause irritation;
Irritate skin and
excessive ingestion harmful
eyes, harmful if
swallowed in
excess
All chemical data taken from chemspider.com, owned by the Royal Society of Chemistry
Cp of sapphire at 330 K: 102.4290 + 38.749t – 15.912t2 + 2.628t3 βˆ’
Taken from NIST webbook.
3.01
𝑑2
Procedure:
Overall Objective: To perform a temperature calibration, a baseline test, a cell constant test, and
then to obtain the specific heat and melting point of aspirin.
Baseline:
1. Remove pans from cell and replace lids/glass bell cover
2. Check that purge has is connected and on. Choose the desired flow rate based on
environmental conditions. Here, N2 flow rate was 97.
3. Select the wizard and run test under the following conditions:
Begin at 50℃, heat at 10℃/min until 210℃
Calibration run/baseline
Sample size: 0 mg
Pan type: aluminum
4. Click apply to save parameters
5. Save file to known location
6. Select start (green arrow β€œplay” symbol)
7. Wait for test to conclude, and save data
8. Use TA universal analysis to plot curve of line.
9. Save data and analysis.
Temperature Calibration:
1. Prepare a sample pan containing approx. 10 mg of sample. For first run, choose a
material with a known melting point, such as Indium.
2. Place a reference pan (blank) on the back pan platform
3. Replace DSC lids and glass bell
4. Ensure that air flow is on
5. Set instrument for calibration mode, and choose temperature. Use a ramp method
6. Use the following settings:
Indium pan/ sample pan
Sample size: see results
Calibration/temperature calibration
Temperature range: 50-210℃
Heating rate: 10℃ /min
Cell constant:
1. Prepare a sample as in previous runs.
2. Settings:
Calibration/cell constant
Same temperature range and heating rate
Indium sample/ aspirin sample
Heat Capacity:
Note: for aspirin, this test must be run before melting point because aspirin will decompose.
1. Create baseline profile using empty sample and reference pans
2. Settings:
Conventional DSC/Ramp
50-210℃
Heating rate: 10℃ /min
3. Create a baseline run and hold starting temp for 5 minutes
4. Run a baseline run with a sample of known heat capacity
5. Super impose baseline graph 1 with sapphire graph, and measure change in y-axis heat
flow values.
Melting Point:
1. Run with the same parameters as the temperature calibration, this time with sample.
Results, experimental details, and data:
Trial 1: Baseline
Trial 2: Temperature Calibration
Trial 3: Cell Constant
Trial 4: Indium Heat Capacity
Trial 5: Aspirin Melting Point
Trial 6: Sapphire Specific Heat
Trial 7: Aspirin Specific Heat
Data transferred from DSC run, graphs generated in excel for ease of measurement and analysis
Calculations:
Melting point of Indium: 156.21℃
Percent error of Indium MP:
𝑒π‘₯𝑝𝑒𝑐𝑑𝑒𝑑 βˆ’ π‘šπ‘’π‘Žπ‘ π‘’π‘Ÿπ‘’
% πΈπ‘Ÿπ‘Ÿπ‘œπ‘Ÿ = |
|
𝑒π‘₯𝑝𝑒𝑐𝑑𝑒𝑑
156.6 βˆ’ 156.21
|
| = 0.24%
156.6
Melting point of Aspirin: 136.13 ℃
Percent error of Aspirin MP:
140 βˆ’ 136.13
|
| = 2.76%
140
Specific Heat of sapphire:
𝐸 π›₯𝐻
𝐢𝑝 = 60
π‘₯
π»π‘Ÿ π‘š
3.01
102.4290 + 38.749t – 15.911t2 + 2.628t3 βˆ’ 𝑑 2
Cp taken from 57℃ measurement
Cp(330K) = 92722617.7 J/mol = 9.272 * 10^7
𝐸
(3.19π‘šπ‘Š)
9.272 βˆ— 107 𝐽/π‘šπ‘œπ‘™ = 60
π‘₯
℃
22.9 π‘šπ‘”
(10
)
π‘šπ‘–π‘›
𝐢𝑝 = 60
𝐸 π›₯𝐻
π‘₯
π»π‘Ÿ π‘š
𝐸=
(9.272 βˆ— 107
𝐸=
𝐢𝑝 π‘šπ»π‘Ÿ
60βˆ†π»
𝐽
1 π‘šπ‘œπ‘™
𝐾
) (0.0229 𝑔 βˆ— 101.961 𝑔) (0.1667 𝑠 )
π‘šπ‘œπ‘™
𝐽
60(0.00319 𝑠)
E= 18137
Specific Heat of Aspirin:
𝐸 π›₯𝐻
π‘₯
π»π‘Ÿ π‘š
𝐽
0.001665
18137
𝑆
𝐢𝑝 = 60
π‘₯
𝐾
π‘šπ‘œπ‘™
0.1667 𝑠 0.0435 𝑔 βˆ—
180.157 𝑔
𝐢𝑝 = 60
Cp = 4.5*10^6J/mol
Discussion:
While there were errors in the DSC lab (someone lost the first indium standard, someone
misplaced our own blank, our aspirin was decomposed in the melting point test and thus we had
to obtain specific heat twice), we were ultimately able to find the data we were searching for. In
addition to finding specific heat of aspirin, we were able to find the melting point within 4
degrees of a common literature value. With % error values below 5%, this lab was fairly precise.
Conclusion: DSC is a highly useful analytical method to determine thermodynamic properties of
different compounds. The melting point determination was highly accurate, and it afforded the
ability to measure the specific heat capacity of aspirin. In the future, it would be an improvement
to run multiple tests on each compound, and it would be better to run the tests close together to
ensure that other parties didn’t change the DSC settings or move experiment materials. In
addition, a working knowledge of windows 98 would have helped immensely to curb the
learning curve on the analysis portion of the lab.
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