Take a good look at the product analysis procedure on page 7 of the Project 2B v
ID: 892445 • Letter: T
Question
Take a good look at the product analysis procedure on page 7 of the Project 2B v1.9 guide. Say you start with 0.152 g of crude ASA (impure aspirin) and you follow the procedure exactly, and obtain an absorbance at 517 nm of 0.858, what is the mass (g) of SA in the crude? Hint, you will need Beer’s Law and you must be mindful of the dilution in step 7.
Page 7 Procedure:
1) Weigh out 0.15x g of your crude ASA into a clean tared 7 mL (2-Dram) vial. Record exact mass of this crude sample.
2) Add 5 mL ethanol (this helps dissolve the crude). Break up any solid with spatula.
3) Cap vial and mix well.
4) Transfer the above solution into a 50 mL volumetric flask using a transfer pipette.
5) Fill your wash (squeeze) bottle with D.I. water. Use wash bottle to thoroughly rinse vial multiple times, transferring each rinse into the volumetric flask using the transfer pipette from step 4).
6) Bring flask volume to the 50.00 mL mark with D.I. water. Cap (or Parafilm™) and mix well.
7) Place 1.00 mL of this solution into a clean, dry 7 mL (2-Dram) vial. Add 3.00 mL 0.025 M Fe(NO3)3. Cap and mix well. This solution is stable for only 30 minutes – proceed quickly.
8) “Calibrate” spectrometer with D.I. water (NOTE: this may be different from what you did in Project 2A).
9) Fill cuvette 2/3 to 3/4 full with the solution from step 7). Wipe exterior of cuvette with a Kimwipe™.
10) Read the absorbance at 517 nm.
11) Determine the mass of SA in the crude sample analyzed (MM = 138.12 g/mol for salicylic acid and = 2147 M-1 cm-1 for the iron-salicylate complex, SA-Fe(H2O)4 + ). Be very careful with the volume! Notice the volume in step 6) and then the dilution in step 7).
12) From the SA mass and the total mass of the crude sample analyzed, you can find the approximate mass of ASA in the crude (approximate because you are assuming the amount of water, acetic acid and acetic anhydride present in the crude can be ignored). By calculating the percentage of ASA in the crude (by mass) you will have some measure by which to compare the ASA yield at different temperatures. Notice, you need to use the percent of ASA in the crude for this comparison and not the mass of ASA in the crude sample analyzed because the mass (amount) of crude sample will vary – by taking the percent (basically a ratio) you eliminate this complication.
my work:
M1/A1=M2/A2
.152/.858=X/138.12
.858x=20.99
X=24.468g
Please Help!!! Im not sure if I did this right.
Explanation / Answer
First of all, you started with .15 gm of crude material, you got answer 24.4 gm, which not correct.
To use beers law or beer lambert law, you need to provide all componet of equation like path lenth whic is missing here.
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