|
We prepared aspirin as a lab on friday, and I have one question I'm unsure of. ASA is made from salicylic acid and acetic anhydride.
Q. The acidic charatcer of ASA may be used to quantify the amount of pure ASA in a sample. Suggest a procedure that may be preformed in a school labratory to test the purity of the ASA sample you prepared based on the knowledge of acids and bases. Shows materials, how the results may be interpreted, safety precautions, ect.
Note: ASA is just a short form for aspirin, if you were wondering. I'm going to review the acid/base section of my text and try to find something to go with. Thx in advance.
EDIT: Oh, and this is how we made the ASA...
1. 4g of salicylic acid in a flask
2. Added 8mL of acetic anhydride (stirred till solids dissolved)
3. Added 4 drops sulfuric acid
4. Placed contents within flask into a hot water bath for 15 min
5. Added to ice water bath and stirred for 10 min
6. Put contents in a filter paper, and let it dry overnight.
|
Something along the line of Ka...
So if it's pure ASA acid, it has a certain Ka value.
Note:
Ka = [H+]*[some conj base]/[Hbase]
so w/ ASA, you know the Ka value. and if it's not pure ASA, the Ka value should be different.
Compare the 2 Ka value for the answer. I think.
However, it's not really reliable, what if the other stuff has the same Ka or simular to that of ASA?
I'd really suggest instead of using the acidity procedure to find the purity, you'd rather:
Do a standardized synthesis, record all datas.
Now you have a sample, measure it's mass, and compare it to the stoichometric mass, it should be more accurate that way.
Or just eat it and see if it ease ur headache >
|
|
|
What I've found is that you could:
Test the product for relative purity as follows. Place a few crystals of salicylic acid in one test tube; in a second, place a little crushed commercial aspirin; in the third test tube, add a few crystals of your prepared acetylsalicylic acid. Now add a few drops of iron(III) chloride to each tube and shake to mix the contents.
The SA should turn dark purple; the prepared sample should be dark purple (due to SA contamination), and the commercial aspirin sample will probably be a pale orange color (indicating no SA contamination).
Many phenols (R-OH) produce colored coordination compounds with iron(III) ions. These complex anions are composed of 6 molecules of the phenol combined with one iron(III) atom. Since salicylic acid has a phenolic –OH group, it produces the positive (purple) test with iron(III) chloride.When SA reacts completely to produce ASA, the phenolic group is replaced with an acetate (acetyl) group, so the iron test would be negative. Of course, students will not get 100% yield, so some SA remains to make their sample purple in the iron test.
|
On June 18 2006 16:18 nortorius wrote:
What I've found (<3 google) is that you could:
Test the product for relative purity as follows. Place a few crystals of salicylic acid in one test tube; in a second, place a little crushed commercial aspirin; in the third test tube, add a few crystals of your prepared acetylsalicylic acid. Now add a few drops of iron(III) chloride to each tube and shake to mix the contents.
But it doesn't say what should happen in each scenario & why.
lol it's obvious that ur bm if you turned that in though :O
|
I know, don't plan to use it, but it could assist. Reviewing the acid/base section will probably give me the best results, but if I cannot find anything relevant to the question I will have to think of something else.
|
Seems like the best bet is doing an acid-base titration w/ standardized NaOH as the titrant, and the ASA (obviously) as the sample (diluted in 50mL of water). Once the equivalence point is found, the C1V1 = C2V2 formula can be used to determine the concentration of salicylic acid, and thus it will show if the aspirin is pure or not (based on percentage yield). Yeah.
|
okay
|
rofl, I did this lab a week or two ago in my chem class - don't remember much about it though since im focusing more on my exams
|
help me i need a good reasonable answer
|
Aspirin is a strong acid so titration with NaOH or KOH should work fine. The iron test could work but that is obviously not what is asked since they emphasized acid base properties. Also, it's not quantitative. If you are really lazy you could make a solution in water and test the pH to compare with the theoretical value. However, that's not very precise in my opinion.
|
|
|
|
|
|
EPT
