Lab 11 Flashcards
Describe the results of the iron(III) chloride tests. What do the results indicate about your product? Explain your answer.
These results indicate that my final product was not completely pure. Salicylic acid has a phenol group and therefore the iron cation forms a complex with a phenolic oxygen atom. Therefore, the purity is represented based on how purple the solution turns, the darker the solution the more salicylic acid present, thus creating an impure solution. The salicylic acid solution was a deep purple in color and the commercial aspirin was faint purple in color indicating that salicylic acid was present. Before crystallization our product was a transparent light purple, indicating that the product contained salicylic acid. There was not a complete conversion of reactants to products therefore a recrystallization had to occur. After the recrystallization process our product achieved a light purple color indicating that salicylic acid was present, but the product was more pure.
- What was the purpose of adding water carefully at the end of the reaction? Write an equation for the reaction involving the water.
The purpose of adding water at the end of the reaction was to decompose the excess acetic anhydride to form acetic acid. We did this because acetic acid is water soluble.
C4H6O3 (l) + H2O(l) → 2 CH3COOH(aq)
Explain why acetic acid is unlikely to be a contaminant in your solid aspirin.
Acetic acid is unlikely to be a contaminant in our solid aspirin because it is water soluble. Furthermore, the water soluble acetic acid will be removed using vacuum filtration. Vacuum filtration uses a lot of water, therefore the acetic acid would be dissolved. In this experiment we used vacuum filtration many times which also ensured the acetic acid would be an unlikely contaminant in our solid aspirin.
Aspirin tablets that have been stored for a long time may have a vinegar-like odor and give a purple colour with FeCl3. What reaction would cause this to happen?
C7H6O3(s) + CH3COOH(l) ⇌ C9H8O4 (s) + H2O(l)
Salicylic acid and acetic acid form acetylsalicylic acid (aspirin) and water. If aspirin tablets have been stored for a long time they may have a vinegar-like odor and give a purple colour with FeCl3. This is because the older the tablets get the more likely they are to absorb moisture from the environment and go in the reactions reverse direction (than the one shown above). Therefore, acetic acid (vinegar) will cause the vinegar- like odor and salicylic acid will cause the solution to turn purple when mixed with FeCl3.
Silica is polar and the mobile phase is less polar. Which is the most polar analyte of the tested compounds? Explain.
Silica is a polar compound, therefore nonpolar compounds move higher up on the silica plate as they are less polar. My results indicated that caffeine is the most polar analyte of the tested compounds. This is because the TLC analysis represented that caffeine barely moves up the silica plate. Furthermore, aspirin was the most nonpolar compound as it moved the highest up the silica plate.
