Aspirin SAC

[tony3272]

Btw when you're commenting on the purity of the sample, are you just looking at your percentage yield?

[jasoN-]

yield doesn't really say much about purity,
i guess the best way is to measure the melting point, and if its considerably below the range (i think~138 is the expected of pure aspirin) then its impure (mainly due to the presence of water)
however idk if you guys measure melting point in ur labs

[tony3272]

Ah okay that makes sense. I highly doubt we'll do something like that.

[eeps]

I did the Aspirin SAC last week. The actual prac questions may vary slightly from school to school, but some of the questions I had to answer were:
- What's the purpose of adding Sulfuric acid?
- Why is water added at the end of the reaction?

Go on, give us some answers

1. Acts as a catalyst; as mentioned previously.
2. Allows for crystallization to occur and to cool down the sample.

Btw when you're commenting on the purity of the sample, are you just looking at your percentage yield?

No. It was something to do with the reaction; if the sample didn't change colour, then that would mean there is a higher purity in the sample. I can't remember my exact answer. It will make more sense when you do the prac. Good luck!

[DisaFear]

What is the purpose of recrystallisation? (if you guys did that)

[jane1234]

What is the purpose of recrystallisation? (if you guys did that)

To purify the aspirin sample by getting rid of the other chemicals that were involved in the synthesis process.

[jackson1234]

I did the Aspirin SAC last week. The actual prac questions may vary slightly from school to school, but some of the questions I had to answer were:
- What's the purpose of adding Sulfuric acid?
- Why is water added at the end of the reaction?

Go on, give us some answers

The purpose of adding sulfuric acid is because esterification occurs ideally under acidic environments (it's a catalyst)

Limiting agent would be the salcylic acid

Cold water is used to lower the solubility of aspirin ( as with all precipitates, there is still a minor chance of them dissolving in water ). Water is also used to rinse and to ensure that other solubles and reactants are washed away.

Purity of sample -  Just comment on things that can cause your aspirin sample to be contaminated. You could mention that a ferric chloride test may be used to assess the purity of the sample, or simply use something like TLC [ one dot - pure, two dots- impure ]

[tony3272]

Just a quick question. What would happen if not enough sulfuric acid was used? Because i spilled a bit on my hand today (LOL) and forgot to refill the amount that was lost.

[jane1234]

Ouch didn't that hurt? I don't think it would do anything as it only acts as a catalyst, but you never know...

[tony3272]

It did a little bit, but it wasn't too bad. I was thinking that it would have some slight effect on the yield, such as if the aspirin wasn't fully able to precipitate.

[homosapiens]

If salicylic acid is the limiting reactant, is it possible for some to be left? ie the sample turns purple when adding Fe(NO3)3? Is this due to not scratching it mixture properly?

[jane1234]

If salicylic acid is the limiting reactant, is it possible for some to be left? ie the sample turns purple when adding Fe(NO3)3? Is this due to not scratching it mixture properly?

Yes, because the reaction will not go to completion and there will be some of the reactants left as well as the products and catalysts in the final solution.