ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: tony3272 on May 21, 2011, 09:33:45 pm
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I have my aspirin sac this thursday(or friday?). We're basically just preparing aspirin and then doing a mini write up with some questions for the discussion in the same lesson. Since it's supposed to be a suprise for us when we ge there, we have no details about the sac except what i've just stated.
So I was just wondering;
Is there any way we can prepare aspirin besides reacting salicylic acid with ethanoic anhydride?
And also, is there a lot theory-wise that would we would generally need to know about this?
Thanks guys :smitten:
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Well the prac is pretty straight forward, i.e. theres not much to it.
Just revise the theory related to the creation of aspirin especially the bonding aspects to it. Be familiar with molecular formulas and questions like ... " why is cold water used" . You could use ethanoic acid to prepare aspirin, but i doubt it would be used as it leads to a lower yield (water may react back through hydrolysis) and the reaction is relatively slow.
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Well the prac is pretty straight forward, i.e. theres not much to it.
Just revise the theory related to the creation of aspirin especially the bonding aspects to it. Be familiar with molecular formulas and questions like ... " why is cold water used" . You could use ethanoic acid to prepare aspirin, but i doubt it would be used as it leads to a lower yield (water may react back through hydrolysis) and the reaction is relatively slow.
Ah okay thanks. Thats good then :D
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Other than ethanoic anhydride, you can use ethanoic acid :) the only thing is though the percentage yield is likely to be less and you have a by-product (water) whereas if you use ethanoic anhydride, your by-product would be ethanoic acid and you could reuse that to make ethanoic anhydride :)
Just saying :)
Good luck!
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How would you show that the sulfuric acid is a catalyst and not a reactant in this prac?
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How would you show that the sulfuric acid is a catalyst and not a reactant in this prac?
You would perform two reactions - one using the sulfuric acid, the other not using it. You would time then and see if the one with the H2SO4 would react quicker.
Goodluck on your SAC :)
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How would you show that the sulfuric acid is a catalyst and not a reactant in this prac?
You would perform two reactions - one using the sulfuric acid, the other not using it. You would time then and see if the one with the H2SO4 would react quicker.
Goodluck on your SAC :)
Ah that's simple :) Thanks
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We have our aspirin sac write-up tommorow, I could give you our questions, if you wanted to answer them, the prac questions (I assume that isn't illegal, aye, just sharing questions)
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We have our aspirin sac write-up tommorow, I could give you our questions, if you wanted to answer them, the prac questions (I assume that isn't illegal, aye, just sharing questions)
Haha ours is thursday. Have you already done the prac?
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Yep, write-up is tommorow
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Yep, write-up is tommorow
Oh ours is weird since we do the prac and write up in the same day.
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Ours was a 4 day process
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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:
- Draw the full structure of the Aspirin reaction.
- Circle the functional groups in Salicylic acid.
- What's the purpose of adding Sulfuric acid?
- What is the limiting reagent in the reaction?
- Why is water added at the end of the reaction?
- What’s the theoretical yield of the Aspirin? You're given figures for this question.
- Comment on the purity of the sample.
My SAC had about 15 theory-based questions - quite long; the actual prac itself isn't that hard. Good luck.
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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 :D
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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:
- Draw the full structure of the Aspirin reaction.
- Circle the functional groups in Salicylic acid.
- What's the purpose of adding Sulfuric acid?
- What is the limiting reagent in the reaction?
- Why is water added at the end of the reaction?
- What’s the theoretical yield of the Aspirin? You're given figures for this question.
- Comment on the purity of the sample.
My SAC had about 15 theory-based questions - quite long; the actual prac itself isn't that hard. Good luck.
Oh wow nice. That doesn't seem to bad.
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Btw when you're commenting on the purity of the sample, are you just looking at your percentage yield?
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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
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Ah okay that makes sense. I highly doubt we'll do something like that.
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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 :D
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!
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What is the purpose of recrystallisation? (if you guys did that)
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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.
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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 :D
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 ]
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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.
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Ouch didn't that hurt? I don't think it would do anything as it only acts as a catalyst, but you never know...
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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.
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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?
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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.