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how to contaminate pure aspirin help!!!! watch

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    hi,
    does anyone know how i could contaminate pure aspirin, just slightly so that i could test it with my mthods. the reason why am doing this is so that i can see if my techniques, back titration, direct, ph and colorimetry are good enough to test with commercial aspirin.

    however whatever i contaminate the aspirin with cannot react with NAOH during hydrolysis other wie i will get mucked up results. my taecher the idiot doesn't know enough chemistry to help me.

    thank you
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    Sorry I'm not sure what you are asking...you want to contaminate the sample so that you can test the purity of the sample and the vaildity of your techniques, but you don't want to detect the contamination in your results?
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    Most drugs are mixed with inert fillers and only contain a smal quantity of the active pharmacological agent. It could be magnesium carbonate, magnesium phosphate, calcium sulphate etc.

    Look up 'manufacture of pharmaceuticals' and I'm sure you'll get some good ideas, or elser just have a browse in the medicine cabinet and see what those drugs have in them.
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    (Original post by EierVonSatan)
    Sorry I'm not sure what you are asking...you want to contaminate the sample so that you can test the purity of the sample and the vaildity of your techniques, but you don't want to detect the contamination in your results?

    eiervonsatan your right tt what i want but don't know how to

    basically what i want to do is test how relaible my techniques are in testing the purity of the aspirin tablets. so basically what i did was get some pure aspirin and hydrolysed it with 1M NaOH and water. then i was about to back titrate it with 1M HCl but the phenolphathalein indicator wouldn't change pink telling me that all teh sodium hydroxide was sued up by the aspirin. so what i want to do is slighly contaminate the aspirin so it isn't that pure. but i can't think of something i could add to the aspirin that wouldn't also react with naoh.

    can anyone else think of soemthing
    let me know
    thanks for the eply by the way.
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    On average there is less than 20% of pure aspirin per tablet depending on strength.

    Tablets are just made larger using safe fillers as said above.
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    You could use e.g. p-dimethoxybenzene. It's soluble in organic solvents but is essentially neutral and won't react with either acids or bases (which makes it very easy to extract from your mixture if you want to do so). Alternatively you could use caffeine, which won't react with bases but will react with acids. This has the added advantage of realism, since caffeine is often added to aspirin to enhance its function. (When also mixed with paracetamol it's often called 'Nurse Sykes' Powders' or Excedrin, and you can buy this cheaply in supermarkets/pharmacies.)
    You could actually use these commercial tablets for analysis if you wanted, for some extra fun - since removing paracetamol is trivial, as it isn't soluble in e.g. dichloromethane (although many inorganic salts aren't, so you may need to purify it afterwards). So you just dissolve everything else in CH2Cl2 and then suction filter off the paracetamol; then acidify the mixture (using excess aqueous HCl, for example), shake the mixture, use a separating funnel to split up the aqueous and organic layers. Retain the organic layer for later use. Use the aqueous layer, basify and extract in dichloromethane (or some other organic solvent), then use a rotary evaporator or something similar to get your caffeine out. Finally use the organic layer you saved later, basify it, separate and retain the aqueous layer (the organic layer will contain impurities, such as p-dimethoxybenzene etc.), and then acidify this aqueous layer + extract in dichloromethane. Evaporating the dichloromethane (on a rotary evaporator) will give you aspirin.
    Then you can dry off all the powders you get (on a high vacuum line, for example) and analyse them as appropriate. (You'll probably need to repeat this several times to get good results, but it's a very quick procedure, it shouldn't take more than a few hours.)

    It's a really simple experiment, but still quite exciting in a way.

    If you're just interested in aspirin content per unit mass though, wouldn't it be easier to determine this using a spectrometer? I imagine aspirin should have a characteristic UV/Vis spectral peak, which would make the problem very easy indeed (just use the Beer-Lambert law).
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    (Original post by Sinuhe)
    You could use e.g. p-dimethoxybenzene. It's soluble in organic solvents but is essentially neutral and won't react with either acids or bases (which makes it very easy to extract from your mixture if you want to do so). Alternatively you could use caffeine, which won't react with bases but will react with acids. This has the added advantage of realism, since caffeine is often added to aspirin to enhance its function. (When also mixed with paracetamol it's often called 'Nurse Sykes' Powders' or Excedrin, and you can buy this cheaply in supermarkets/pharmacies.)
    You could actually use these commercial tablets for analysis if you wanted, for some extra fun - since removing paracetamol is trivial, as it isn't soluble in e.g. dichloromethane (although many inorganic salts aren't, so you may need to purify it afterwards). So you just dissolve everything else in CH2Cl2 and then suction filter off the paracetamol; then acidify the mixture (using excess aqueous HCl, for example), shake the mixture, use a separating funnel to split up the aqueous and organic layers. Retain the organic layer for later use. Use the aqueous layer, basify and extract in dichloromethane (or some other organic solvent), then use a rotary evaporator or something similar to get your caffeine out. Finally use the organic layer you saved later, basify it, separate and retain the aqueous layer (the organic layer will contain impurities, such as p-dimethoxybenzene etc.), and then acidify this aqueous layer + extract in dichloromethane. Evaporating the dichloromethane (on a rotary evaporator) will give you aspirin.
    Then you can dry off all the powders you get (on a high vacuum line, for example) and analyse them as appropriate. (You'll probably need to repeat this several times to get good results, but it's a very quick procedure, it shouldn't take more than a few hours.)

    It's a really simple experiment, but still quite exciting in a way.

    If you're just interested in aspirin content per unit mass though, wouldn't it be easier to determine this using a spectrometer? I imagine aspirin should have a characteristic UV/Vis spectral peak, which would make the problem very easy indeed (just use the Beer-Lambert law).

    thanks for that it was useful. my teacher told me to mix it with sodium cholride so then the sodium won't react with the sodium hydroxide and i will be left with salicylic acid and sodium chloride. but i was wondering if u could tell me how can i extract the rest of the impurites and just have salicylic acid. also instead of using a uv/vis spectra am doing colorimetery because with that i can also use the beer lambert law thing

    thanks great suggestions. appreactiate them
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    (Original post by funkysocks23)
    thanks for that it was useful. my teacher told me to mix it with sodium cholride so then the sodium won't react with the sodium hydroxide and i will be left with salicylic acid and sodium chloride. but i was wondering if u could tell me how can i extract the rest of the impurites and just have salicylic acid. also instead of using a uv/vis spectra am doing colorimetery because with that i can also use the beer lambert law thing

    thanks great suggestions. appreactiate them
    Well, I'm guessing here, but I'd just wash your organic solution of aspirin with (cold?) water, made slightly acidic (by a mineral acid such as HCl, NOT an organic acid).
    So if you have your aspirin + NaCl dissolved in dichloromethane, you pour in your acidified water, shake, and use a separating funnel to remove the aqueous layer, and repeat a few times; then dry the solution over e.g. magnesium sulphate (which you then remove by suction filtration).
    Maybe it's even better if you have your organic phase in acetone, as NaCl is very poorly soluble in acetone (but aspirin isn't).

    If you've used excess NaOH though (I'm not sure what your experimental procedure is exactly), you'll get, as you say, salicylic acid rather than acetylsalicylic acid (i.e. BAC2 ester hydrolysis). But the same principle applies.

    Also, once you've removed dichloromethane/acetone (by evaporation, e.g. using a rotary evaporator), you could recrystallise the acid from warm water (~50-60 degrees) to purify it further.

    Ok, these are just a few ideas; you'll need to consider if and how they fit in your experimental technique - your teacher will probably be able to advise you better.
 
 
 
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