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How do we know?

  1. Jun 22, 2010 #1
    Is there any other way (besides experimentation) to know what chemicals react with other chemicals? Take this http://oxygen.chem.uidaho.edu/dschem276/Laboratory Experiments/Caffeine extraction from Coffee.pdf" for example, is there any other way to know that caffeine is soluble in water? And that tannin is NOT soluble in chloroform, but caffeine is?

    Why would you have to heat the solution with the caffeine and the tannin in it in order for the caffeine to become soluble?
    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Jun 23, 2010 #2


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    Staff: Mentor

    Yes. No.

    Usually looking at the substance structure we can predict whether we should expect to dissolve in polar or non polar solvents, but reality has its own ways and sometimes our predictions are wrong. Experiment is the only 100% sure way of getting the answer.

    It doesn't state tannin is not soluble in chloroform. It states that tannin reacts with carbonate to create a salt which is insoluble. That's nothing unusual - in general ionic salts are weakly soluble in non polar solvents, that's one of rules of thumb used to predict solubility.

    Solubility of most substances goes up with the temperature, counter examples do exist, but they are rare. It doesn't mean caffeine is insoluble in cold water - just its solubility is lover and dissolution is slow.

    Last edited by a moderator: Apr 25, 2017
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