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Solubility Rule Question

  1. Mar 24, 2015 #1
    1. The problem statement, all variables and given/known data
    Ok, so basically, our teacher gave us some solubility rules... then we did a problem where we mixed two solutions and checked to see if a precipitate would form.

    So he calculated Qsp for one of the products and compared it to Ksp for that product, he did not calculate Qsp and Ksp and forth 'other'... this 'other' product obeyed the solubility rules.

    So from what I understand, when you mix two solutions to see if a precipitate forms, you ignore the soluble products because they have infinite solubility?

    I mean, do the solubility rules tell us that those substances have infinite solubility?
  2. jcsd
  3. Mar 24, 2015 #2

    Quantum Defect

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    Nothing has infinite solubility.

    If you look in tables (like in the CRC Handbook) you will see solubility data given, units will be something like grams per kg water, or grams per liter.
  4. Mar 25, 2015 #3


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    In a way infinite solubility is miscibility. But its not about solids dissolved in liquids, but about liquids dissolved in liquids.
  5. Mar 26, 2015 #4
    Ok. So infinite solubility doesn't exist, but in the original case mentioned, we ignore the soluble substance because its just way more soluble, correct?
  6. Mar 26, 2015 #5

    Quantum Defect

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    Na+ salts are very soluble, nitrates are soluble, ... Some things are very soluble, many things are insoluble. Generally when you are trying to mix two liquids together, you will have an anion paired with something like sodium cation and a cation paired with something like nitrate. Mixing the two will give you e.g. "sodium nitrate" as one candidate for froming a precipitate (it won't because it si really soluble) and another candidate -- e.g. AgCl (like if you mixed silver nitrate with sodium chloride). As you do more of these things you will learn to recognize the likely culprit from the innocent bystander -- like any good detective!
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