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Thread: Assigning states in reactions

  1. #1 Assigning states in reactions 
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    How do I determine whether the products of a reaction are (s), (l), (g), or (aq)?

    For example in the equation,

    AgNO3 + KBr -> AgBr + KNO3

    (correct the equation if I didn't do it right...)

    Thanks.


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  3. #2 Re: Assigning states in reactions 
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    Quote Originally Posted by brushman
    How do I determine whether the products of a reaction are (s), (l), (g), or (aq)?

    For example in the equation,

    AgNO3 + KBr -> AgBr + KNO3

    (correct the equation if I didn't do it right...)

    Thanks.
    Well, for the reactants, you really can't without knowing in advance (as far as I know anyway). But you can narrow it down. For a double replacement reaction, things have to be in either aqueous, and I think liquid and gaseous might also be acceptable forms, but I'm not sure about that. It's highly unlikely that you have molten salts of AgNO3 or KBr. They're almost always aqueous.

    For the products, refer to a solubility table for the ions. For example, KNO3 is soluble because group 1 ions are always soluble and nitrate is always soluble (in water anyway). The silver bromide HAS to leave the solution either as a gas (not happening), a precipitate, or create water (not happening). This does indeed happen because halide ions are insoluble when combined with silver.

    Google: Chemistry Reference Table. It's the NY State table that's given to high school chemistry students. I've used it and it's quite good. For this purpose, you want the old version, I think the chart was much more complete.


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  4. #3  
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    Trick question! your starting materials are solid salts in their normal state, you produts are also, BUT the reaction has to take place in H2O solution. The KNO3 is soluble, the AgBr is not and ppts. out.
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  5. #4  
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    Thanks for the replies, but I'm still kind've confused.

    The way I understand it is this reaction occurs IN water. Is this right?

    Google: Chemistry Reference Table. It's the NY State table that's given to high school chemistry students.
    I looked at this and "E" seems to be what I'm looking for. How would I use this table? If it's soluble does that mean it's (aq)? And if it's insoluble does that mean it's (s), (l), or (g)? What about the ones that are only slightly soluble?

    What about "solubility rules", such as these I found http://boomeria.org/chemlectures/textass2/tableA-7.jpg

    Basically I use it the same way as the table?

    Thanks
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  6. #5  
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    Quote Originally Posted by brushman
    I looked at this and "E" seems to be what I'm looking for. How would I use this table? If it's soluble does that mean it's (aq)? And if it's insoluble does that mean it's (s), (l), or (g)? What about the ones that are only slightly soluble?

    What about "solubility rules", such as these I found http://boomeria.org/chemlectures/textass2/tableA-7.jpg

    Basically I use it the same way as the table?

    Thanks
    If you're using the old version and it has the degrees of solubility listed, slightly soluble should still be (aq). As long as the table makes a distinction between insoluble and slightly soluble (I forget if it does), you can treat slightly soluble as soluble. If not, I'd count it as insoluble. The new version is more clear-cut with that and just tells you whether or not the substance is soluble. Soluble substances appear as (aq) and insoluble ones appear as s/l/g.

    Those "solubility rules" you found appear in the new version of NY State's Chemistry Reference Table in a much cleaner-presented manner. It's also more in-depth. Check out the new reference table. It may be better for you, since it looks like you just need to know if a substance will precipitate or stay in solution.
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