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State of matter in chemical reaction

  1. May 12, 2015 #1
    Does anybody know where I could find worksheet to practice naming the state of matter in chemical reactions (with answers in the worksheet to check) as I have problems with that. Especially deciding when it is aqueous. I know (well at least i am right) that when you have acid as reactants it has to be aqueous if you get water as product. But how do you decide for other? Is there any rule?(well, most likely is but I did not find it).
    Thanks
     
  2. jcsd
  3. May 12, 2015 #2

    James Pelezo

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    Your question sounds like you are struggling with double replacement reactions (i.e, metathesis reactions). AX + BY => AY + BX ... These are governed by solubility rules of ionic compounds and formation of weak electrolytes. If this sounds like what you need, let me know and I'll try to help. If not, elaborate a little more on the reaction types that are giving you problems. I don't want to overburden this reply with too much of what you don't need.
     
  4. May 12, 2015 #3
    This sound exactly right. So, if you know the solubility then you can determine if it's aq, right?
     
  5. May 13, 2015 #4

    James Pelezo

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    OK, then ... here's a little more on the subject to get you started...
    1. Metathesis reactions are divided into 3 classes based on the driving force of the reaction. That is, which of the product compounds in a double replacement pulls (so to speak) the reaction to completion. These are reactions driven by formation of an insoluble precipitant, formation of a weak electrolyte or formation of a gas decomposition product. The object of the driving force is to prevent the reactions from reversing. Once the driving force is identified, the remaining components/compounds of the reaction are in aqueous phase.

    2. Let's start with the precipitation reactions.
    a. AX + BY => AY + BX ... AX and BY are both salts or metallic hydroxides that are considered to be 100% ionized. So, both reactants in this class of rxn are ALWAYS in aqueous phase, meaning they are 100% ionized. Now, one of the products must be the driving force (insoluble ppt (solid)) but the other will not ppt and remain in ionic form and thus be aqueous. So now the question is, how do you identify which one of the products is an insoluble precipitant? You need to learn the solubility rules of ionic salts and insoluble (or, very low solubility) hydroxides. Once you know which will ppt, tag it with (s) and all others with (aq).

    b. So, what are the solubility rules that define ppt driving force compounds? Always keep in mind that you are looking on the product side of the reaction for the driving force, regardless of class. In this class, a salt or hydroxide with an extremely low solubility. Memorize the following.

    Halide Salts of Mercury, Silver and Lead. All other halides are soluble and NOT driving force compounds.
    Sulfate Salts of Barium, Strontium, Calcium & Lead. All other Sulfate salts are soluble and NOT driving force compounds.
    Metallic Hydroxides EXCEPT for Group IA Hydroxides
    Phosphate Salts EXCEPT for Group IA Phosphates
    Carbonates EXCEPT for Group IA Carbonates
    Sulfides EXCEPT for Group IA Sulfides

    Per your initial request:
    Here's an example: http://www.chemunlimited.com/Metathesis Double Replacement Rxn - Ppt Dvg Force.pdf
    Here's a worksheet: http://www.chemunlimited.com/Metathesis Reactions Worksheet.pdf
    Here are the worksheet answers: http://www.chemunlimited.com/Metathesis Rxns Worksheet - Answers.pdf

    I'll post some more info on the second class of metathesis rxn tomorrow. Best of luck.
     
    Last edited: May 13, 2015
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