Double_Displacement_Reactions_ver_4.0 - Experiment Double...

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Experiment: Double Displacement Reactions Background Skills/Concepts Predicting double displacement reactions Writing molecular, ionic and net ionic equations Understanding the dissolution of ionic compounds in water Relevant Reading Brown & LeMay, Chemistry the Central Science: Chapter 4 Background A double displacement reaction involves two ionic compounds that are dissolved in water. In as double displacement reaction, it appears as though the ions are “trading places,” as in the following hypothetical reaction: AB (aq) + CD (aq) AD + CB Where AB exists as A + and B - ions in solution and CD exists as C + and D - in solution. As the ions come in contact with each other, there are six possible combinations that might conceivably cause a chemical reaction. Two of these combinations are the meeting of ions of like charge; that is A + and B - and C + and D - . But since like charges repel, no reaction will occur with these combinations. Two other possible combinations are those of the original two compounds; that is A + + B - and C + and D - . Since we originally had a solution containing each of these pairs of ions, they can mutually exist in the same solution; therefore they do not recombine. Thus, the two possibilities for chemical reaction are the combination of each of the positive ions with the negative ion of the other compound; that is, A + + D - and C + + B - . In summary, when the solutions are mixed, these ions can all come into contact with each other, and new product could be formed. If new products are to be formed, there is only one possible combination of products: since like charges repel each other, we cannot have new compounds containing two negative ions or two positive ions. The only other possible new combination comes from the positive and negative ions of the two compounds switching places. There are three types of equations that can be written for reactions that involve ions in solution. The first type is the “molecular” equation. An example of this is shown for the following double displacement reaction:
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2 Double Displacement Reactions Cañada Chemistry Department Version 4.0 Na 2 CO 3(aq) + 2AgNO 3(aq) 2NaNO 3(aq) + Ag 2 CO 3(s) In this type of equation the complete formulas are shown along with the appropriate state symbols. The formulas of the products are obtained as follows: 1) Determine what ions are present in the reactants, without worrying about how many of each there are. Include their charges: Na + , CO 3 2- , Ag + , and NO 3 -1 . 2) Switch the ions so that the cation of the first compound is paired with the anion of the second compound, and vice versa. In this case, the Na + is paired with the NO 3 -1 and the Ag + is paired with the CO 3 2- . 3) Determine the correct formulas of the products, keeping in mind the charges on each of the ions and
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Double_Displacement_Reactions_ver_4.0 - Experiment Double...

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