| Double displacement reactions are of the type:
AB + CD à AD + BC In the reactions we will study, each of the compounds will form ions in solution, then the ions will recombine to form new compounds, or remain in solution. In today's experiment you win perform the reaction, observe the results, then test known compounds and design further experiments using these known compounds to test your hypotheses about what has occurred. If you see no visible signs of reaction, such as a temperature change, a precipitate being formed, or a gas being released, it may be that the compounds have simply dissolved in solution without recombining. If you feel this is the case, simply write "no reaction", however you must justify this conclusion. An example of a double displacement reaction is the following: NaCI + AgNO3 à NaNO3 + AgCl |
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When solutions of the two reactants are combined, a white precipitate
is formed. This is definite evidence that a reaction has occurred. In this
reaction, sodium chloride dissolves in solution to form sodium ions Na+
and chloride ions (Cl-) Silver nitrate dissolves to give silver ions (Ag+)
plus nitrate ions (NO3- ). These ions recombine to form the products as
shown in the reaction. How can you tell which product or if both are the
white precipitate? One way would be to take a small amount of sodium nitrate
(NaNO3) and see if it dissolves in water. If it does, you can rule it out
as the product that precipitated. Likewise you could see if silver chloride
dissolves in water. If you did these experiments you would find that NaNO3
does indeed dissolve in water whereas AgCl does not. You would conclude
that the white precipitate formed was AgCl Another way to determine this
would be to look at a table of solubilities such as the one provided below.
This will help to you determine which of the proposed products is the precipitate.
From the table, we see that NaNO3 is soluble, and AgCl is not in water
solution, just as we had found out from our experiments.
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| Another example is the reaction of sodium hydroxide solution with hydrochloric
acid:
NaOH + HCl à NaCl + H20 The only evidence of a reaction having occurred is a temperature change. The reaction vessel feels warm to the touch. This heat is released when water forms from the hydroxide ion (OH-) and the proton (H+) |
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| In today's experiment you will combine reactants, notice any results of reaction, and determine what reaction has occurred if any by looking at the table of solubilities provided and/or observing and testing known compounds from the laboratory. |
| 1. Take a test tube of the size you will be using in today's experiment and add to it 3 ml of water. Use this as a calibration device. |
| 2. Mark the other test tubes you will be using to this mark. Now add another 3 mls of water to the first tube. Again mark the tubes you will be using so that each now will have a mark representing 3 ml and 6 mls. |
| 3. Add each solution in 3 ml quantities. |
| 4. Use a clean test tube for each experiment. |
| 5. Make a table in your lab notebook having a column for the reaction which has occurred (or "no reaction), and a column for your observations and further experiments or evidence for your conclusions (leave substantial space for each entry). |
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| 1.)0.1 M sodium chloride and 0.1 M potassium nitrate solutions. |
| 2.)0.1 M sodium chloride and 0.1 M silver nitrate solutions. |
| 3.)0.1 M sodium carbonate and concentrated (12 M) hydrochloric acid solutions. |
| 4.)10% sodium hydroxide and 6 M hydrochloric acid solutions. |
| 5.)6 M ammonium hydroxide and 3 M sulfuric acid solutions |
| 6.)0.1 M barium chloride and 3 M sulfuric acid solutions. |
| 7.)0.1 M copper(II) sulfate and 0.1 M ammonium chloride solutions. |
| 8.)0.1 M sodium carbonate and 0.1 M calcium chloride solutions. |
| 9.)0.1 M iron(III) chloride and 6 M ammonium hydroxide solutions. |
| 10.)10 % sodium hydroxide and 6 M nitric acid solutions. |
| 11.) 0.1 M copper(II) sulfate and 0.1 M zinc nitrate solutions. |
2.) Write the ions for the compounds listed in the previous question.