General Chemistry w/Lab I
Experiment: The Nine Solution Problem
In this laboratory you will be provided with a set of nine solutions. Unfortunately, the labels have fallen off the bottles! It will be your task to identify the contents of each bottle. Part of your grade will be based on the correct identification of each.
An important class of chemical reactions is double replacement, or metathesis, reactions. These occur when aqueous ionic compounds combine by trading or replacing ions. For example, in the following double replacement reaction:
3 AgNO3 (aq) + Na3PO4 (aq) > Ag3PO4 (s) + 3 NaNO3 (aq)
you can see that the ions have traded places. The cation from the first compound forms a compound with the anion from the second compound and vice versa. In a double replacement reaction one of the products is frequently insoluble and appears as a precipitate. In the case of the reaction above a precipitate of solid silver phosphate forms.
Because the reaction takes place in solution it is often appropriate to write the reaction in ionic or net ionic form. When ionic compounds are in solution, those compounds that are soluble will dissociate into ions; compounds that are insoluble do not dissociate. You will need to consult your text (p. 145 & Appendix C, p. A13) or a reference book to determine which compounds are soluble and which are insoluble. In the double replacement reaction above, both of the reactants are soluble, while one of the products is insoluble and the other is soluble. Thus, the ionic equation for this reaction is best written as:
3 Ag+ (aq) + 3 NO3- (aq) + 3 Na+ (aq) + PO4-3 (aq) > Ag3PO4 (s) + 3 Na+ (aq) + 3 NO3- (aq)
In this example, the compounds which are soluble in water (AgNO3, Na3PO4 and NaNO3) have been shown dissociated into ions. This is how these compounds would actually exist in solution.
The net ionic equation is similar, but removes clutter in the reaction by canceling out those substances which appear on both sides of the equation. These are called spectator ions; they have not undergone any chemical change. Thus, the net ionic equation for this reaction would be:
3 Ag+ (aq) + PO4-3 (aq) > Ag3PO4 (s)
This equation shows only those substances which are undergoing chemical change. The spectator ions, Na+ and NO3-, have been removed.
In this lab you will work with the following nine solutions:
You are to mix each solution with each of the others, and determine whether the ions have combined to form new substances. You will be able to determine if a reaction has occurred if you observe one of the following:
In this laboratory you will work with your lab partner to complete the following:
Analysis and Report
Be sure to include the following in your laboratory report:
Your identification of the nine solutions must follow from your experimental data. You will lose points if you give results which are not supported by your data and reasoning.
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