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Before watching this video, you should have read Experiment six in the manual on the indicated pages. Additionally, it would be beneficial to review the sections in your lecture text that cover writing balanced molecular, ionic, and net ionic equations for precipitation reactions, as this will be crucial for completing your report for this experiment.

The goal of this experiment is to identify the cation M of a metal nitrate unknown salt solution, where M could be one of the eight cations listed. Most experiments you have done and will do in the Chemistry 1210 laboratory focus on quantitative analysis, which involves determining some numerical value about an unknown. For example, you have determined the density of a solution, the yield of a reaction, and the molarity of a solution. These quantitative analyses involve recording numerical data like masses and volumes. However, this experiment is an example of qualitative analysis, which focuses on identifying ions in a solution—either cations or anions. In this case, we are trying to identify a cation by making qualitative observations about the solutions.

Qualitative observations differ from quantitative observations and include noting whether or not a precipitate is formed upon mixing two solutions, as well as the color, amount, and form of that precipitate. For instance, you might describe a precipitate as a thick yellow solid or note that no precipitate formed in a particular reaction. You will identify which of the eight possible cations is in your unknown nitrate salt solution by comparing your observations of the unknown to those of known cations reacting separately with a series of anions. This comparison should lead you to determine the identity of your unknown.

One critical qualitative observation to make is about the solubility of the products formed from mixing the cation and anion solutions. We will categorize these products as soluble salts (S), slightly soluble salts (SS), or insoluble salts (I). A soluble salt will be clear in solution, indicating that you can see through it, while a slightly soluble salt will cause some cloudiness without any solid settling to the bottom. It is important to note that cloudiness is considered a precipitate, even if it does not settle completely; this will impact how we write our equations. An insoluble salt will result in a reaction mixture that is opaque, with solid actually settling at the bottom of the test tube.

After describing some examples of these products, it is crucial to understand that there isn’t necessarily a right or wrong when it comes to the color or form of the precipitate you observe. It’s important how you describe it because you will identify your unknown by comparison with your known observations. If you identify an unknown solution's precipitate as yellow and fluffy, and the same descriptor applies to a known cation, you will compare both accordingly.

Next, we will go over the procedure for the experiment, starting with the data page in your lab manual. This page provides an overview of how the procedure will work. I’ve highlighted the eight known cations and the associated squares for you to record your observations about reactions with the anions listed at the top. In addition, you'll note the unknown solutions you'll be comparing, including your own and your partner’s.

You will label each square as S, SS, or I for soluble, slightly soluble, or insoluble. In cases where you find a precipitate (slightly soluble or insoluble), you must note the color and form of that precipitate. Remember that this data is crucial, and standard data recording rules apply, such as using pen for your observations. It's also important to note that you do not need to describe the colors of the solutions themselves; we focus solely on the precipitates.

As you read the procedure, you will find a set of eight labeled test tubes for each known cation, along with a test tube for your unknown. You will add one of the anions to all test tubes containing known or unknown cations, mix the solutions, and record your observations. This process will be repeated for each anion: starting with chloride, then bromide, iodide, carbonate, sulfate, hydroxide, and finally sulfide. Be mindful that the sulfide has a strong odor, requiring the use of a fume hood for ventilation.

It is also vital to note that the order of adding anions does not matter since available supplies may limit you in a laboratory setting. As you analyze the results from each set of test tubes, be sure to note which known cations match up with your unknown. It often helps to put check marks next to the boxes representing potential matches on your data page.

To prepare for the experiment, you'll set up your labeled test tubes alongside a reference test tube filled with deionized water. This will help you identify precipitates easily. Ensure that your labeling tape is secure and placed entirely around the test tubes, as not doing so may lead to labels coming off during the experiment.

You should also prepare a large waste beaker for disposing of your waste and a beaker filled with deionized water along with a glass rod for mixing the solutions between tests. When you start mixing solutions, you will add five drops of each metal cation solution to their respective labeled test tubes, and then five drops of your unknown to either test tube labeled "unknown 1" or "unknown 2." Your partner will do the same with their unknown.

You will then add one of the anion solutions to each test tube and mix carefully with the glass rod—remember to rinse the rod between each mixing to avoid contamination. Take care to look closely at each reaction and record your observations accurately.

After recording your data, dispose of the solutions in the waste container, and rinse the test tubes. You will then repeat the process for fresh sets of eight known cations and unknowns, continuing to add and mix with the next anion after observing the previous reactions.

After completing the experiment, you'll need to report your findings. Make sure to submit your identified unknown alongside its proper charge and balance the equations associated with it as required. Remember that proper chemical equation writing requires adherence to specific conventions, such as not showing charges in molecular equations and always ensuring that products are formulated based on electro neutrality.

When writing balanced equations, keep in mind that precipitation and neutralization reactions are types of double replacement reactions. Formulating products requires that you adhere to balancing the charges of cations and anions correctly.

As examples are discussed, it is critical to use solubility rules to determine the states of products reliably. You’ll encounter various ionic equations, and understanding how to balance them while being attentive to charge balance will prevent simple mistakes. Finally, the net ionic equation, formed by cancelling spectator ions, needs to indicate any remaining ions that participate in the reaction properly.

When grading, all equation writing will be graded strictly, requiring complete accuracy on every aspect of the chemical equation, including charges and physical states. Therefore, it is essential to pay careful attention to these details and practice on your own to develop your skills for future laboratory work. If you have questions, do not hesitate to ask your instructor.