Purpose: At the moment, our class is studying the periodic table, and how different elements on the table interact with each other, especially members of the same group or period. The lab we will do will help us identify and understand how these elements are similar or different from each other. We will be using eight different chemicals, one of which is unknown, and combine them with each other, testing the solubility of each pair. We will be combining members of the alkaline earth metal group with two non-metals (Carbon and Sulfur), and a transition metal (Chromium). I hypothesize that the alkaline earth metals will not be soluble in the non-metals, but will be soluble in the chromium, because they are metals themselves.
Data and Calculations:
| | H2So4 | CO32- | CrO42- |
| Mg2+ | S | I | S |
| Ca2+ | S | I | S |
| Sr2+ | I | I | I |
| Ba2+ | I | I | I |
| Unknown | S | I | S |
| Unknown #12 or 20 Identity of cation of unknown: Magnesium, or Calcium. | |||
S = Soluble
I = Insoluble
Analysis:
1) There is a relationship that occurs between the solubility of salts containing alkaline earth metal ions and the position of the metals in the periodic table. First, if mixed with sulfuric acid, the lower down the group you go, the less soluble the substance is. It is the same with the chromium peroxide. However, the carbon substance does not mix with any alkaline earth metal in question.
2) The unknown substance reacted similarly to the magnesium and calcium ions. However, since the results of all three of these substances were exactly the same, it is impossible to determine which element, if any at all, the unknown is. However, it is definitely not strontium or barium, because, unlike those two, it dissolved in sulfuric acid, and in the chromium peroxide solution.
Results/Discussion: From this lab, I have discovered that the top half of the alkaline earth metals are soluble in sulfuric acid, and chromium peroxide, unlike the bottom half, which is insoluble. None of the elements from this group were soluble in the carbon solution, however, which rendered the entire column of the observations useless in trying to identify the unknown. The unknown ended up with being either a magnesium, or calcium ion. I am not sure if this data is correct, for I could not find any resources that suggest the solubility of these four metal ions with the three chemicals that we tested them on. However, it seems logical that I could not determine the unknown, because the analysis question suggested a problem of this sort. Some errors that my partner and I could have made include the failure to make more detailed observations, and the contamination of one chemical into another test tube, where it was not supposed to be. The purpose of this lab was not accomplished. From the limited information, and the blind way we did the laboratory, I did not quite understand the similarities and differences. Yes, the elements in the second group all failed to mix with the carbon substance. Yes, they had opposite results for the other two substances. That shows three unique cases. However, there are thousands more compounds that can be poured into the same flask as these metals. This lab gave me no idea of how they might react then. My hypothesis was also incorrect. I predicted that the metal ions would dissolve in the chromium, but not the non-metals. It turned out, that none dissolved in the chromium, and only half dissolved in the non-metals. This lab did not help me understand our topic. Instead, it only served to confuse me more. I know that the lab relates to our topic, because we are studying how groups of elements are similar, but that is as far as I can see. The lab proves that in most cases, the elements of a group are not similar, since 66% of the time the behaviour of the alkaline earth metals did not match. Without additional explanation, I do not understand the reason for this lab.d
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