This experiment tested the theory that the elements in the periodic table are arranged in a manner in which the elements of a group share similar chemical properties. The elements we used were the ones from the alkaline earth metal group. These elements tend to form 2+ cations and are very reactive. We also compared these elements to that of lead because lead also forms a 2+ cation. We used the chemical property of solubility to observe the periodic trends of the alkaline earth metals.
As a general rule, reactivity increases as you move down a group in the periodic table. This means in regards to solubility that the more you farther you move down the group the more insoluble the element is when combined with hydroxides, chlorides, bromides, iodides, sulfates, carbonates, and oxalates. My results were consistent with this theory in that the mixtures went from no reaction to forming a precipitate or from forming a light precipitate to a heavy one as the elements moved down the periodic table.
The precipitates that were formed gradually changed from a cloudy or milky mixture to a heavy solid precipitate that would settle on the bottom of the test tube. In some instances lead reacted very similarly with the alkaline earth metal but very different in the other reactions such as with iodide. This is due to lead’s position on the periodic table as compared to those of the alkaline earth metals. The position on the periodic table correlates to an element’s atomic radius, ionization energy, and electron affinity. All of these properties affect an element’s chemical properties such as solubility.
A systematic error occurred during my experiment when I observed a reaction between barium and iodide. There should have been no reaction. This error is probably the result of using a test tube that was not cleaned properly prior to combining Ba(NO3)2 with NaI. This experiment reinforced the concepts introduced in Chapter 8 of our textbook.
1.The names and symbols of the alkaline earth metals encountered in this experiment are:
a.Magnesium – Mg
b.Barium – Ba
c.Strontium – Sr
d.Calcium – Ca
2. a. The general electron configuration of the alkaline earth metals is [Noble gas]ns2.
b. The electron configuration for lead, Pb, is [Xe]6s25d104f146p2.
c. All the formulas of the oxides formed by the alkaline earth metals and lead have the general formula of RO.
3. The general formulas for the following compounds with alkaline earth metals or lead:
4.The general method that was used to examine qualitative solubilities in this experiment is observation.
Post Lab Questions
- The solubility of the alkaline earth metals with hydroxides increases as you move down the group; soluble with halides; with sulfates, carbonates and oxalates decreases as you move down the group down the group.
- The solubilities between alkaline earth metals and lead with NaOH are similar because all of the reactions were either cloudy or milky. The solubilities between alkaline earth metals and lead with NaCl are different because all of the alkaline earth metals are soluble but lead is not. The solubilities between alkaline earth metals and lead with NaBr are different because all of the alkaline earth metals are soluble but lead is not.
The solubilities between alkaline earth metals and lead with iodide are different because all of the alkaline earth metals are soluble but lead is not soluble and formed a bright yellow precipitate. The solubilities of Mg and Ca with SO4 are different because they are soluble but lead is not and solubilities of Sr and Ba are similar to lead.
The solubilities between alkaline earth metals and lead with CO3 are similar since all of compounds form some sort of a white precipitate. The solubility of Mg with C2O4 is different from lead because it is soluble but lead is not and solubilities of rest of alkaline earth metals are similar because they all form some sort of white precipitate.
3.The solubilities of the alkaline earth metals and that of lead may differ markedly due to their respective electron configurations. The alkaline earth metals like to give up two electrons from their outer shell and form cations because by doing so their electron configuration becomes isoelectronic with the closest noble gas. Lead looses its to electrons from the 6p suborbital.
- Chang, R. (2010). Chemistry: 10th Edition. New York, NY: McGraw Hill.