March 20, 2015
The purpose of this lab is to identify unknown ions in a solution by using a type of chemical reaction called precipitate reactions. The key to finding which ions are present in a solution is to form a precipitate which makes the ions “come out” in a reaction (McNeil, 2013-2014). Water is used in these experiments to act as a solvent. Since water is a polar molecule, the slightly positive and negative charges will sometimes pull apart molecules and surround them based on charges. In other words, water can dissolve ionic compounds and create an aqueous (aq) solution. This lab uses no quantitative analysis, but is entirely based on qualitative analysis which is the observed result instead of the measured result. Looking for a precipitate is qualitative in that physical changes are what is being observed and noted. Precipitates generally have a solid, cloudy or milky substance that does not dissolve easily and occurs when a cation and anion combine in an aqueous solution, but reacts to become insoluble (Precipitation Reactions). This lab uses two methods in testing for precipitates: spot testing and a flowchart. Spot testing requires two ionic compounds that are dissolved into a solution to be added together. When the ions separate and reform new bonds to form a precipitate, the physical changes are recorded. Some substances are not soluble, thus will not dissolve in water which is called insoluble. The solubility rules are located on page 67 to 68 in lab manual and explain when a precipitate will occur. Unknown mixtures of compounds are hard to separate and individually identify, thus the flowchart is used. A flowchart is an outline that separates cations from anions where they can then be tested through spot testing. A real world example of qualitative analysis could be used in athletics. Many coaches will say, “Quality over quantity,” when referring to drills. Coaches are looking for...
Cited: McNeil, H. (2013-2014). Chemistry 141 Labratory Manual. Department of Chemistry and Biochemistry, Montana State University-Bozeman.
Precipitation Reactions. (n.d.). Retrieved from Chem Wiki: http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Reactions_in_Aqueous_Solutions/Precipitation_Reactions
Wicks, K. M. (2014). Double Displacement Reactions. Retrieved from Chemistry Lecture Notes: http://www.chemistrylecturenotes.com/html/double_displacement_reactions.html
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