Qualitative Analysis: Identifying Unknown Ions In A Solution

Carlie Haeffner
Qualitative Analysis
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
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 concentration and complete effort in doing a drill correctly a few times rather than doing a drill many times without full effort and
In order to make an ion “come out,” using what we know about the solubility rules we are able to take advantage of the compounds and separate them as well as see how new ones are chemically bonded together. The ions are separated by being dissolved in a solution, usually water. These water molecules completely surround the ion which allows them to flow freely in the solution. Some compounds have a stronger bond then the substance that the compound is being put in and will not dissolve remaining to be soluble. When mixing two different ionic compounds together that have been dissolved in a solution, there is a greater chance of a reaction to occur because the compounds are already broken apart (McNeil, 2013-2014). An anion particle will then easily react with a cation particle which causes a precipitate, but some anions and cations in a solution may not react and remain dissolved in the solution. An example of this would be silver has a 1+ charge while a chlorine ion has a 1- charge. These two elements are then attracted together because of opposite charge and form a precipitate because it is not soluble according to the solubility rule #4. A type of reaction where two different compounds are dissolved in the same solution and the cations in each compound switch places is called a double displacement reaction (Wicks, 2014). This further explains why ions form