Introduction

Lewis acids and Lewis bases can be used in a variety of ways in Chemistry, especially when they’re combined with ligands. After a Lewis Acid-Base reaction occurs involving a ligand, either complex ions or coordination compounds form. When a neutral metal atom becomes surrounded by and bonded to other neutral atoms, it is known as a coordination compound, and typically ends up as a solid precipitate after a reaction. A complex ion is a coordination compound that is either positively or negatively charged, and typically shows up as a brightly colored, aqueous, clear solution after a reaction. This makes distinguishing these two types of compounds very easy in the lab.

Not only can coordination compounds and complex ions be distinguished from each other, but each coordination compound and complex ion has its own unique properties, such as different colors, textures, and melting points. Solutions containing known cations can be mixed with different Lewis acids and bases to make a product of a specific color and texture. The findings from that experiment can then be used to identify the cations of an unknown solution.

Procedure

Eight bottles of aqueous, 0.2 M solutions of eight different cations were obtained, along with a variety of acids and bases. A few drops of each cation solution were put inside of their own test tube. Then, exactly five drops of an aqueous 3.0 M Sodium Chloride (NaCl) solution were added to each test tube, and observations were recorded. After that, eight new test tubes were obtained, and each were filled with a few drops of one of the cations. Five drops of 6 M Hydrochloric Acid (HCl) were added to each test tube, and once again, observations were recorded. In both instances, the samples that contained solutions of Silver Nitrate and Lead (ii) Nitrate were kept and exposed to heat, and observations were recorded.

Similar experiments using the cation solutions and various other Lewis acids and bases were done. Sometimes, after a reaction was performed, a solution was exposed to heat to determine whether or not a precipitate would melt. Other times, the solution was washed with DI water and centrifuged to obtain a purer solid after a reaction resulted in a cloudy solution.

Finally, confirmatory tests specific to each cation were performed, producing results that were entirely unique to each of the eight cations. These numerous experiments were done so that known cations mixed with known Lewis acids and bases could be catalogued and later used to identify a solution containing four unknown cations.