You have been given a well plate, several test tubes and pipets, a concentrated ammonia solution, ac — Coordination Chemistry Chemistry Question
Problem Context
You have been given a well plate, several test tubes and pipets, a concentrated ammonia solution, access to distilled water, and four numbered vials containing iron (III) chloride hexahydrate, cobalt (II) sulfate heptahydrate, copper (II) chloride dihydrate, and potassium oxalate monohydrate, though not necessarily in this order. Devise and carry out an experiment to produce at least FIVE new different complex compounds, using your understanding of coordination compound geometry and qualitative evidence in your results.
Give a brief description of your experimental plan.
Model Answer
Students were expected to create different complex compounds by combinations of the hydrate compounds provided with the aqueous ammonia solution. Students might have thought also to react the hydrates with an aqueous oxalate solution or to slowly add water to samples of each hydrate. For example, adding H2O slowly to a small amount of copper(II) chloride in one of the test tubes produces a color change as the dihydrate of this salt forms a tetrahydrate.
Data and Observations.
Vials Contents as correctly written formulas Evidence
#1
#2
#3
#4
Model Answer
Vial 1: Yellow-Orange, FeCl3 . 6H2O
Vial 2: Pinkish, CoSO4 . 7H2O
Vial 3: Green, CuCl2 . 2H2O
Vial 4: White, K2C2O4 . H2O
Show any relevant reactions and sketch the possible geometry of each formed compounds.
Model Answer
Compound Possible Formula Observation
CuCl2 . 2H2O + H2O → CuCl2 . 4H2O (green to blue)
CuCl2 . 2H2O + ammonia solution → Cu(NH3)4 (deep blue color change)
CoSO4 . 7H2O + ammonia solution → Co(NH3)6 (bright blue-green color change)
FeCl3 . 6H2O + ammonia solution → Fe(NH3)6 (Brown-purple gelatinous ppt.)
K2C2O4(aq) + FeCl3 . 6H2O → K3[Fe(C2O4)3] (greenish color change)
K2C2O4(aq) + CuCl2 . 2H2O → K2[Cu(C2O4)2] (greenish color change?)
Ammonia replaces water in these hydrated compounds to produce complexes that include NH3 surrounding the central metal cation. Possible formulas might also include ligand combinations of ammonia, water, and chloride or sulfate as part of the complex. Possible sketches of these structures show the central Cu, Fe, and Co cations surrounded by the NH3 ligands in tetrahedral, square planar geometry, or octahedral geometries.
Conclusions
Reactant(s) Used Proposed coordinate complex formula Evidence
Model Answer
Excellent Results: Students attempted as many matches as possible, creating a legible and systematically organized table to communicate their results. The nomenclature of the possible complexes was clear and the formulas used the proper coordinate complex compound was accurate. Drawings for the possible structures included three-dimensional representations of the complexes and indicated how and where isomers might also be formed. It was drawn/noted that the oxalate ion was a bidentate and three ions were able to coordinate with the iron (III) cation.