Question

2. It is the oxalate ion (C2O4 2- ), which is the conjugate base of oxalic acid, that will serve as the chelating agent for Fe3+ in our experiment. The goal is to determine the empirical formula of the coordination compound that will form. Let’s imagine some of the possibilities.

a. A complex ion is comprised of a metal atom or ion at its center, to which is bonded molecules or ions (called ligands). What are the common coordination numbers of complex ions? Depict via one or more sketches (labeling the metal M and ligands L)

b. Give the formula of the compound comprising a complex ion with two oxalate ions bound to a single Fe3+ ion, potassium counterions, and two waters of hydration. _____________________________________.

c. Give the formula of the compound comprising a complex ion with three oxalate ions bound to a single Fe3+ ion, potassium counterions, and four waters of hydration. _____________________________________.

4. When performing the first synthetic step (See procedure #3 in the online lab manual), we are instructed to digest our precipitate by placing the reaction beaker in a boiling water bath containing boiling chips. In one sentence, what is the purpose of the boiling chips? (Hint: Consult Wikipedia).

5. Since most reactions do not go to completion or afford byproducts, the crude product is more or less contaminated with other compounds. If it is a solid, recrystallization is a common way to purify the crude product.

a. Solvent selection is an important first step in any re-crystallization; the correct solvent is required to form a product of high purity and in good recovery or yield. Why is 95% ethanol a good solvent choice for the (re)-crystallization of our final product, Kw[Fex(C2O4)y]× zH2O(s)?

b. Following solvent selection, the re-crystallization technique involves 4 more steps: (1) Dissolving the compound in a minimum amount of (heated) solvent; (2) Removing insoluble and/or colored impurities; (3) Crystallization; and (4) Collecting, washing, and drying the crystals. Why do we want to be careful not to add too much solvent in Step 1?