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The purpose of the Coordination Compound Synthesis (CCS) Lab was to synthesize and analyze a coordination compound of iron with an unknown chemical formula, KaFeb(ox)c × dH2O. This was achieved by combining 8.3 grams of potassium oxalate [ K2C2O4 (s)] with 10.0 mL of iron (III) chloride (FeCl3) solution to synthesize a green crystalline product. The crude product derived from the combination of the solutions was then purified. The pure product was achieved through a series of recrystallization processes of the crude product.
Once the product was purified and isolated, a series of titrations were performed to determine the percent composition of each element in the compound. The chemical formula of the product was then calculated. The percent yield of each element in the compound was approximately: 20% K+, 11% Fe, 57% oxalate, and 12% H2O. The experimental chemical formula determined from the percent yield is as follows: K2.6[Fe1(ox)3.3] × 3.4 H2O.
A coordination compound, or a complex ion, is composed of a central metal ion that is combined with ligands or dentates (2).
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The ligands, or dentates, are essential to the compound because they are neutral molecules containing lone pairs of electrons (2). These ligands donate their pairs of electrons in order to form a coordinate covalent bond with the metal ion present (2). In the CCS experiment, the oxalate (C2O4), is a bidentate ligand.
The CCS lab uses many important techniques, however, titration is the key component to finding the percent composition of each component of the compound. Titration is an experimental process that determines the concentration and proportions of a given solution.
It has a diverse use of applications and is used in many different industries. For example, it is used in the pharmaceutical industry to test various medications in means for quality control (1). In this experiment, the titration is used to determine the percent composition of the unknown compound. Although the oxalate can be determined through direct titration, the percent composition of K+ ion and Fe3+ can only be determined after the solution has undergone the process of ion exchange.
Ion exchange is made possible when a solution is processed through an ion exchange column. In the CCS experiment, a cation exchange column is used (3). This is a device that contains solid resins that are water insoluble. These resins replace the K+ ions with an equal amount of H+ ions , which results in a solution of H+ and iron-oxalate anion when the solution is passed through the device (3). This device allows for the solution to be titrated, which then allows for the composition of the solid to be determined.
The percent composition of the compound is determined when the solution that has undergone ion exchange is titrated with a strong base (NaOH). The first equivalence point in the ion-exchanged solution signifies the neutralization of the H+ ions. The second equivalence point represents the formation of Fe(OH)3 from the reaction of Fe3+(3).
The Coordination Compound Synthesis (CCS) Lab was composed of a three part procedure. The first step of this lab was to form the crude product. Using a Dial-a-gram balance, 8.3 grams of potassium oxalate (K2C2O4 × H2O) was weighed out and placed into a 125 mL Erlenmeyer flask. Then, 4.1 grams of iron (III) chloride (FeCl3 × 6H2O) was weighed, and placed into a 150 mL glass beaker. 10.0 mL of deionized water was then added to the solid iron (III) chloride, and stirred until dissolved. Once the iron (III) chloride solution was prepared, the solid K2C2O4 × H2O was added. The beaker containing the iron (III) chloride and potassium oxalate solution was then set aside and covered with a cardboard square. Once the precipitate formed, the beaker was placed in an ice bath for 30 minutes in order to speed up the crystallization process.
After the precipitate formed, the crystalline precipitate was recrystallized to remove any impurities. To do this, a Büchner funnel was set up and the solution was poured through it, in order to isolate the solid precipitate from the liquid solution. The isolated precipitate was then dried and placed into a clean, dry beaker. 10-15 mL of deionized water was added to the solid crystalline product in the beaker. The beaker was then placed on a heating plate, heated to 80℃, and stirred until the precipitate was completely dissolved. Once dissolved, the beaker was removed from the heating plate and covered with a watch glass until the product recrystallized.
The third step of the CCS Lab was to determine the chemical formula of the crystalline compound. First, the purified precipitate was isolated from the solution using a Büchner funnel once again, and weighed out into two 0.125 gram samples. These crystalline product samples were then placed into two Erlenmeyer flasks. 60 mL of deionized water, 6 mL of 6M H2SO4, and 1 mL of 85% concentrated H3PO4 was then added to each flask. One sample was placed on a heating plate until the solution reached around 80℃. Then, a burette was filled with KMnO4 and attached to the ring stand for the first titration. Once the crystalline solution reached 80℃, a stir bar was placed into the flask and the solution was titrated with KMnO4. The equivalence point of the titration using KMnO4 was then determined by observation of the pH curve produced by the Vernier Logger Pro application.
This process was repeated for the second sample. Next, 0.16 grams of the crystalline product was measured and added to a separate glass beaker. 4 mL of deionized water was added to the crystalline product. The ion exchange column was then set up, and the solution containing the crystalline product was poured through the resin and collected in a beaker below the column. Then, using a pH probe, two equivalence points of the solution following the ion exchange were determined while titrating the solution with NaOH. Lastly, the waste was disposed of in the designated containers and equipment was cleaned and put away.
It was hypothesized that the chemical formula of the experimental would be comparable to that of the literature value. Throughout both trials during the titration of the crystalline product with KMnO4, the solution held a light pink color after roughly 31 mL of KMnO4 was used. After the solution was filtered through the ion exchange column, it took 22.2 mL of NaOH to titrate the solution. As seen in figure 3 below, there are two titration curves apparent. The first curve represents the first equivalence point (at 8.37 mL), which signifies the neutralization of the H+ ions. The second curve signifies the second equivalence point (at 17.74 mL) which represents the formation of Fe(OH)3 from the reaction of Fe3+. These data points were then used to calculate the percent by mass of each element in the compound. From there, the coefficients were determined by dividing the moles of each element by 0.196. The formula for this compound was K2.6[Fe1(ox)3.3] × 3.4 H2O. Overall, the experimental value had a 3.67% error.
One possible source of error that likely occurred could have been from not obtaining all of the crystalline product from the beaker before proceeding with the experiment. It was also noted during the first part of the experiment that no precipitate had formed within the 30 minute time period. This could be due to faulty measurements on the Dial-a-gram balance. Finally, a third source of error could be due to the ion exchange resin not being fully saturated before passing the solution through. This could have impacted the data because the solution may have not been filtered very efficiently, resulting in an impure solution. The impurities could have skewed the results of the titration, thus impacting the chemical formula of the compound.
Calculation for Relative Amounts/ Chemical Formula:
Example: K+ percent by mass = 20% (assume)→ 20g K+
Example: Percent by Mass H2O
Percent by mass C2O4 2− + Percent by mass K+ + Percent by mass Fe3+ = 88%
100% - 88% = 12% by mass H2O
Example: Calculation for Chemical Formula Coefficients
12g H2O = 0.667 mol
0.667 mol H2O 0.196 = 3.4H2O
Percent Yield:
g K3[Fe(ox)3]2
Example for Calculating Moles (Oxalate, C2O4):
Moles of C2O4=Molar Mass of C2O4Grams of C2O4
Percent Composition Calculation:
Percent Composition=(Total Mass of CompoundMass of Element in Compound)×100
Chemical Formula Determination:
Given the percent composition, the relative molar amounts of each element were calculated, leading to the formula: K2.6[Fe1(ox)3.3] × 3.4 H2O.
The goal of the Coordination Compound Synthesis Lab was to synthesize the coordination compound of iron and analyze to determine the unknown coefficients of the chemical formula; KaFeb(ox)c × dH2O. Through the process of titration, the percent by mass of each element in the compound was determined. The percent by mass for each element in the compound is as follows: 20% K+, 11% Fe, 57% oxalate, and 12% H2O. This data was then used to calculate the coefficients for the chemical formula. The experimental chemical formula was K2.6[Fe1(ox)3.3] × 3.4 H2O.
Synthesizing and Deciphering the Chemical Formula of an Iron Coordination Compound. (2024, Feb 23). Retrieved from https://studymoose.com/document/synthesizing-and-deciphering-the-chemical-formula-of-an-iron-coordination-compound
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