2Outline Purpose Coordination Complexes Reaction Determining “n” Graph of Abs vs. Mole Fraction of SCN-ProcedureSafety ConcernsWasteSubmit Lab 11 Reports on…
3PurposeStudents will become familiar with Job’s method of Continuous variation, which is a technique for determining the empirical formula of a coordination complex.
4Coordination Complexes A coordination complex consists of a central metal ion bound by surrounding ligands.Transition metals are positively charged and will readily accept electrons.Ligand molecules contain atoms with non-bonding electrons, which can be donated to the electron deficient metal ion in order to form a complex ion.This can be viewed as Lewis acid – base chemistry because of the electron involvement.
5ReactionFe3+ + nSCN- [Fe(SCN)n]3-n iron (III) thiocyanate iron (III) thiocyanate metal ion ligand complex ion We will experimentally determine the value of “n.”
6Related to the value of “n”: The coordination number of a metal ion is the number of bonds it can form with ligands – typically 1, 2, 3, 4, 5, or 6. The coordination number of Fe3+ is 6.Iron (III) can therefore bond to as many as 6 monodentate ligands or three bidentate ligands.
7XLigand vs. XSCN- For the purpose of this lab: Xligand refers to the mole fraction of SCN- in each solution (of SCN- + Fe3+).XSCN- refers to the mole fraction of SCN- in the compound [Fe(SCN)n]+3-n.
8To determine “n”:We will prepare a series of solutions, each with a different mole fraction of ligand:The absorbance of the complex at = 470 nm is directly proportional to the concentration of the complex.
10GraphThe point of intersection of the two linear extrapolations corresponds to the mole fraction of SCN- in the complex ion.Remember to limit your graph slopes to the appropriate significant figures and y-intercepts to the appropriate digits of precision before attempting any calculations.Solving for the intersection we are solving for x where:y1 = y2m1x + b1 = m2x + b2b1 – b2 = m2x – m1x = x (m2 – m1)
12ProcedurePrepare your solutions following the directions in the manual.Measure the absorbance of each solution at a wavelength of 470 nm.Apply Job’s Method to your data to determine the empirical formula of your complex.
13Safety Concerns Reagents: Eye Contact: Skin Contact: Inhalation: Ferric Nitrate (Fe(NO3)3HNO3 (1.0N)Potassium Thiocyanate (0.1N)Sulfamic AcidEye Contact:Blurry vision. Severe irritation, redness, pain, burns, conjunctivitis and permanent corneal damage.Skin Contact:Severe irritation, burns, redness, pain, stains and ulcers.Inhalation:Destructive to mucosa and upper respiratory tract. May cause burning, coughing, choking, wheezing, laryngitis, shortness of breath, headache, nausea, vomiting, methemoglobinemia, cyanosis, convulsions, tachycardia, dyspnea, pneumonia, pulmonary edema, asphyxia, chemical pneumonitis and death.Ingestion:Pain and burns of the mouth, throat, esophagus and gastrointestinal tract. Gastrointestinal irritation with nausea, vomiting, diarrhea, methemoglobinemia, cyanosis, convulsions, systemic toxic effects on the heart, liver, and kidneys and death.
14Waste Conserve chemicals and distilled water. If you spill, clean it up.All solutions in this experiment are acidic. Dispose of all excess and waste solutions in provided acid waste containers in the fume hood(s).Please DO NOT unplug the hotplates!
15Submit Lab 11 Reports:Your instructor will let you know when to submit your Lab 11 reports for preliminary grading.