THE CHEMISTRY OF FIVE ANIONS. - Pomona College

THE CHEMISTRY OF FIVE ANIONS. - Pomona College

THE CHEMISTRY OF FIVE ANIONS Purpose? 1) Explore different types of reactions via observations. 2) Devise experimental method to identify two unknown anions in a mixture. FIRST WEEK LAB Test of reactivity via observations of all possible combinations. FIRST WEEK HOMEWORK In groups of 3-4 devise experimental method to identify a solution with 2 unknowns Work on net ionic equations for reactions observed (pre-lab). SECOND WEEK LAB Turn in experimental method (each student) - can be typed or yellow sheet - have a copy for yourself to follow Group discussion of methods Make revisions Carry out revised methods to identify ions Group discussion of net ionic reactions 1

1) Classes of Reactions Precipitation Acid/Base Oxidation/Reduction (redox) Complexation Anions & carbonate oxalate nitrite bromide hydrogen sulfate Reagents acid/base, possible redox nitric acid cobalt (II) nitrate complexation, ppt. ppt. barium nitrate sodium hydroxide acid/base hydrogen peroxide/H+ redox (bisulfate) 2

Today: Observations of Reactivity Anions are in 1- mL dispensers. Reagents are in bottles. (Do not waste.) Add the reagent drop-wise Observe after first few drops Observe after excess (mixed well) If no reaction observed 2nd test measure T 2 mL REAGENT, 1 mL ANION, measure T before and after Demonstration Common errors: contaminated equipment faulty recording of observations not recording both drops & excess results illegible notebook 3 Next Week Method Development in Groups before next class: Develop procedure to identify two anions in mixture Flow Chart often works well Reagent added Possible Observation Interpretation, Conclusion, Next step Usually 3-4 tests required to unambiguously identify anions Be careful of possible interference from other anion Record method in notebook (list group members) Turn in yellow sheet/copy at beginning of 2nd week along with pre-lab Presentation of method/critique by class

Individually carry out revised experimental method Group works on Net Ionic Equations Lab due beginning of lab period of following lab experiment 4 M O N O D E N T A T E L I G A N D S 5 Types of ligands BIDENTATE LIGANDS. Form two bonds to the central atom.

6 EXTRA INFORMATION FOR 5 ANIONS EXPERIMENT Precipitation Definition/ Experimental Observables formation of solids Acid/Base pH change temperature change rxn of known acid/base pairs Redox Complexation complexes often colored reaction of a transition

metal with a ligand involves transfer of electrons involves changes in oxidation states reactions with O2, H2, or other known oxidizers or reducers lists of common strong oxidants and reductants on website, standard reduction potentials in Appendix E in Oxtoby -- meaning of standard reduction potentials to be discussed later discussion pp. 131-132, Oxtoby, examples of ligands given in Table 19-1, p. 811 and bidentate ligands in Fig. 19-2, p. 812 in Oxtoby

Additional Information (solubility rules on page 147-149 in Oxtoby, values of solubility product constants in Table 9-1, p. 405 in Oxtoby) meaning of solubility product constants to be discussed later) lists of common acids/bases and their pK's in Table 8-2, p.355 in Oxtoby) meaning of pKa's to be discussed later 7

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