1. Chem. 1B – 11/12 Lecture

2. Announcements I Mastering Chemistry –Chapter 18 Assignment is due 11/17 Lab –Experiment 9 Report due next week –Quiz on Electrochemistry Today’s Lecture –Electrochemistry (Ch. 18) Electrolytic Cells + Corrosion

3. Announcements II Today’s Lecture – cont. –Transition Elements (Ch. 24) Absorption of visible light Electron configuration and charactestics of transition metals Coordination Compounds (if time)

4. Chapter 18 Electrochemistry Electrolytic Cells Differences with Voltaic Cells –Uses External voltage to drive unfavorable reaction –Charge at electrodes is reversed anode (note: oxidation driven by voltage, but now + charge) cathode (reduction, - charge) Power Supply + -

5. Chapter 18 Electrochemistry Electrolytic Cells Example Reactions 1.Electrolysis of water (opposite of fuel cell example) Anode: H 2 O – oxygen is oxidized to O 2 (g) Cathode: H 2 O – hydrogen is reduced to H 2 (g) 2.Industrial Use – Electroplating (Chrome, nickel, silver plating possible) – using external potential to deposit metal to electrode

6. Chapter 18 Electrochemistry Electrolytic Cells Example Reactions 3.Electrolysis of Mixtures – e.g. analysis External potential will work on easiest to oxidize/reduce pair For example, if we have a mixture of NaI and NaCl in water, electrolysis will cause the following reactions: –Na + (aq) + e - ↔ Na(s) Eº = -2.71 V –H 2 O(l) + 2e - ↔ H 2 (g) + 2OH - (aq) Eº = -0.83 V –2Cl - (aq) ↔ Cl 2 (g) + 2e - Eº = +1.36 V –2I - (aq) ↔ I 2 (aq) + 2e - Eº = +0.54 V –2H 2 O(l) ↔ O 2 (g) + 4H + (aq) + 4e - Eº = 1.23 V

7. Chapter 18 Electrochemistry Electrolytic Cells - Questions 1.Which of the following changes in switching from a voltaic to an electrolytic cell? a)Charge on anode/cathode b)Which electrode (e.g. anode) does oxidation/reduction c)Ion migration to electrode 2.An anode in an electrolytic cell is used to measure oxalate (Eº = -0.49V) in the presence of pyruvate (Eº = -0.70V). Can this be done? What if one is interested in pyruvate?

8. Chapter 18 Electrochemistry Corrosion Most metals are more stable as oxides, so oxidation of metals is common One would think that oxidation is primarily dependent upon Eº values, but oxides like Al 2 O 3 can protect further oxidation of Al metal Iron in particular is prone to rusting Galvanized metal uses a more readily oxidized metal (e.g. Zn) to protect iron

9. Chapter 18 Electrochemistry Corrosion - Questions Using the table below, which metals can be added as a sacrificial agent to prevent iron oxidation? ReactionEº (V) Ag + (aq) + e - ↔ Ag(s)+0.799 Cu 2+ (aq) + 2e - ↔ Cu(s)+0.337 Co 2+ (aq) + 2e - ↔ Co(s)-0.277 Fe 2+ (aq) + 2e - ↔ Fe(s)-0.45 Cr 3+ (aq) + 3e - ↔ Cr(s)-0.73 Mn 2+ (aq) + 2e - ↔ Mn(s)-1.18

10. Chapter 24 Transition Metals Overview –Compared with the main group elements, differences in transition metals are smaller –Variation is in how full d-shell orbitals are –Much of the interesting chemistry is from Coordination Compounds (metal – ligand complexes) –Focus will be on types of compounds and their relationship to the electron configurations

11. Chapter 24 Transition Metals Color –A variety of compounds are colored because they absorb visible light –Most organic compounds have strong bonds and a large energy gap between ground and excited states –Transition metals, in coordination complexes, tend to have weaker bonds and smaller energy gaps, so that they often absorb visible light

12. Chapter 24 Transition Metals Color – Cobalt Chloride Compounds –In Quantitative Analysis Lab, we analyze an aqueous mixture of Co 2+ and Cr 3+ –Students tend to think that Co 2+ is the blue solution (it is the red/purple solution) –Why? Co in inorganic compounds (anhydrous CoCl 2, CoO) is blue, but in a coordination complex with water it turns red/purple –This is the basis for indicator Drierite (show samples)

13. Chapter 24 Transition Metals Properties –D-Block Elements (show on periodic table) –Electron Configuration nS and (n-1)d shells are similar in energy (depends on several factors) transition metals start on the 4 th row because only 3 rd row (n = 3) capable of having d shell Filling goes 4s → 3d → 4p (with a few exceptions) or 5s → 4d → 5p (for 5 th row) Filling for 6 th row is more complicated: 6s → 4f (lanthanides) → 5d → 6p

14. Chapter 24 Transition Metals Properties – cont. –Filling exceptions – 1 st row Cr (4s 1 3d 5 instead of 4s 2 3d 4 ) and Cu (4s 1 3d 10 instead of 4s 2 3d 9 ) due to extra stability of half- and completely-filled d orbitals –Electron Configuration – for ions electron removal in oxidation is different: first lost are ns electrons and then (n-1)d electrons reason is because outside a cation, (n-1) d electrons are more strongly attracted to the nucleus than the ns electrons

15. Chapter 24 Transition Metals Properties – cont. –Size decreases slightly across a row so right hand transition metals (e.g. silver) are more dense than left hand metals (titanium) –Oxidation State All elements but Cu column will lose 2 ns electrons (Cu column is stabilized in +1 state due to full d orbital) Left hand side elements tend to lose additional d orbitals (up to complete emptying)

16. Chapter 24 Transition Metals Questions 1.Give the electron configurations for: V, Fe, Ni, Cu, Fe 3+ and Ni 2+ 2.Explain why Fe 3+ is a stable ion while Mn 3+ is not very stable. 3.Why are only the elements Cu and Ag able to form stable +1 oxidation states? 4.What is the maximum oxidation state expected for V?

17. Chapter 24 Transition Metals Coordination Complex –Covered previously (to some degree as complex ions) in Chapter 16 –Coordination complexes consist of: metal ion (typically same charge as will exist in water although stability of different oxidation states – such as Fe 2+ vs. Fe 3+ can change) ligand(s) counter ions (not part of complex, but associated with complex ion)

18. Chapter 24 Transition Metals Coordination Complex – cont. –Both the metal (covered more later in the chapter) and ligand affect the type of coordination complex formed –Types of ligands: monodentate (one metal – ligand bond per ligand) bidentate (two metal – ligand bonds per ligand – so requires to parts of ligand capable of acting as Lewis bases)

19. Chapter 24 Transition Metals Coordination Complex – cont. –Examples: Ag(NH 3 ) 2 + = [Ag(NH 3 ) 2 ] + –Ni(C 2 O 4 ) 2- H 3 N-Ag-NH 3 linear structure – uncharged monodentate ligand oxalate is a bidentate ligand and forms a “square planar” complex (view from above)