1 / 16

A very, very, very bad joke…

A very, very, very bad joke…. A cation and an anion were walking down the street…. …and the cation says to the anion , “Whoa, I think I lost an electron!”. The anion replies, “Are you sure?”. …to which the cation replies, “Yes…I’m POSITIVE !”. < FORCED LAUGHTER >.

sasha-whitaker
Download Presentation

A very, very, very bad joke…

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A very, very, very bad joke… A cation and an anion were walking down the street… …and the cation says to the anion, “Whoa, I think I lost an electron!” The anion replies, “Are you sure?” …to which the cation replies, “Yes…I’m POSITIVE!” <FORCED LAUGHTER> www.bitterfilms.com

  2. Al0 has been oxidized:Its oxidation state has increased from 0 3. Al3+ has been reduced:Its oxidation state has been reduced from 3 0. Cations and Anions and Electrons, Oh My! Al0 Al3+ + 3e- 13 ____ protons ____ protons ____ electrons ____ electrons 13 13 10 Al0 has lost 3 electrons. Al3+ Al0 + 3e- 13 ____ protons ____ protons ____ electrons ____ electrons 13 10 13 Al3+ has gained 3 electrons.

  3. NaBr (aq) + AgNO3 (aq) NaNO3 (aq) + AgBr (s) HBr (aq) + LiOH (aq) LiBr (aq) + H2O (l) Al0 Al3++ 3e- I20 + 2e- 2I- Redox Reactions: A New Type of Reaction All chemical reactions can be categorized, roughly into: • Acid-base reactions – depending on your definition • Displacement reactions – exchange of ions • Acid-base reactions – exchange of H+ or OH- • Oxidation-Reduction (redox) reactions – exchange of electrons

  4. Redox Rules! Calculating Oxidation States O 1. Oxidation states for elements are always zero. e.g. N2(g), Co(s), H2(g), C(gr), P4(s), Na(s), Ne(g) H H 2. Oxidation states for monatomic ions are the same as their charges. e.g. Al3+, Cd2+, Zn2+, Ag+,and Group IA(1) and IIA(2) ions 3. The oxidation state of oxygen is usually 2-, except for peroxides (-1). e.g. Na2O, Al2O3; compare with H2O2, Na2O2 – remember, O22- 4. The oxidation state of hydrogen is usually 1+, except for hydrides (-1). e.g. H2O, OH-; compare with NaH, LiAlH4 – look for H bonded to metal 5. The oxidation state of halides are 1-, except when bonded to oxygen. e.g. HF, NaCl, MgBr2 (F is always 1-); compare with ClO3- 6. The oxidation numbers MUST add up to the molecule’s total charge.

  5. Cr2O72- TiCl4 H2SO3 BaO2 P2O5 More Practice with Oxidation States Cr = ? O = -2 Cr = +6 dichromate 2(?) + 7(-2) = -2 4 Cl = 4(-1) titanium(IV) chloride +4 Ti = +4 S = sulfurous acid 2(-1) 2 O = barium peroxide 2(+5) 2 P = diphosphorus pentoxide

  6. Al: 0 +3 I: 0 -1 Back Again?! Aluminum and Iodine Al (s) + I2 (s) AlI3 (s) 3(-1) 2(0) +3 0 So, now that you know oxidation states…what is oxidized, and what is reduced?

  7. GER LEO Mnemonic Devices for Remembering Redox Rules LEO the lion goesGER When an atom/molecule Loses Electrons, it is Oxidized. -its oxidation state becomes more positive -it is the reducing agent, or reductant When an atom/molecule Gains Electrons, it is Reduced. -its oxidation state becomes more negative -it is the oxidizing agent, or oxidant Oxidation Is Loss O I L Reduction Is Gain R I G http://www.franklinhoward.com/

  8. Al: 0 +3 I: 0 -1 Back For Good!! Aluminum and Iodine Al (s) + I2 (s) AlI3 (s) 3(-1) 2(0) +3 0 decreases oxidation state increases oxidation state gains electrons loses electrons reduced I2 is oxidized Al is oxidizing agent I2 is the reducing agent Al is the 2 Al (s) 2 AlI3 (s) 3 I2 (s) +

  9. Identifying Oxidizing/Reducing Agents Oxidizing/reducing agents are ALWAYS REACTANTS! Oxidizing agents (oxidants) are reactants that are REDUCED. Reducing agents (reductants) are reactants that are OXIDIZED! Zn (s) + 2H+ (aq) H2 (g) + Zn2+ (aq) 2(+1) 2(0) +2 0 Zn loses/gains electrons H+ loses/gains electrons Zn is oxidized/reduced H+ is oxidized/reduced Zn is the reductant/oxidant H+ is the reductant/oxidant

  10. Identifying Oxidizing/Reducing Agents Oxidizing/reducing agents are ALWAYS REACTANTS! Oxidizing agents (oxidants) are reactants that are REDUCED. Reducing agents (reductants) are reactants that are OXIDIZED! 2 H2O (l) + Al (s) + MnO4- (aq) Al(OH)4- (aq) + MnO2 (s) +4 0 +3 +7 What is oxidized? What is reduced? Al (s) MnO4- (aq) What is the oxidizing agent? What is the reducing agent? MnO4- (aq) Al (s) How many electrons are transferred? 3 e-

  11. AgNO3 (s) Ag+ (aq) + NO3- (aq) H2O Ag+ (aq) + e- Ag (s) Cu+ (aq) + e- Cu (s) Practical Applications: Electroplating Electroplating deposits coats of metal onto objects Bronze baby shoes http://www.castinggifts.com/shoebronzing Recoating Tarnished objects http://www.collectorssecret.com/images/sprbeforeafter.jpg

  12. 2 H2O O2 + 4 H+ + 4 e- More Practical Applications: Photosynthesis Photosystem II 1. Chlorophyll in P680 molecule absorbs light. 2. P680 gives up electrons to a transport chain, becoming positive. 3. Electrons from 2 H2O molecules are given to P680 by a Mn4center. The Mn4 center works becauseMn2+, Mn3+, Mn4+, and Mn5+ areall accessible oxidation states. H2O is a reducing agent! http://www.lbl.gov/Science-Articles/Archive/PBD-water-split.html www.pdphoto.org

  13. Fe2O3 (s) + Al (s) Al2O3 (s) + Fe (l) Railroad trackrepairs More Practical Applications: Thermite Reaction UnderwaterWelding 2 Fe (l) + 3H2O (l) Fe2O3 (s) + 3H2 (g) www.wikipedia.org http://www.pagesbydave.com/divepics/pages/underwater%20welding.html

  14. 2(+3)iron(III) oxide More Practical Applications: Thermite Reaction D Fe2O3 (s) + Al (s) Al2O3 (s) + Fe (l) 0 2(+3) 0 Iron(III) oxide is the oxidizing agent. Aluminum oxide is the reducing agent.

  15. Limits to Redox Reactions What is the oxidation number of S in the following compounds? -2 H2S Which cannot be an oxidizing agent? (reduced) S8 0 H2S – cannot gain more electrons +2 SCl2 Which cannot be a reducing agent? (oxidized) Na2SO3 +4 SO42- – cannot lose more electrons SO42- +6

  16. H2O2 (aq) H2O (l) + O2 (g) 2(-1) -2 2(0) Cr1+ (aq) + Cr3+ (aq) 2 Cr2+ (aq) Disproportionation and Conproportionation These are special types of redox reactions: Disproportionation – One compound decomposes into two oxidation states catalyst H2O2 is BOTH oxidized and reduced! Conproportionation – Two oxidation states become one.

More Related