Chapter 7 Chemistry Notes

The element that becomes more positive is oxidized for

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Unformatted text preview: dized. The element that become more negative is reduced. For example: Cu2+ (aq) + 2 e- Cu (s). Copper(II) ions gain electrons and are therefore reduced. Zn (s, metal) + 2 HCl(aq) H2(g) + 2 ZnCl2(aq) Oxidation-Reduction (REDOX) Reactions Metal Oxidation 4 Fe(s) + 3 O2(g) 2 Fe2O3 Oxidized Reduced Hematite, “a rust” Pb + S PbS Oxidized Reduced Galena Notice the atoms, synthesis pattern: A + B AB. Combustion (of carbon and hydrocarbons) C + O2 CO2 Oxidized Reduced Carbon dioxide OIL-Oxidation Is Loss RIG-Reduction Is Gain C3H8 + 5 O2 3 CO2 + 4 H2O Propane oxidized Oxygen reduced Oxidation – electrons are lost Reduction – electrons are gained (more neg. is reduced) Looking Ahead (to chapter 16) This is an example of the oxidation of an organic aldehyde to an organic acid (beyond the scope of this chapter) But the transformation of Ag+ ion to Ag(s) points to a redox reaction. Oxidation-Reduction (REDOX) Reactions Domain of electron transfer reactions - Rust Notice that many redox - Bleach reactions relate to energy - Combustion production, storage, and use. - Batteries (hint-hint: They’re important.) - Fuel Cells - Citric acid cycle - Photosynthesis - Solar Cells and much more -Remember: In these reactions electrons transfer between species Notice the atom exchange pattern: A + BC B + AC. This is an example of (1) a single displacement reaction and (2) gas forming reactions (3) Redox. Ag+(aq) + glucose (aq) Ag(s) + organic acid (aq) Notice you must be able to assign the charge to elements (zero charge) and ions to be able to tell what happens. Notice the atom exchange pattern: A + BC B + AC. This is an example of a single displacement reaction. Electrons can be transferred through wires instead of directly reaction in a solution. This makes batteries possible. Electrolytic and Fuel Cells A hydrogen fuel cell can be used to power an electrical device using the reaction: 2H2 + O2 → 2H2O. ( 2 H2 (g) → 4H+ + 4 e- and O2 + 4 e- → 2 O2-) How can hydrogen be obtained for this reaction? By using a battery, electrons can be “pushed” to transfer in the other direction. This drives the reaction: 2H2O → 2H2 + O2. Notice the pattern of atoms, decomposition: AB A + B 9 9/27/2013 “Clean Energy” Hydrogen generation through electrolysis of water. Types of Reactions (Chem/Physical) Hydrogen use (powering a fan) using a hydrogen fuel cell. 2H2O → 2H2 + O2 2H2 + O2 → 2H2O Classes of Reactions (atom transfer pattern) Synthesis (Combination) (Make stuff) A + B AB Decomposition (Destroy stuff) AB A + B Single Displacement A + BC AC + B Double Displacement AB + CD AD + CB • • • • Precipitation – Formation of solid (↓) drives reactions Acid-Base – Formation of H2O and salt drives reactions Gas Evolution – Formation of gas(↑) drives reactions Oxidation-Reduction (Redox) – Release of energy on electron (e) transfer drives reactions Classify the following by chemical and atom transfer categories: 3 Mg(s) + 2 FeCl3(aq) → 3 MgCl2(aq) + 2 Fe(s) oxidation-reduction, single displacement. 2 HCl(aq) + Na2CO3(aq) → H2CO3(aq) + 2 NaCl(aq) acid-base, double displacement. H2CO3(aq) → CO2(g) + H2O(ℓ) gas forming, decomposition 2 KOH(aq) + FeSO4(aq) → K2SO4(aq) + Fe(OH)2(s) precipitation, double displacement C(s) + O2(g) → CO2(g) oxidation reduction, combustion, synthesis. Summary of Chapter 7 Soluble Li+, Na+, K+, NH4+ NO3-, C2H3O2Cl-, Br-, I- (except Hg22+, Ag+, Pb2+) SO42(except Group 2A & Pb2+) Mostly Insoluble Evidence of Chemical Rxns Chemical Equations Balancing Equations Predicting Chemistry (i.e. ppt) Precipitation – Formation of ↓ drives reactions Acid-Base – Formation of H2O and salt drives reactions Gas Evolution – Formation of ↑ drives reactions Oxidation-Reduction (Redox) Classes of Reactions CO32- , PO43OH- (slightly soluble Group 2A) S2- (except Group 2A) Solubility Rules Acids/bases Types of Reactions (Except Li+, Na+, K+, NH4+, H+) Synthesis (Combination) (Make stuff) Decomposition (Destroy stuff) Single Displacement Double Displacement I surrender A + B AB AB A + B A + BC AC + B AB + CD AD + CB Finish MC7 and skim chapter 8 for Monday. 10...
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