Warm Up Predict the products and balance the following equations: a. KI + Br2 → b. H2SO4 + KOH → Questions on Activity Series WS? Questions on Word Equations WS? Genie in a Bottle H2O2 + Honors Electrochemistry Electron Transfer Reactions Electron transfer reactions are oxidation-reduction or redox reactions. Result in the generation of an electric current (electricity) or be caused by imposing an electric current. This field of chemistry is often called ELECTROCHEMISTRY. Redox Vocab OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. OXIDIZING AGENT—electron acceptor; species is reduced. REDUCING AGENT—electron donor; species is oxidized. You can’t have one… without the other! Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation GER! LEO the lion says GER! Another way to remember OIL RIG OXIDATION-REDUCTION REACTIONS Direct Redox Reaction Oxidizing and reducing agents in direct contact. Cu(s) + 2 Ag+(aq) → Cu2+(aq) + 2 Ag(s) OXIDATION-REDUCTION REACTIONS Indirect Redox Reaction A battery functions by transferring electrons through an external wire from the reducing agent to the oxidizing agent. Basic Concepts of Electrochemical Cells Anode Cathode CHEMICAL CHANGE ---> ELECTRIC CURRENT To obtain a useful current, we separate the oxidizing and reducing agents so that electron transfer occurs thru an external wire. This is accomplished in a GALVANIC or VOLTAIC http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf cell. A group of such cells is called a battery. Zn --> Zn2+ + 2e- Cu2+ + 2e- --> Cu Oxidation Anode Negative Reduction Cathode Positive <--Anions Cations--> RED CAT •Electrons travel thru external wire. Salt bridge allows anions and cations to move between electrode compartments. Oxidized or Reduced? Oxidation number is assigned to an element in a molecule based on the distribution of electrons in the molecule. Rules for assigning oxidation numbers. The oxidation number of…. 1. 2. 3. 4. 5. 6. 7. 8. Any pure element is 0 Monatomic ion = the charge on the ion More EN element in a binary compound = the number equal to the charge it would have if it were an ion. F = 1O = 2- unless combined with F or is a peroxide H = 1+, unless combined with a metal (1-) Sum of the oxidation numbers in a neutral atom = 0. Polyatomic ion = charge of polyatomic ion Let’s Practice NaOH H2SO3 KNO3 SO2 CaCl2 How can you tell? The atoms or ions of an element experience an increase in oxidation state…oxidation. Na0 → Na1+ + 1eThe atoms or ions of an element experience a decrease in oxidation state… reduced. Cl2 + 2e- → 2Cll- Half-Reaction Represents the part of the reaction undergoing oxidation/reduction. Cu → Cu2+ + 2e2NO3 + 2e- + 4H+ → 2NO2 + 2H2O Not all reactions are Redox SO2 + H2O → H2SO4 Let’s look at the WS… Warm Up- How did you do on the redox WS? Na= +1 K= +1 O = -2 H= +1 O= -2 O = -2 O= -2 Cr=+6 O= -2 C= +4 C = -4 H= +1 Cl= +7 Mn = +4 Electrochemical Cell Lab- Everyone fills in their own lab sheets… turn in recorders Leader/Recorder- Keeps everyone on task, makes sure instructions are being followed carefully. Aides scientist. Reader- Reads every single word out loud… helps others make sense of lab. Scientist- Obtains materials and follows all instructions. Helps others make sense of the lab. Read the Introduction Paragraph as a whole group. Quickly obtain the materials and goggles… get started on this guided inquiry lab. Make sure all names are on the recorders paper… turn in when complete.