1 May 21 - Chapter 17 textbook OXIDATION-REDUCTION Objective :To determine O.N. for atoms in elements and compounds.HW : Complete worksheet. STUDY PAGE from textbook
2 DO NOW OBSERVATION SKILLS! In your notebook record the experiment in words and then describe the experiment like a chemist (with a CHEMICAL REACTION! )
3 Indicate the metal and the non metal How metals react?How non metals react?Review : draw the dot diagram for each element, and for the compound formedHow many electrons and protons in each reactant?How many electrons and protons in each element in the product?
4 REDOX REACTIONS (electron transfer reactions) Whenever an atom loses an electron another atom has to gain one. Both reactions are simultaneous.Mg + O2 MgOMagnesium lost 2 electrons because oxygen took them. The metal LOST electrons, the NON METAL GAINED electrons
8 REDOX REACTIONS REDuction – OXidation reactions Electrons are transferred from the element that is being oxidized to the one that is being reduced.
9 Oxidation Number (O.N.)Chemist use the O.N. to determine how many electrons are either gained or lost by an atom or ion in a chemical reaction.O.N. is the charge or partial charge of an atom in a compound or an ion.
10 RULES FOR ASSIGNING O.N.1. For all uncombined elements O.N. = O (FREE ELEMENTS)2. For monoatomic ions the charge equals O.N.3. Metals of group 1 in compounds O.N.= +1.Metals of group 2 in compounds O.N.= +2
11 4. Fluorine in compounds is always – 1. Other halogens -1 in binary compounds with metals.5. Hydrogen + 1 except in metal hydrides (combined with metals of group 1 or 2)6. Oxygen is -2 except when combined with F (is =2) or in peroxides (-1).
12 7. THE SUM OF THE OXIDATION NUMBERS IN ALL COMPOUNDS MUST BE ZERO 8. FOR POLYATOMIC IONS THE SUM OF THE O.N. IS EQUAL TO THE CHARGE OF THE ION
13 Group workGet in your groups and practice what you just have learnt and complete handout.Finish the rest for homework.
14 Answer to finding the Oxidation state +7+5+4+6+2+3+5+6
15 Review Find the O.N. for each element Cl2K2S2O3NO3-PO43-CaCr2O7KNO2OF2H2O2KH
16 May 22Objective: How to keep track of electron transfers in chemical reactions?HW: finish worksheet and read page 604 to 605.Answer question 1 from page 611
17 DO NOW OBSERVATION SKILLS! In your notebook record the experiment in words and then describe the experiment like a chemist (with a CHEMICAL REACTION! )
18 PRACTICE HCl + Mg -> MgCl2 + H2 Indicate the oxidation state of each element in the reaction.READ HANDOUT “ANALYZING OXIDATION-REDUCTION REACTIONS”
19 VOCABULARY SIMULTANEOUS = at the same time OXIDATION = to lose electronsREDUCTION = to gain electronsOXIDATION NUMBER = charge or partial charge over an element.
20 To recognize redox reactions… Look for changes in the oxidation number or the atoms. If one element changed the O.N. then for SURE is redox reaction.All single replacement, synthesis, decomposition and combustion reactions are REDOX.Double replacement reactions are not redox.
21 PRACTICE – your turn!Get in your group and work with the reactions in the handout. Determine the O.N. for each element and decide which element got oxidized and which got reduced (TIP ALWAYS IN THE REACTANTS SIDE!!!)
22 May 24 How to recognize oxidizing and reducing agents? How to separate a redox reaction into half reactions?
23 AGENTSThey are always found in the reactants side.
24 REDUCING AGENT When a substance is oxidized it LOSES electrons. Its O.N. increases. It is being oxidized and is making the other substance in the reaction reduced. Then the one that gets oxidized is the REDUCING AGENT.R.A. gets oxidized.Its O.N. increasesActive metals are good RA
25 OXIDIZING AGENTS When a substance is reduced it GAINS electrons . Its O.N. decreases. It is being reduced, it takes electrons from the other specie, it makes the other specie to get oxidize.The one that gets reduced is the OXIDIZING AGENTOxidizing Agent : Gets reducedIts ON decreases.
26 2Mg + O2 MgOMg: oxidation number changes from0 to +2 . It increased.Mg gets oxidized. Is the reducing agent.Oxygen: Oxidation number changes from 0 to -2 , it decreases is the Oxidizing agent.
27 Half reactionsHw p 164 q 32 to 36And finish worksheet #3
28 Half reactionsA redox reaction can always be broken down as 2 half reactions that show the atom or ion that is being oxidized and the one that is being reduced.MASS AND CHARGE has to be conserved in a half reaction1. find the o.n. of each element in the reaction. Determine which is being reduced an which is being oxidized
29 2. Balance the masses first 3. Complete each half reaction with electrons.( LEO GER)4. Verify that masses and charges are balanced.
30 May 28 Objetive: Spontaneous Redox Reaction To use table J to predict if a single replacement reaction will occurr.
31 Activity series Spontaneous Reactions : happen without external help. CuSO4 + Zn Zn SO4 + CuIn a single replacement reaction the most active element replaces the other element from a compound. (TABLE J)
32 Table J The metal above gets oxidized the one below will get reduced. For non metals the one above gets reduced the one below gets oxidized.
34 METALS IN TABLE JThe higher the metal is in table J, the most active it is, the more tendency to became oxidized (lose electrons)On Top of table J best reducing agentsTowards the bottom metals tend to gain electrons then they became reduced and are good reducing agents
35 Non MetalsF2 has the greatest tendency to gain electrons ( became reduced) is the BEST OXIDIZING AGENT.
36 Predict if the reaction will occur Ag (NO3) + Cu Zn+2 + Co MgCl2 + Ni K + FeCl3 Li + Mg 2+
37 May 29 ELECTROCHEMISTRYOBJECTIVE: To distinguish between electrochemical and electrolytic cellsTo identify the different parts of a cell and explain their purpose.
38 Do now What SPONTANEOUS reaction would occur if we have Cu, Cu2+, Zn and Zn2+ together.Hint USE TABLE JWhere the electrons flow? Which loses which gains?
39 Voltaic CellsIn spontaneous oxidation-reduction (redox) reactions, electrons are transferred and energy is released.
40 IDEA!If we can place the two metals in two different containers and connect them with a wire the electrons will flow from the Zn to the Cu and we will have an electric current – ELECTRICITYBut it does not work if we do not close the circuit – USE A SALT BRIDGE
41 Voltaic Cells A typical cell looks like this. The oxidation occurs at the anode.The reduction occurs at the cathode.
42 ELECTRODESWhere the reduction or oxidation takes place. They are usually metals or they can be made of graphite.RED CATREDuction at the cathode
43 ELECTROCHEMISTRY *Anode: where the oxidation occurs. *Cathode: where the reduction occurs.Voltaic or galvanic cell: produce ELECTRICITY from an spontaneous chemical reaction.
44 ELECTRON FLOW. FROM THE ONE THAT GETS OXIDIZED TO THE ONE THAT GETS REDUCED. POLARITIESANODE – NEGATIVE source of electronsCATHODE- POSITIVE
45 REDuction at the cathode A typical voltaic cellRED CATREDuction at the cathodeCathode: the electrode at which reduction occursAnode: the electrode at which oxidation occursSalt bridge: a tube containing strong electrolyte, a pathway to allow the ions to move from one side to another. PERMIT THE MIGRATION OF IONS
46 Problems1. A cell uses the reaction Mn + Ni2+ Ni + Mn2+ to produce electricity.Write the half-reaction that occurs at the anode.b) Write the half-reaction that occurs at the cathode.c) Which species in this cell loses electrons?d) As the cell produces electricity, which ion increases in concentration?Mn Mn2+ + 2e-Ni2+ + 2e- NiMnMn2+
47 1. Voltaic CellA type of electrochemical cell that converts chemical energy to electrical energy by a spontaneous redox reaction.In 1800, Volta built the voltaic pile and discovered the first practical method of generating electricity. Constructed of alternating discs of zinc and copper, with pieces of cardboard soaked in salt water b/w the metals, the voltaic pile produced electrical current.
48 Electrochemical cellAn apparatus that uses a redox reaction to produce electrical energy (voltaic cell) or uses electrical energy to cause a chemical reaction (electrolytic cell).
49 Electrolysis: to decompose a substance using electricity Electrolytic cellUses electricity to force a reaction that is not spontaneous to occur.NOTICE THAT IN ELECTROLYTIC CELLS THERE IS A BATTERY OR A POWER SOURCE PRESENTElectrolysis: to decompose a substance using electricity
51 ElectroplatingIs used to cover an object with metal using electricity.THE OBJECT TO BE COVERED GOES IN THE CATHODEPOLARITIES : ANODE – POSITIVECATHODE- NEGATIVE SOURCE OF ELECTRONS – CONNECTED TO NEGATIVE