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More In-Class Practice Reviewing Bronsted Acid- Base Concepts Let’s do acid !
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What observation required Bronsted to create a new Acid/Base Theory different than Arrhenius’s model ? A.Many salts formed conjugate acids. B.Spontaneous acid+base reactions only occurred if weaker acids and bases formed. C.H 2 O spontaneously decomposed to OH- and H+ in presence of various salts. D.Many salts without OH - somehow created OH - in water.
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Which part of the Bronsted salt K 3 PO 4 is the proton acceptor ? A.K + B.O 2- C.P 3- D.PO 4 3- E.K 3 PO 4 F.OH -
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What new concept of Bronsted’s most directly explains why many salts are bases? A.The anionic part of salts can hydrolyze water. B.Spontaneous acid/base reactions lead to weaker conjugate acids/bases. C.Bronsted bases are proton acceptors. D.Bronsted acids are proton donors.
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In-class reaction Jeopardy Low heat, precipitates, cation swap metathesis WHAT IS… Na 2 CO 3 for example A Bronsted base What’s my reaction type: HCl + KOH KCl + H 2 O Acid/base neutralization (Arrhenius) Pick the Arrhenius acids H 2 O HNO 3 NaHCO 3 HBr NaCl HNO 3 HBr
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In-class reaction Jeopardy WHAT IS… What’s my reaction type: K 3 PO 4 + H 2 O HK 2 PO 4 + KOH Acid/base hydrolysis (Bronsted) Write my products ? AgNO 3 (aq) + NaCl(aq) ? AgCl(s) + NaNO 3 (aq) Pick the Bronsted base(s) NaOH HBr NaHCO 3 K 3 PO 4 NaOH NaHCO 3 K 3 PO 4 Pick the Arrhenius bases NaOH
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OXIDATION-REDUCTION (REDOX) REACTIONS see pages text 458-466 REDOX REACTIONS ALL INVOLVE CHANGES IN ELECTRON OWNERSHIP EXAMPLE #1 : (w/demo) Mg o + 2H + Mg 2+ + H 2 0+2 +10 Mg loses 2 e - Each H+ gains 1 e- Losing is oxidation Gaining is reduction
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Leo-Ger Lose electrons = oxidation Gain electrons =reduction Oxidation-Reduction: Remembering which is which…..
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Oil-Rig Oxidation is losing Reduction is gaining Oxidation-Reduction: Remembering which is which…..
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Qualitative Features of REDOX Reactions Often involves gross changes in state (solid gas or solution) Extreme changes in energy (fire, light, explosions) prime engine of living metabolisms (if you breathe, you redox…)
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How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS RULES: (SEE PAGE 171 TABLE 4.2) 1) PURE UNCHARGED ELEMENTS HAVE 0 OXIDATION # H 2 O 2 N 2 Fe Cu Au 0 0 0 0 0 0 To emphasize, metals often written M o Example: Fe Fe o
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How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS RULES: (SEE PAGE 171 TABLE 4.2) 2) OXIDATION # OF A CHARGED ATOM IS THE CHARGE ITSELF F - Co 3+ H + S 2- +3+1-2
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How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS RULES: (SEE PAGE 171 TABLE 4.2) 3) F (AND USUALLY THE OTHER HALOGENS) ARE -1 in binary and larger compounds NaFHClNCl 3 SiOF 2 -1 -1 -1 * -1 * * Each atom of Cl or F is -1
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How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS RULES: (SEE PAGE 171 TABLE 4.2) 4) O IS -2 EXCEPT IN PEROXIDES (X-OO-Y) WHERE IT IS -1 H 2 ONaOHK 2 CrO 4 NaMnO 4 -2-2 -2* -2* * Each atom of O in compound is -2 HOOH =H 2 O 2 -1 -1 PEROXIDE STRUCTURE
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How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS RULES: (SEE PAGE 171 TABLE 4.2) 5)H IS +1 FOR COVALENT COMPOUNDS (AND MOST IONIC ONES TOO) HClNH 3 H 2 O CH 4 +1 +1* +1* +1* *Each H in the compound is +1
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PRACTICE ASSIGNING OXIDATION # N2N2 O2O2 H2OH2O Fe 2 O 3 H 2 SO 4 N=0 O=0 H=+1 O= -2 Fe=+3O= -2 H= +1 O= -2 S=+6 Provide oxidation # for all elements below
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Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) 2Al(s) + 3CuSO 4 (aq) Al 2 (SO 4 ) 3 (aq) + 3 Cu(s) Which element oxidized ? Which element reduced ? Which element oxidized ? Which element reduced ? 0 +1 -1 +2 -1 0 0 +2 +6 -2 +3 +6 -2 0 PRACTICE ASSIGNING OXIDATION #(cont.) Mg H Al Cu w/demo
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What are the oxidation # for H, Mn and O in HMnO 4 A.H=+1, Mn=+3, O=-1 B.H=+1, Mn =+7, O=-2 C.H=0, Mn=8, O =-2 D.H=-1, Mn = 9, O=-2
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What is oxidized and reduced in the reaction: PbO + CO Pb+CO 2 A.O reduced, Pb oxidized B.C reduced, Pb oxidized C.Pb reduced, O oxidized D.Pb reduced, C oxidized
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What is oxidized and reduced in the reaction: CH 4 +O 2 CO 2 +H 2 O A.C oxidized, O reduced B.H oxidized, C reduced C.C oxidized, H reduced D.O oxidized. C reduced
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SPECTACULAR REDOX REACTION BEHAVIOR 2Al o (s) + Fe 2 O 3 (s) 2Fe 0 (liq)+Al 2 O 3 (s) 3)let’s see the reaction in the `flesh’ 0 +3-2 0 +3 -2 Which element oxidized ? Which element reduced ? Al Fe 1)assign oxidation # 2) Who does what? 1) Thermite reaction https://www.youtube.com/watch?v=qqvQwfH_ wGQ
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SPECTACULAR REDOX REACTION BEHAVIOR (continued) Example 2: Combustion CH 4 +2O 2 CO 2 +2H 2 O 1) Assign Oxidation # -4 +1 0 +4 -2 +1 -2 Which element oxidized ? Which element reduced ? 2) Who does what? C O BURN BABY, BURN
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: 2Na + Cl 2 NaCl (table salt) SPECTACULAR REDOX REACTION BEHAVIOR (continued) Example 3: Combination redox 1) Assign Oxidation # 0 0 +1 -1 Which element oxidized ? Which element reduced ? 2) Who does what? 3) Let’s see it
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C 12 H 22 O 11 + 8K Cl O 3 11H 2 O + 12CO 2 + 8KCl 4) EXAMPLE 4 Decomposition redox: aka The DEATH TO SKITTLES REACTION SPECTACULAR REDOX REACTION BEHAVIOR (continued) 0 +1 -2 +1 +7 -2 +1 -2 +4 -2 +1 -1 Ox Red And now, the dangerous, scary In-class demo…
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One other unique and highly useful feature of redox reactions … The oxidation and reduction can be separated in space and you can still run the reaction as a `cell’ or ‘battery’
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Example: Cu-Mg cell Cu 2+ + Mg o Cu o +Mg 2+ The complete redox reaction Reduction half reaction: Cu 2+ +2e - Cu o cathode Oxidation half reaction: Mg o Mg 2+ +2e- Gains 2e - Loses 2e- anode Cu 2+ + Mg o Cu o +Mg 2+
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The experimental set-up of (Mg|Mg 2+ ||Cu 2+ |Cu) cell anode cathode LOAD Electron flow out of anode OxidationReduction Mg 0 Mg 2+ +2e - Cu 2+ +2e - Cu o NaCl bridge Na + Cl -
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Traditional demo Potato clock
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