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Bronsted Acid/Base Concepts and Redox Reactions Overview

This overview covers the Bronsted model of acids and bases, including new concepts such as following the protons, hydrolysis reactions, and conjugate acid/base pairs. It also introduces the basics of oxidation-reduction (redox) reactions.

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Bronsted Acid/Base Concepts and Redox Reactions Overview

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  1. Exam 2 Wednesday 4/4 Homework 9 posted and due Monday 4/2

  2. CLASSICAL REACTIONs OVERVIEW(continued) BronstedModel of Acids/Bases3 new concepts (see pp 452-453 & 623-6) New Concept #1: Follow the protons Acid= proton donor (=H+) No real change from Arrhenius HF, HCl, HBr HNO3 HClO4 H2SO4 H2CO3 H3PO4 ARRHENIUS ACIDS = BRONSTED ACIDS

  3. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:New Concept #1: following the protons (cont.) BASE= proton acceptor Examples of Bronsted Bases OH- CO3-2 ,PO4-3, C2H3O2-,SiO3-2… The set of Bronsted bases includes Arrhenius bases + …. …nearly any negative ion (=anion) that even weakly attracts protons

  4. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:New Concept #2 How the proton acceptor creates the basic salt effect: Hydrolysis…Bronsted bases `split’ water !!! EXAMPLE CO32- + H-OH  HCO3- + OH- Hydrolysis reaction ..Bronsted Base is basic in water because it splits water to make OH-!

  5. BRONSTED’S MODEL OF ACIDS/BASES:New Concept #3a: conjugate acid/base pairs Conjugate idea is like going drag… Men=acid Women=base Identify `acids’ and bases CONJUGATE ACID CONJUGATE BASE BASE ACID

  6. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:New Concept #3a: conjugate acid/base pairs Identify `acid’ and base Identify conjugateacid and base Conjugate acid  HCO3- + OH- CO32- + H-OH Acid Base Conjugatebase Acid conjugate base Base conjugate acid

  7. new concept #3a: Conjugates (continued) When acid and base reacts…. Acid conjugate base Base conjugate acid EXAMPLE: IDENTIFY ACID, BASE AND THEIR CONJUGATEBASE AND ACID ABOVE PO43- + HCO3- HPO42- + CO32- CONJUGATE ACID CONJUGATE BASE BASE ACID

  8. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:New Concept #3b: Bronsted Model ACID + BASE CONJUGATE BASE + CONJUGATE ACID • spontaneous acid + base reactions produce weaker acids + bases Contrast to Arrhenius Model ACID + BASE SALT +WATER Both products `neutral’

  9. ACID-BASE THEORIES SUMMARIZED ARRHENIUS BRONSTED PROTON DONOR ACID = H+DONOR BASE= OH- DONOR PROTONDONOR ACID + BASE SALT + WATER CONJUGATE ACID + CONJUGATE BASE

  10. What observation required Bronsted to create a new Acid/Base Theory different than Arrhenius’s model ? • Many salts formed conjugate acids. • Spontaneous acid+base reactions only occurred if weaker acids and bases formed. • H2O spontaneously decomposed to OH- and H+ in presence of various salts. • Many salts without OH- somehow created OH- in water.

  11. Which part of the Bronsted salt K3PO4 is the proton acceptor ? • K+ • O2- • P3- • PO43- • K3PO4 • OH-

  12. What new concept of Bronsted’s mostdirectly explains why many salts are bases? • The anionic part of salts can hydrolyze water. • Spontaneous acid/base reactions lead to weaker conjugate acids/bases. • Bronsted bases are proton acceptors. • Bronsted acids are proton donors.

  13. In-class reaction Jeopardy WHAT IS… Low heat, precipitates, cation swap metathesis Pick the Arrhenius acids H2O HNO3 NaHCO3 HBr NaCl HNO3 HBr Na2CO3 for example A Bronsted base What’s my reaction type: Acid/base neutralization (Arrhenius) HCl + KOH KCl + H2O

  14. In-class reaction Jeopardy WHAT IS… What’s my reaction type: Acid/base hydrolysis (Bronsted) K3PO4 + H2O  HK2PO4 + KOH Write my products ? AgNO3(aq) + NaCl(aq) ? AgCl(s) + NaNO3(aq) Pick the Bronsted base(s) NaOH NaHCO3 K3PO4 Pick the Arrhenius bases NaOH NaOH HBr NaHCO3 K3PO4

  15. Still want more practice with Acid/Base and Metatheses ????

  16. OXIDATION-REDUCTION (REDOX) REACTIONS REDOX REACTIONS ALL INVOLVE CHANGES IN ELECTRON OWNERSHIP EXAMPLE #1: (w/demo) +1 0 Mgo+ 2H+ Mg2++ H2 0 +2 Mg loses 2 e- Losing is oxidation Each H+ gains 1 e- Gaining is reduction

  17. Oxidation-Reduction: Remembering which is which….. Leo-Ger Lose electrons = oxidation Gain electrons =reduction

  18. Oxidation-Reduction: Remembering which is which….. Oil-Rig Oxidation is losing Reduction is gaining

  19. 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…)

  20. How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS 1) PURE UNCHARGED ELEMENTS HAVE 0 OXIDATION # 0 0 0 0 0 0 H2 O2 N2 Fe Cu Au To emphasize, metals often written Mo Example: Fe  Feo

  21. How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS THE RULES: (continued) 2) OXIDATION # OF A CHARGED ATOM IS THE CHARGE ITSELF -1 +3 +1 -2 F- Co3+ H+ S2-

  22. How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS THE RULES: (continued) 3) F (AND USUALLY THE OTHER HALOGENS) ARE -1 in binary and larger compounds -1 -1 -1* -1* NaF HCl NCl3 SiOF2 * Each atom of Cl or F is -1

  23. How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS THE RULES: (continued) 4) O IS -2 EXCEPT IN PEROXIDES (X-OO-Y) WHERE IT IS -1 -2 -2 -2* -2* H2O NaOH K2CrO4 NaMnO4 * Each atom of O in compound is -2 -1 -1 PEROXIDE STRUCTURE HOOH =H2O2

  24. How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS THE RULES: (continued) 5)H IS +1 FOR COVALENT COMPOUNDS (AND MOST IONIC ONES TOO) +1 +1* +1* +1* HCl NH3 H2O CH4 *Each H in the compound is +1

  25. Oxidation # RULES SUMMARIZED 1) PURE UNCHARGED ELEMENTS HAVE 0 OXIDATION # 2) OXIDATION # OF A CHARGED ATOM IS THE CHARGE ITSELF • F (AND USUALLY THE OTHER HALOGENS) ARE • -1 IN BINARY AND LARGER COMPOUNDS 4) O IS -2 EXCEPT IN PEROXIDES (X-OO-Y) WHERE IT IS -1 5) H IS +1 FOR COVALENT COMPOUNDS (AND MOST IONIC ONES TOO)

  26. PRACTICE ASSIGNING OXIDATION # Provide oxidation # for all elements below N2 O2 H2O Fe2O3 H2SO4 N=0 O=0 H=+1 O= -2 Fe=+3 O= -2 H= +1 O= -2 S=+6

  27. PRACTICE ASSIGNING OXIDATION #(cont.) 0 +1-1 +2 -1 0 Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) Zn Which element oxidized ? w/demo Which element reduced ? H 0 +2 +6 -2 +3 +6 -2 0 2Al(s) + 3CuSO4(aq) Al2(SO4)3(aq) + 3 Cu(s) Al Which element oxidized ? w/demo Cu Which element reduced ?

  28. What are the oxidation # for H, Mn and O in HMnO4 • H=+1, Mn=+3, O=-1 • H=+1, Mn =+7, O=-2 • H=0, Mn=8, O =-2 • H=-1, Mn = 9, O=-2

  29. What is oxidized and reduced in the reaction: PbO + COPb+CO2 • O reduced, Pb oxidized • C reduced, Pb oxidized • Pb reduced, O oxidized • Pb reduced, C oxidized

  30. In the reaction: CH4+2O2 CO2+2H2Othe oxidation # for reactant C vs. product C and reactant O vs. product O are: C ; O • +4 vs. -4; 0 vs. +2 • 0vs. +4; -2 vs. +2 • -4vs. +4; 0 vs. +2 • -4 vs.+4; 0 vs. -2

  31. What is oxidized and reduced in the reaction: CH4 +2O2CO2 +2H2O • C oxidized, O reduced • H oxidized, C reduced • C oxidized, H reduced • O oxidized. C reduced

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