The `Inconvenient Truth’ about the Arrhenius model: basic salts EXAMPLE: Na 2 CO 3 (sodium carbonate ) No H + or OH - ….=> salt only CLASSICAL REACTIONs OVERVIEW continued)

The `Inconvenient Truth’ about the Arrhenius model: basic salts (continued) Turns pink in presence of phenolphthalein gas-forming reaction with HCl, pink disappears experimental results of adding to water: EXAMPLE: Na 2 CO 3 (sodium carbonate) => A base !!!!????? Where’s OH ??? CLASSICAL REACTIONs OVERVIEW(continued)

The `Inconvenient Truth’ about the Arrhenius model: basic salts (continued) Other examples of `basic’ salts Na 3 PO 4 K 2 SiO 3 NaC 2 H 3 O 2 Basic salts cannot be rationalized using Arrhenius’ acid/base model CLASSICAL REACTIONs OVERVIEW (continued)

Bronsted to the rescue… Young Bronsted…Swedis h chemist circa 1910… Young James Dean…American actor circa 1955 …(“Rebel Without a Cause,”“East of Eden”, “Giant” ) Winner of the Bronsted look alike contest…. Bronsted a few years after marriage and kids CLASSICAL REACTIONs (continued)

Bronsted Model of Acids/Bases 3 new concepts (see p. 654) Acid= HF, HCl, HBr HNO 3 HClO 4 H 2 SO 4 H 2 CO 3 H 3 PO 4 No real change from Arrhenius proton donor (=H + ) CLASSICAL REACTIONs OVERVIEW(continued) ARRHENIUS ACIDS = BRONSTED ACIDS New Concept # 1: Follow the protons

BASE= OH - CO 3 -2,PO 4 -3, C 2 H 3 O 2 -,SiO 3 -2 … proton acceptor CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES: New Concept #1: following the protons (cont.) The set of Bronsted bases includes Arrhenius bases + …. … nearly any negative ion (=anion) that even weakly attracts protons Examples of Bronsted Bases

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

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

CO H-OH Acid  conjugate base Base  conjugate acid Base Acid Conjugate acid Conjugate base CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES: New Concept #3a: conjugate acid/base pairs  HCO OH - Identify `acid’ and base Identify conjugate acid and base

PO HCO 3 -  HPO CO 3 2- Acid  conjugate base Base  conjugate acid acid base conjugate base conjugate acid new concept #3a: Conjugates (continued) When acid and base reacts…. EXAMPLE: IDENTIFY ACID, BASE AND THEIR CONJUGATE BASE AND ACID ABOVE

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

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

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.

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 -

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.

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

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

OXIDATION-REDUCTION (REDOX) REACTIONS see pages text REDOX REACTIONS ALL INVOLVE CHANGES IN ELECTRON OWNERSHIP EXAMPLE #1 : Mg o + 2H +  Mg 2+ + H Mg loses 2 e - Each H+ gains 1 e- Losing is oxidation Gaining is reduction