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Let’s do some acid (and bases) , kids !
1) Arrhenius Model
HF HCl HBrHNO3 HClO4 H2SO4
H2CO3
H3PO4
BASE
NaOH KOH NH4OH Ca(OH)2 Mg(OH)2
Al(OH)3
Fe(OH)3
ACID =H+ donor
=OH- donor
CLASSICAL REACTIONs overview(continued)
ACID + BASE = SALT + WATER
General Arrhenius acid-base reaction:
CLASSICAL REACTIONs (continued)
The `Inconvenient Truth’ about the Arrhenius model: basic salts
EXAMPLE: Na2CO3
(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: Na2CO3 (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
Na3PO4 K2SiO3 NaC2H3O2
Basic salts cannot be rationalized using Arrhenius’ acid/base model
CLASSICAL REACTIONs OVERVIEW (continued)
Bronsted to the rescue…
Young Bronsted…
Swedish 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 after marriage and kids
CLASSICAL REACTIONs (continued)
Bronsted Model of Acids/Bases3 new concepts (see pp 452-453 & 623-6)
Acid=
HF, HCl, HBrHNO3 HClO4 H2SO4 H2CO3
H3PO4
No real change from Arrhenius
proton donor (=H+)
CLASSICAL REACTIONs OVERVIEW(continued)
ARRHENIUS ACIDS = BRONSTED ACIDS
New Concept #1: Follow the protons
BASE=
OH-
CO3-2 ,PO4
-3, C2H3O2-,SiO3
-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:
CO32- + 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
HCO3- + OH-
Conjugate idea is like going drag…Men=acid Women=base
BASE ACIDCONJUGATE ACID
CONJUGATEBASE
Identify `acids’ and bases
BRONSTED’S MODEL OF ACIDS/BASES: New Concept #3a: conjugate
acid/base pairs
CO32- + H-OH
Acid conjugate baseBase 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
HCO3- + OH-
Identify `acid’ and baseIdentify conjugate acid and base
PO43- + HCO3 - HPO4
2- + CO32-
Acid conjugate baseBase conjugate acid
acidbaseconjugate base
conjugateacid
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- DONOR PROTON DONOR
ACID + BASE
SALT + WATER
CONJUGATE ACID + CONJUGATE BASE
In-Class Practice Iding Pieces of Bronsted Acid- Basereactions
Let’s do acid !
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. H2O spontaneously decomposed to OH- and H+ in presence of various salts.
D. Many salts without OH- somehow created OH- in water.
Many sa
lts fo
rmed co
nju...
Spontaneous a
cid+base
r...
H2O spontaneously
dec...
Many sa
lts w
ithout O
H-...
25% 25%25%25%
Which part of the Bronsted salt K3PO4 is the proton acceptor ?
A. K+
B. O2-
C. P3-
D. PO43-
E. K3PO4
F. OH-
K+O2-
P3-
PO43-
K3PO4OH-
17% 17% 17%17%17%17%
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.
The anionic part
of salts
...
Spontaneous a
cid/b
ase r.
..
Bronste
d bases a
re pro
to...
Bronste
d acids a
re pro
to...
25% 25%25%25%
In-class reaction Jeopardy
Low heat, precipitates, cation swap metathesis
WHAT IS…
Na2CO3 for example A Bronsted baseWhat’s my reaction type:
HCl + KOH KCl + H2O
Acid/base neutralization (Arrhenius)
Pick the Arrhenius acids
H2O HNO3 NaHCO3 HBr NaCl HNO3 HBr
In-class reaction JeopardyWHAT IS…
What’s my reaction type:K3PO4 + H2O HK2PO4 + KOH
Acid/base hydrolysis(Bronsted)
Write my products ?
AgNO3(aq) + NaCl(aq) ?AgCl(s) + NaNO3(aq)
Pick the Bronsted base(s)
NaOH HBr NaHCO3 K3PO4
NaOH NaHCO3 K3PO4
Pick the Arrhenius basesNaOH
OXIDATION-REDUCTION (REDOX) REACTIONS
see pages text 458-466
REDOX REACTIONS ALL INVOLVE CHANGES IN ELECTRON OWNERSHIP
EXAMPLE #1: (w/demo)
Mgo + 2H+ Mg2+ + H2
0 +2
+1 0
Mg loses 2 e-
Each H+ gains 1 e-
Losing is oxidation
Gaining is reduction
Leo-GerLose electrons = oxidationGain electrons =reduction
Oxidation-Reduction:Remembering which is which…..
Oil-RigOxidation is losing Reduction is gaining
Oxidation-Reduction:Remembering which is which…..
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…)
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 #
H2 O2 N2 Fe Cu Au 0 0 0 0 0 0
To emphasize, metals often written Mo
Example: Fe Feo
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- Co3+ H+ S2-
-1 +3 +1 -2
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
NaF HCl NCl3 SiOF2
-1 -1 -1* -1*
* Each atom of Cl or F is -1
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
H2O NaOH K2CrO4 NaMnO4
-2 -2 -2* -2*
* Each atom of O in compound is -2
HOOH =H2O2
-1 -1PEROXIDE STRUCTURE
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)
HCl NH3 H2O CH4
+1 +1* +1* +1*
*Each H in the compound is +1
PRACTICE ASSIGNING OXIDATION #
N2
O2
H2OFe2O3
H2SO4
N=0O=0H=+1 O= -2Fe=+3 O= -2H= +1 O= -2 S=+6
Provide oxidation # for all elements below