Chemistry Chapter 20-21 Acids and Bases. Acid-Base Theories TheoryAcidBase Arrhenius HC2H3O2HC2H3O2...
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Transcript of Chemistry Chapter 20-21 Acids and Bases. Acid-Base Theories TheoryAcidBase Arrhenius HC2H3O2HC2H3O2...
Chemistry Chapter 20-Chemistry Chapter 20-2121
Acids and BasesAcids and Bases
Acid-Base TheoriesAcid-Base Theories
Theory Acid Base
Arrhenius
HC2H3O2
Produces H+
ions in solution HCl
Produces OH-
ions in solution NaOH Ca(OH)2
Acid-Base TheoriesAcid-Base TheoriesTheory Acid Base
Bronsted-Lowry
Proton (H+ ion) donor.
Proton (H+ ion) acceptor.
Includes more molecules that do not have OH-
NH3 (ammonia)Conjugate Acid-Base Pairs
NH3 + HOH HOH + OH-NH4+
Acid(proton donor)
Base(conjugate base)proton acceptor
Acid(Conjugate acid)
proton donor
Base(proton acceptor)
Ionization of HCl and Ionization of HCl and formation of hydronium ion, formation of hydronium ion,
HH33OO++
H2O + HCl H3O+ + Cl-
Protondonor
Protonacceptor
Hydroniumion
Chlorideion
Acid ConjugateBaseBronsted/Lowry (Acid-Base Pair)
Ionization of HCl and Ionization of HCl and formation of hydronium ion, formation of hydronium ion,
HH33OO++
H2O + HCl H3O+ + Cl-
Protondonor
Protonacceptor
Hydroniumion
Chlorideion
BaseConjugate
AcidAnother Acid-Base Pair
Acids are Proton DonorsAcids are Proton Donors
Monoprotic acidsDiprotic acids Triprotic acids
HCl
HC2H3O2
HNO3
H2SO4
H2CO3
H3PO4
Note: a proton is a hydrogen ion.
“protic” = proton
Bronsted/Lowry Theory = proton donor idea
(All theories agree these are acids)
Acid-Base TheoriesAcid-Base Theories
Theory Acid Base
Lewis (e- pair) acceptor
(e- pair) donor BCl3 NH3
N
H
H
H
B
Cl
Cl Cl
Lewis Acid-Base TheoryLewis Acid-Base Theory
Lewis Acid Lewis Basee- pair acceptor
e- pair donor
Al
NH3 (ammonia)
Cl
Cl
Cl N
H
H
H
AlCl3 (aluminum chloride)
Lewis Acid-Base TheoryLewis Acid-Base Theory
Lewis Acid Lewis Basee- pair acceptor
e- pair donor
NH3 (ammonia)
Al
Cl
Cl
Cl
N
H
H H
AlCl3 (aluminum chloride)
Amphoteric: A substance that can act as an acid or a base.
Water is an example: H2O = HOH
Acid-Base Theories Acid-Base Theories SummarySummary
Theory Acid Base
Arrhenius
HC2H3O2
Produces H+
ions in solution HCl
Produces OH-
ions in solution NaOH Ca(OH)2
Bronsted-Lowry
H+ ion (proton) donor.
H+ ion (proton) acceptor. NH3 (ammonia)
Lewis (e- pair) acceptor
(e- pair) donor BCl3 NH3
HOH HOH
Strong Acid DissociationStrong Acid Dissociation
H+ + H2O H3O+
Hydronium is a result of proton transfer (H+ donated to H2O).
Strong AcidsStrong Acids
Strong acids are assumed to be 100% ionized in solution (good proton donors).
HCl
H2SO4
HNO3
H+ + Cl-
H+ + HSO4-
H+ + NO3-
Arrow in one direction indicatesthat molecule dissociates completely.
Weak AcidsWeak AcidsWeak acids are usually less than 5% ionized in solution (poor proton donors).
H3PO4
HF H+ + F-
H+ + H2PO4-
H2PO4- H+ + HPO4
2-
Double arrow = (Reaction goes both ways)
The larger arrow = (Favored side)
Weak Acid DissociationWeak Acid Dissociation
Weak acids are mostly molecules.(Only 5% or less dissociate)
Acid Dissociation Constant (Weak Acids)
Ka = product concentrations vs. reactant concentrations for weak acids.HF(aq) H3O+
(aq) + F-(aq)H2O(l)+
Ka =
[H3O+
][F-][HF]
H2O not included because it is in a different phase.
Base Dissociation Constant (Weak Bases)
Kb = product concentrations vs. reactant concentrations for weak acids.NH3(aq) NH4
+(aq) + OH-
(aq)HOH(l)+
Kb =
[NH4+
][OH-][NH3]
H2O not included because it is in a different phase.
HX(aq) H+(aq) + X-
(aq)
Ka =[H+] [X-]
[HX]
InitialChange
Equilibrium
0.35 M 0 0
- 0.041 M 0.041 M 0.041 M
0.041 M 0.041 M0.35 – 0.041 = 0.309 M
=(0.041)
0.309
(0.041) = 0.0054
M
Methyl Red changes from red to orange in this range.
Phenolphthalein changes to pink in this range.
HIn(aq) H+(aq) + In-
(aq)
Phenolphthalein Bromthymol blue Methyl Red
(Weakest acid) (Strongest Acid)
H2In(aq) H+(aq) + HIn-
(aq)
HIn-(aq) H+
(aq) + In2-(aq)
The indicator must be a diprotic acid for 2 color changes.
Red to yellow.
Yellow to blue.
Kw = [H+] x [OH-]
Ion-product constant = Hydrogen-ion concentration x hydroxide-ion concentration
Basic, neutral and acidic are all ways of describing pH concentrations in a solution.
The other terms are all associated with bases.
The other terms are related to pH or can be calculated from pH.
The other terms are all acid-base theories.
Conjugate acids and bases are part of Bronsted-Lowry theory.
The other terms describe ionizable hydrogen ions..
Dissociation constants are used with weak acids and bases.
Sulfuric AcidSulfuric Acid
Highest volume production of Highest volume production of any chemical in the U.S.any chemical in the U.S.
Used in the production of Used in the production of paper
Used in production of Used in production of fertilizers
Used in petroleum refiningUsed in petroleum refining
Nitric AcidNitric Acid• Used in the production Used in the production
of fertilizersof fertilizers• Used in the production Used in the production
of of explosives• Nitric acid is a Nitric acid is a volatile
acid – its reactive – its reactive components evaporate components evaporate easilyeasily
• Stains proteins Stains proteins (including skin!)
Hydrochloric AcidHydrochloric Acid• Used in the pickling of Used in the pickling of
steel• Used to purify Used to purify
magnesium from sea magnesium from sea waterwater
• Part of Part of gastric juice, it , it aids in the digestion aids in the digestion of proteinof protein
• Sold commercially as Sold commercially as “Muriatic acid”“Muriatic acid”
Phosphoric Phosphoric AcidAcid
o A flavoring agent in A flavoring agent in sodas
o Used in the Used in the manufacture of manufacture of detergentsdetergents
o Used in the Used in the manufacture of manufacture of fertilizersfertilizers
o NotNot a common a common laboratory reagent reagent
Acetic AcidAcetic AcidUsed in the manufacture Used in the manufacture
of of plasticsUsed in making Used in making
pharmaceuticalspharmaceuticalsAcetic acid is the acid Acetic acid is the acid
present in present in vinegar
Examples of Organic AcidsExamples of Organic Acids
Citric acid in citrus fruitCitric acid in citrus fruit Malic acid in sour applesMalic acid in sour apples Deoxyribonucleic acid, Deoxyribonucleic acid, DNA Amino acids, the building blocks of Amino acids, the building blocks of
proteinprotein Lactic acid in Lactic acid in sour milk and sore and sore
musclesmuscles Butyric acid in rancid butterButyric acid in rancid butter
Weak AcidsWeak Acids: (Organic): (Organic)
HC2H3O2
Organic acids (Acids that contain carbon)are always weak acids.
H+ + C2H3O2-
CH3COOH H+ + CH3COO-
Carboxylic Acid group: R-COOH
Same acid written another way
Organic AcidsOrganic AcidsOrganic acids all contain the “carboxyl” group called “carboxylic acid”, sometimes several of them.
The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.
Properties of BasesProperties of Bases Bases taste bitter Bases effect indicators
Red litmus turns blue Phenolphthalein turns purple
Bases have a pH greater than 7 Bases are proton (hydrogen ion, H+) acceptors Solutions of bases feel slippery Bases neutralize acids
Products of NeutralizationProducts of Neutralization
HCl + NaOH H2SO4 + Ca(OH)2 HNO3 + KOH The products of neutralization are always a ______ and _______.
NaCl + H2O
CaSO4 + 2 H2O
KNO3 + H2O
salt water
Measuring pH with wide-range Measuring pH with wide-range paperpaper
Narrow-Range pH PaperNarrow-Range pH Paper
pH pH IndicatorIndicator
s s and theirand theirrangesranges
Calculating [HCalculating [H++] and [OH] and [OH--]]
Examples:
[H+] = 1 x 10-2pH = 2.0
[H+] = 10-12pH = 12.0
[H+] = 10-4.3 = 5 x 10-5pH = 4.3
[OH-] = 1 x 10-4pOH = 4.0
[OH-] = 1 x 10-8pOH = 8.0
[OH-] = 1 x 10-10pOH = 10.0
Acidic
Basic
Acidic
Basic
Acidic
Acidic
pH=10
pH=6
pH=4
[H+] = 10-pH and [OH-] = 10-pOH
Calculating pH, Calculating pH, pOHpOH
pH = -log[H3O+] or pH = -log[H+]
pOH = -log[OH-]
Relationship between pH and Relationship between pH and pOHpOH pH + pOH = 14
Finding [HFinding [H33OO++], [OH], [OH--] from pH, pOH] from pH, pOH
[H3O+] = 10-pH or [H+] = 10-pH
[OH-] = 10-pOH
SUMMARYSUMMARY
Acids React with Active Acids React with Active MetalsMetals
Acids react with active metals to form salts and hydrogen gas.
Mg + 2HCl MgCl2 + H2(g)
Acids React with CarbonatesAcids React with Carbonates
2HC2H3O2 + Na2CO3
2 NaC2H3O2 + H2O + CO2
Effects of Acid Rain on MarbleEffects of Acid Rain on Marble(calcium (calcium carbonatecarbonate))
George Washington:BEFORE
George Washington:AFTER
Acids Neutralize BasesAcids Neutralize Bases
HCl + NaOH NaCl + H2O
Neutralization reactions ALWAYS produce a salt and water.
Products of NeutralizationProducts of Neutralization (Lab 23)
HCl(aq) + NaOH(aq)
HC2H3O2(aq) + NaOH(aq)
HCl(aq) + NH3 (aq)
NaCl(aq) + H2O(l)
NaC2H3O2 (aq) + H2O(l)
NH4+1
(aq) + Cl-1(aq)
HC2H3O2(aq) + NH3(aq) NH4+1
(aq) + C2H3O2-1
(aq)
Trial 1 (Strong acid and Strong Base)
Trial 2 (Weak acid and Strong Base)
Trial 3 (Strong acid and Weak Base)
Trial 4 (Weak acid and Weak Base)
Titration CurvesTitration Curves
Bases Neutralize Bases Neutralize AcidsAcids
Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl.
2 HCl + Mg(OH)2
MgCl2 + 2 H2O
Titration CalculationsTitration Calculations