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