Chapter 14Acids & Bases

14.1 Properties of Acids and Bases

Properties of Acids1. Aqueous solutions have a sour taste 2. Some acids react with active metals to release

hydrogen:

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)

3. Acids react with bases to produce salts and water:

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

4. Acids conduct electric current

Properties of Acids5. Acids change the color of acid-base

indicators:

Blue litmus turns red

Methyl orange turns red

6. Have a pH of less than 7

7. Donate protons, H+

8. React with carbonates

9. Neutralize bases

Review: Acids Nomenclature• Binary acids - acids that contain two different

elements: hydrogen and one of the more-electronegative elements • prefix "hydro-" • Root of element name • "-ic" ending

• example: HBr = hydrobromic acid • Oxyacids - compounds of hydrogen, oxygen,

and a third element, usually a nonmetal – no prefixes

Some Common Industrial Acids• Sulfuric AcidHighest volume production

of any chemical in the U.S. Used in the production of

paper, fertilizers, petroleum refining & car batteries

Some Common Industrial Acids

• Nitric Acid• Used in the production of rubber,

plastics, pharmaceuticals, fertilizers & explosives

• Nitric acid is a volatile acid – its reactive components evaporate easily

• Stains proteins yellow (including skin!)

Some Common Industrial Acids• Hydrochloric Acid• Used in the pickling of steel• Used to purify magnesium

from sea water• Used to correct swimming

pool pH• Part of gastric juice, it aids in

the digestion of protein• Sold commercially as

“Muriatic acid”

Some Common Industrial Acids

• Phosphoric Acido A flavoring agent in sodaso Used in the manufacture of

detergents & fertilizerso Not a common laboratory reagent

Some Common Industrial Acids

• Acetic AcidConcentrated “glacial” acetic

acid used in the manufacture of plastics

Used in making pharmaceuticalsAcetic acid is the acid present in

vinegar

Properties of Bases1. Aqueous solutions of bases have a bitter

taste 2. Bases change the color of acid-base

indicators Turns red litmus blueTurns phenolphthalein

magenta/purple3. Dilute aqueous solutions of bases feel

slippery 4. Bases react with acids to produce salts

and water 5. Bases conduct electric current 6. Are proton, H+, acceptors7. Have a pH value of greater than 78. Neutralize acids

Arrhenius Acids & Bases

• Arrhenius Acid A chemical compound that increases the concentration of hydrogen ions, H+, in aqueous solution

• Arrhenius BaseA substance that increases the concentration of hydroxide ions, OH-, in aqueous solution Swedish Chemist

Aqueous Solutions of Acids • Acids are molecular compounds that

ionize in solution

HNO3 + H2O → H3O+ + NO3-

H2SO4 + H2O → H3O+ + HSO4-

H2O + HCl → H3O+ + Cl-

Proton Proton DonorDonor

Proton Proton AcceptorAcceptor

Ionization Equations• Instead of:

HCl (g) + H2O (l) → H3O+ (aq) + Cl- (aq)

• Sometimes we write this:

HA + H2O (l) → H3O+ (aq) + A- (aq)

• Or even this:

HCl (aq) → H+ (aq) + Cl- (aq)

Generic formulas

Leave out water

Strength of Acids• Strong acids completely

ionize in solution. (100%)• Weak acids ionize only

slightly and are weak electrolytes.(<5%)

Strong Acid Dissociation

Weak Acid Dissociation

Strength vs. Concentration

• Strength refers to ionization in solution.

• Concentration refers to the amount of solute in solution.

• It is possible to have a concentrated solution of a weak acid or base.

• It is also possible to have dilute solution of a strong acid or base.

Organic AcidsOrganic acids all contain the “carboxyl” group, sometimes several of them.

The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

Examples of Organic Acids Citric acid in citrus fruit Malic acid in sour apples Deoxyribonucleic acid,

DNA Amino acids, the building

blocks of protein Lactic acid in sour milk

and sore muscles Butyric acid in rancid

butter

Aqueous Solutions of Bases• Ionic bases dissociate when placed in water:

NaOH (s) + H2O (l) → Na+ (aq) + OH- (aq)

• Basic solutions are referred to as “alkaline”• Molecular bases produce hydroxide ions through

a reaction with water:

NH3 (g) + H2O (l) → NH4+ (aq) + OH- (aq)

Strength of Bases

• Strength of ionic bases in related to solubility:

High solubility = strong base

Low solubility = weak base

• Molecular bases tend to be weak regardless of solubility

Chapter 14Acids & Bases

14.2 Acid-Base Theories

Bronsted-Lowry Acids & Bases

• Bronsted-Lowry Acid:

A molecule or ion that is a proton donor• Bronsted-Lowry Base:

A molecule or ion that is a proton acceptor

ex: hydroxide ion is the acceptor portion of the ionic base, not the whole compound itself

• Bronsted-Lowry Acid-Base Reaction:

A reaction in which protons are transferred from the acid to the base.

Types of Acids

• Monoprotic Acids: HC2H3O2

HCl

• Diprotic Acid: H2SO4

• Triprotic Acids: H3C6H5O7

H3PO4

• * Each successive proton is harder to remove!

Can donate 1

H

Can donate 2

Hs

Can donate 3

HsPolyprotic AcidsPolyprotic Acids

Lewis Acids & Bases• Lewis Acid:

An atom, ion or molecule that accepts an electron pair to form a covalent bond

• Lewis Base:An atom, ion or molecule that donates an electron pair to form a covalent bond

• Lewis Acid-Base Reaction:The formation of one or more covalent bonds between an electron-pair donor and electron-pair acceptor. This definition can be applied to phases other than aqueous reactions.

Chapter 14Acids & Bases

14.3 Acid-Base Reactions

Conjugate Acids & Bases• Conjugate Base

The species that remains after an acid has given up its proton

H3PO4 (aq) + H2O (l) ↔ H3O+ (aq) + H2PO4- (aq)

The stronger the acid, the weaker its conjugate base

AcidAcid Conjugate Conjugate BaseBase

• Conjugate Acid

The species that is formed when a base gains a proton

H3PO4 (aq) + H2O (l) ↔ H3O+ (aq) + H2PO4- (aq)

The stronger the base, the weaker its conjugate acid

Conjugate Acids & Bases

BaseBase Conjugate Conjugate AcidAcid

Proton-Transfer Reactions

• These reactions favor the production of the weaker acid and the weaker base.

Amphoteric Compounds

• Any species that can act as either an acid or a base

Ex: Water as a base:

H3PO4 (aq) + H2O (l) ↔ H3O+ (aq) + H2PO4- (aq)

Ex: Water as an acid:

NH3 (g) + H2O (l) ↔ NH4+ (aq) + OH- (aq)

Hydroxyl Group in Molecules• The –OH group in a molecule can be acidic or

amphoteric• As the number of oxygens that are bonded around the

atom with the –OH group increases, so does the acidity of the compound.

Oxygens pull Oxygens pull electron density electron density away from the away from the

hydrogen, hydrogen, making it appear making it appear

more positive more positive (and attractive (and attractive to water and to water and other bases)other bases)

Bases Neutralize Acids

Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl.

2 HCl + Mg(OH)2

MgCl2 + 2 H2O

Acids Neutralize Bases

HCl + NaOH NaCl + H2O

Neutralization reactions ALWAYS produce a salt and water.

Acids React with Carbonates

2HC2H3O2 + Na2CO3

2 NaC2H3O2 + H2O + CO2

Neutralization Reactions

• The reaction of hydromium and hydroxide ions to form water molecules

Steps:

1. Dissociation of a base in water

2. Acid donates a proton to water

3. Complete ionic equation

4. Net ionic equation (no spectator ions)

NeutralizationNeutralization

HCl + NaOH HCl + NaOH → NaCl + H→ NaCl + H22OO

Products of NeutralizationHCl + NaOH

H2SO4 + Ca(OH)2

HNO3 + KOH

The products of neutralization are always a ______ and _______.

NaCl + H2O

CaSO4 + 2 H2O

KNO3 + H2O

salt water

Acid Rain• Formation of Acid Rain:

Nonmetallic oxides enter the atmosphere as a result of burning coal, auto exhaust and other forms of air pollution.

Nonmetallic oxides in the air then combine with water to form oxyacids:

SO3 (g) + H2O (l) → H2SO4 (aq)

SOSO22, SO, SO33, CO, CO22, ,

NO, NONO, NO22

Effects of Acid Rain on Marble(calcium carbonate)

George Washington:BEFOREBEFORE

George Washington:AFTERAFTER

CaCOCaCO33 (s)(s) + 2H + 2H33OO++ (aq)(aq) → Ca→ Ca+2+2 (aq)(aq) + CO + CO22 (g)(g) + 3H + 3H22O O (l)(l)