Transcript Chapter 15 Acids & Bases

Chapter 14
Acids & Bases
14.1 Properties of Acids and Bases
Properties of Acids
1. 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 Acids
5. 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 moreelectronegative 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 Acid
Highest 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 Acid
o A flavoring agent in sodas
o Used in the manufacture of
detergents & fertilizers
o Not a common laboratory reagent
Some Common Industrial Acids
• Acetic Acid
Concentrated “glacial” acetic
acid used in the manufacture of
plastics
Used in making pharmaceuticals
Acetic acid is the acid present in
vinegar
Properties of Bases
1. Aqueous solutions of bases have a bitter
taste
2. Bases change the color of acid-base
indicators
Turns red litmus blue
Turns phenolphthalein magenta/purple
3. 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+, acceptors
7. Have a pH value of greater than 7
8. Neutralize acids
Arrhenius Acids & Bases
• Arrhenius Acid
A chemical compound that increases
the concentration of hydrogen ions,
H+, in aqueous solution
• Arrhenius Base
A substance that increases the
concentration of hydroxide ions, OH-,
Swedish Chemist
in aqueous solution
Aqueous Solutions of Acids
• Acids are molecular compounds that
ionize in solution
HNO3 + H2O → H3O+ + NO3Proton
Donor
Proton
Acceptor
H2SO4 + H2O → H3O+ + HSO4-
H2O + HCl → H3O+ + Cl-
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 Acids
Organic 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 14
Acids & 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:
• Diprotic Acid:
HC2H3O2
HCl
H2SO4
Polyprotic Acids
• Triprotic Acids:
Can
donate 1
H
Can
donate 2
Hs
Can
donate 3
Hs
H 3C 6H 5O 7
H3PO4
• * Each successive proton is harder to remove!
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 14
Acids & 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)
Acid
Conjugate
Base
The stronger the acid, the weaker its conjugate base
Conjugate Acids & Bases
• Conjugate Acid
The species that is formed when a base gains a
proton
H3PO4 (aq) + H2O (l) ↔ H3O+ (aq) + H2PO4- (aq)
Base
Conjugate
Acid
The stronger the base, the weaker its conjugate acid
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
electron density
away from the
hydrogen,
making it
appear more
positive (and
attractive to
water and 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)
Neutralization
HCl + NaOH → NaCl + H2O
Products of Neutralization
HCl + NaOH 
NaCl + H2O
H2SO4 + Ca(OH)2 
HNO3 + KOH 
CaSO4 + 2 H2O
KNO3 + H2O
The products of neutralization are always a
salt and _______.
water
______
Acid Rain
SO2, SO3, CO2,
NO, NO2
• 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)
Effects of Acid Rain on Marble
(calcium carbonate)
George Washington:
BEFORE
George Washington:
AFTER
CaCO3 (s) + 2H3O+ (aq) → Ca+2 (aq) + CO2 (g) + 3H2O (l)