Chapter 7 Acids and Bases:

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Chapter 7 Acids and Bases

• Outline
• 1. Introduction
• 2. Arrhenius theory
• 3. Bronsted-Lowry theory
• 4. Reactions of acids and bases
• 5. pH scale
• 6. Applications of acids and bases

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1. Introduction
Importance of chemistry of acids and bases

• Acids and based are very common chemicals

Many chemical transformation involves acid-base
reactions.
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Common properties of acids

• Tastes sour
• DO NOT TASTE UNKNOWN CHEMICALS
• Causes litmus indicator dye to turn red
• Dissolves active metals to produce H2
• Reacts with bases to produce water and salt

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Common properties of bases

• Tastes bitter
• DO NOT TASTE UNKNOWN CHEMICALS
• Feels slippery on skin
• Causes litmus indicator dye to turn blue
• Reacts with acids to form water and salt

Why do acids and base have such properties?
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2. Arrhenius Theory of Acids

• Acid substance that breaks up in aqueous
  solution into H and anions
• H hydrogen ions or protons
• Example nitric acid ionize in water.
• HNO3(aq) ? H(aq) NO3(aq)
• It is the H that gives properties of acids
• Tastes sour
• Causes litmus indicator dye to turn red
• Dissolves active metals to produce H2
• Reacts with bases to produce water and salt

Svante Arrhenius (18591927)
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Arrhenius Theory of Bases

• Base a substance that produces hydroxide ions
  (OH ) in aqueous solution
• OH hydroxide
• Example NaOH(aq) ? Na(aq) OH(aq)
• It is the OH that gives the properties of bases.
• Tastes bitter
• Feels slippery on skin
• Causes litmus indicator dye to turn blue
• Reacts with acids to form water and salt

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Arrhenius Theory, Continued
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Arrhenius AcidBase Reactions

• The H from the acid combines with the OH- from
  the base to make a molecule of H2O.
• It is often helpful to think of H2O as HOH.
• The cation from the base combines with the anion
  from the acid to make a salt.
• acid base ? salt water
• HCl(aq) NaOH(aq) ? NaCl(aq) H2O(l)

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Limitations of Arrhenius Theory

• - H ions do not exist in water solution.
  Protons react with water to form hydronium ion,
  (H3O)
• H H2O ? H3O
• The Arrhenius Theory does not explain the
  basicity of ammonia and similar compounds.
• It only applies to reactions in aqueous solution.

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3. Brønsted-Lowry Theory

• Acid proton donor, e.g. HCl
• HCl H2O ? H3O Cl-
• Base proton acceptor, e.g. NH3
• NH3 H2O ? NH4 OH-

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Arrhenius Theory vs BrønstedLowry Theory

• BrønstedLowry theory
• HCl(aq) H2O(l) ?
• Cl-(aq) H3O(aq)
• HF(aq) H2O(l) ?
• F-(aq) H3O(aq)
• NaOH(aq) ?
• Na(aq) OH-(aq)

• Arrhenius theory
• HCl(aq) ?
• H(aq) Cl-(aq)
• HF(aq) ? H(aq) F-(aq)
• NaOH(aq) ?
• Na(aq) OH-(aq)

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Concept of conjugated acids and bases
Conjugate acids and bases When an acid donates a
proton, it becomes its conjugate base when a
base gains a proton, it becomes its conjugate
acid. e.g.

• HCl NH3 ? NH4 Cl-
• Acid Base conjugate conjugate
• acid of NH3 base of HCl
• H2O CN- ? HCN OH-
• Acid Base conjugate conjugate
• acid of CN- base of H2O

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Conjugate Pairs
In the reaction H2O NH3 ? HO NH4
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Exercise 1. Identify the BrønstedLowry Acids and
Bases and their conjugates in the following
reaction.
H2SO4 H2O ? HSO4 H3O
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Exercise 2. Identify the BrønstedLowry Acids and
Bases and their conjugates in the following
reaction.
HCO3 H2O ? H2CO3 HO
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Exercise 3. Write the Formula for the conjugate
acid of the following
H2O NH3 CO32- H2PO4-
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Exercise 4. Write the Equations for the Following
Reacting with Water and Acting as a Monoprotic
Acid. Label the Conjugate Acid and Base.

• HBr
• HSO4-

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Typical examples of Bronsted acids

• a) Non-metal hydride compounds, have acid
  hydrogens attached to a nonmetal atom e.g.
• HF, H2S, H2Te
• b) Carboxylic acids, have COOH group. e.g.
• CH3COOH,
• Only one of the H is acidic.
• The H is on the COOH

HBr H2O Br- H3O
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c) Hydroxoacids, in which the acidic proton is on
a hydroxyl group without a neighboring oxo group
( O), e.g.

• d) Oxoacids, in which the acidic proton is on a
  hydroxyl group with a oxo group (O) attached to
  the same atom, e.g.

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Typical examples of Bronsted bases

• Most ionic bases contain OH ions.
• NaOH, Ca(OH)2
• Some contain CO32- ions.
• CaCO3 NaHCO3
• Molecular bases contain structures that react
  with H.
• Mostly amine groups, e.g. NH3, CH3NH2

Caffeine
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Acid and base can also be generated from
Reactions of oxide with water

• Nonmetal oxides react with water to give
  acid.e.g.
• SO3 H2O ? H2SO4

Metal oxides react with water to form base.
e.g. CaO H2O ? Ca(OH)2
Anhydride means without water. Nonmetal oxides
are called acidic anhydrides. Metal oxides are
called base anhydrides.
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Exercise. Give the formula for the acid formed
when sulfur dioxide reacts with water.
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Common Acids
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Common Bases
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Strong and Weak Acids

• Strong acid acid completely reacts with water or
  completely ionizes in water
• HCl H2O ? H3O Cl-
• or HCl(aq) ? H(aq) Cl-(aq)
• Strong acids donate practically all their Hs.
• 100 ionized in water.
• Strong electrolyte.
• H3O strong acid.

Concentration of H3O
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Examples of Strong Acids
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Weak Acids

• Weak acid acid reacts only slightly with water
  or partially ionizes in water. e.g.
• HF H2O ? H3O F-
• or HF(aq) ? H(aq) F-(aq)

• Weak acids donate a small fraction of their Hs.
• Most of the weak acid molecules do not donate H
  to water.
• Much less than 1 ionized in water.
• H3O ltlt weak acid.

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Examples of Weak Acids
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Strong and Weak Bases

• Strong base base completely ionizes in water.
  e.g.
• NaOH(aq) ? Na(aq) OH-(aq)

• HO strong base x ( OH).

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Examples of Strong Bases
Common strong bases most Group 1A and 2A
hydroxides
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Weak bases

• Weak base only slightly ionizes in water
• NH3(aq) H2O ? NH4(aq) OH-(aq)

• In weak bases, only a small fraction of molecules
  accept Hs.
• Most of the weak base molecules do not take H
  from water.
• Much less than 1 ionization in water.
• HO ltlt strong base.

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Examples of Weak Bases
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Relationship Between Strengths of Acids and Their
Conjugate Bases

• The stronger an acid is, the weaker the
  attraction of the ionizable H for the rest of the
  molecule is.
• The better the acid is at donating H, the worse
  its conjugate base will be at accepting an H.
• Strong acid HCl H2O ? Cl H3O Weak
  conjugate base
• Weak acid HF H2O ? F H3O Strong
  conjugate base

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Amphiprotic

• A substance that can either donate or accept a
  proton. e.g.
• H2O is a common amphiprotic substance
• Reacts with base H2O NH3 ? NH4 OH
• Reacts with acid H2O HCl ? Cl H3O

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4. Reactions of acids and base

• Neutralization Reaction of an acid and a base.
• Acid base ? water salt

During neutralization, an acid reacts with a
base, forming water and a salt.
Salt cation from base anion from acid.
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Exercise 1. Write the Equation for the Reaction
of Aqueous Nitric Acid with Aqueous Calcium
Hydroxide.

• 1. Write the formulas of the reactants.

• 2. Write the formulas of the products.
• 3. Balance the equation.
• May be quickly balanced by matching the numbers
  of H and OH to make H2O.
• Coefficient of the salt is always 1.

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Exercise 2. Complete Each Reaction.

• Ca(OH)2(s) H2SO3(aq) ?
• HClO3(aq) Pb(OH)4(s) ?
• CaCO3(s) HNO3(aq) ?
• Mg(HCO3)2(aq) HC2H3O2(aq) ?

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Acid Reactions Acids React with Metals

• Acids react with many metals.
• But not all!!
• When acids react with metals, they produce a salt
  and hydrogen gas. e.g.

Acid metal ? H2 (g) salt
3 H2SO4(aq) 2 Al(s) ? Al2(SO4)3(aq) 3 H2(g)
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Exercise. Write an Equation for the Reaction of
Hydroiodic Acid with Na Metal.

• Write formulas of reactants.
• Identify the type of reaction and predict the
  pattern.
• Determine the charge on the cation, and the
  formula of the salt.

• Write the skeletal equation.
• Balance the equation.

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Acid Reactions Reactions of acid with metal
oxide.
Acid metal oxide ? salt H2O(l)
Exercise. Write an Equation for the Reaction of
Hydrobromic Acid with Sodium Oxide.

• 1. Write formulas of reactants.
• 2. Identify the type of reaction and predict the
  pattern.
• Determine the charge on the cation, and the
  formula of the salt.

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Exercise. Write an Equation for the Reaction of
Hydrobromic Acid with Sodium Oxide(s), continued

• 4. Write the skeletal equation.
• 5. Balance the equation.

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Exercise. Complete and Balance the Following
Reactions

• HCl(aq) CaO(s) ?
• HCl(aq) Ca(s) ?

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Exercise. Complete and Balance the Following
Reactions, Continued

• 2 HCl(aq) CaO(s) ? CaCl2(aq) H2O(l)
• 2 HCl(aq) Ca(s) ? CaCl2(aq) H2(g)

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Acid Reactions Reactions of strong acid with
salt.
strong acid salt ? weak acid new salt

• CaCO3(s) 2 HNO3(aq) ? Ca(NO3)2(aq) H2CO3
  (aq)

H2CO3 decomposes into CO2(g) H2O(l)
H2CO3 ? CO2(g) H2O(l)
CaCO3(s) 2 HNO3(aq) ? Ca(NO3)2(aq) CO2(g)
H2O (l)
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5. pH scale

• pH is a means of expressing the acidity and
  basicity of a solution.
• It is related to the concentration of H.
• pH log H (negative logarithm)

pH means power of hydrogen.
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pH Scale Describing Acidity

• Typical values range from 0 to 14
• pH 7 neutral
• pH gt 7 basic
• pH lt 7 acidic

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pH in Common Solutions
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The Hydrangea macrophylla blossoms in pink or
blue, depending on soil pH. In acid soils the
flowers will be blue, in alkaline soils the
flowers will be pink.
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Practice pH Problems
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Exercise. Determine the H3O for Each of the
Following

• pH 2.7
• pH 12
• pH 0.60

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Acid/base are important industrial
chemicalsMany top industrial chemicals are
acids or bases.
6. Applications of Acid/base
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Uses of Common Acids
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Uses of Common Bases
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Acids in Industry

• H2SO4
• Leading chemical product in U.S.
• Used to make fertilizers
• Found in car batteries
• HCl
• Muriatic acid
• Removes rust from metal
• Removes lime from fixtures

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Bases in Industry

• NaOH
• Found in household cleaners,
• Used to make soaps
• CaO
• Lime
• Used to make mortar and cement

• NH3
• fertilizer

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Acids, Bases and and Health

• Stomach acid, HCl
• Aids digestion
• Blood maintains narrow pH range (approximately
  7.40, normal range is 7.35 7.45).
• Required for normal functioning of body
• Concentrated acids and bases are corrosive poisons

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Stomach Acid and Antacids

• Stomach excretes HCl
• Aids digestion of food
• Too much HCl ? Hyperacidity
• Caused by emotional stress or overindulgence
• To remove excess acid, one use an antacid,
  usually a base, to neutraulize the acid.

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Antacids and bases

• May contain one of the following bases
• NaHCO3
• Baking soda
• Safe and effective
• Not recommended for people with high blood
  pressure
• CaCO3
• Effective
• Should not be used for long periods of time

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• 3. Al(OH)3
• Similar behavior to CaCO3
• Mg(OH)2
• milk of magnesia
• Some brands of antacids are combinations of the
  above chemicals