Chapter 20: Acids and Bases

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Chapter 20 Acids and Bases
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Acids

• Give food a sour flavor
• Aqueous solutions of acids are electrolytes
• React with compounds containing hydroxide ions to
  form salt and water

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Bases

• Feel slippery
• Taste bitter
• Are electrolytes
• React with acids to form water and salt

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Formulas of Acids

• An acid produces hydrogen ions- generic acid HX
  (X is an ion)
• IE
• HCl
• H2SO4
• HNO3

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Naming Acids w/out Oxygen

• Start with hydro
• Name the ion
• Change ide to ic
• HCl Hydrochloric Acid
• HBr- Hydrobromic Acid
• HI- Hydroiodic Acid

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Acids that contain Polyatomic Ions

• Change ate to ic
• Change ite to ous
• H2SO4? Sulfate ? Sulfuric Acid
• H2SO3 ? Sulfite ? Sulfurous Acid

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Naming Bases

• Bases produce hydroxide ions when dissolved in
  water
• Name like any ionic compound
• NaOH- Sodium Hydroxide
• LiOH- Lithium Hydroxide

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Self Ionization of Water
Hydroxide Ion
Hydronium Ion
H2O H OH-
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Self Ionization of Water

• H2O H OH-
• Pure water at 25oC
• H 1.0x 10-7 M
• OH- 1.0 x 10-7 M
• H OH-
• neutral

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Le Chateliers Principle

• H2O H OH-
• As H increases OH- decreases
• As OH- increases H decreases

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Ion-Product Constant of Water (Kw)

• Kw H x OH- 1 x 10 -14 M2

H 1.0x 10-7 M OH- 1.0 x 10-7 M
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Acidic Solution
H2O

• HCl (g) H (aq) Cl- (aq)
• H gt OH-
• H gt 1 x 10-7 M

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Alkaline Solution (Basic)
H2O

• NaOH (s) Na (aq) OH- (aq)
• H lt OH-
• OH- gt 1 x 10-7 M
• H lt 1 x 10-7 M

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pH

• pH scale 0-14
• lt7 acidic
• gt7 basic
• 7 neutral

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pH

• pH -logH
• Acidic solution pHlt7 H gt 1X10-7 M
• Neutral solution pH7 H 1X10-7 M
• Basic Solution pHgt7 H lt 1X10-7 M

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pH

• H 1x 10-7 M
• pH - log1x 10-7 M
• pH 7
• Neutral
• H 1x 10-2 M
• pH - log1x 10-2 M
• pH 2
• Acidic

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pOH

• pOH -logOH-
• Acidic solution pOHgt7 OH- lt 1X10-7 M
• Neutral solution pOH7 OH- 1X10-7 M
• Basic Solution pOHlt7 OH- gt 1X10-7 M

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pOH

• pH pOH 14
• pH 14-pOH
• pOH 14-pH

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Acid-Base Indicators (In)

• An indicator is an acid or base that undergoes
  dissociation in a known pH range
• Acid form and base form have different colors
• HIn (aq) H (aq) In- (aq)
• Acid form Base form

OH-
H
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Limitations of Indicators

• pH values given at 25o C
• Indicators color may be distorted if the solution
  being tested is not colorless
• Dissolved salts affect indicators

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pH Meter
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Arrhenius Acids and Bases

• Acids are hydrogen containing compounds that
  ionize to yield H ions in an aqueous solution
• Bases are compounds that ionize to yield
  hydroxide ions in aqueous solution

Svante Arrhenius (1859-1927)
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Common Triprotic Acids

• H3PO4 Phosphoric Acid

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• Not all compounds that contain hydrogens are
  acids
• Only hydrogens in a very polar bond are ionizable

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BrØnsted-Lowry Acids and Bases

• Acid- A hydrogen ion donor
• Base- A hydrogen ion acceptor
• All of the acids and bases according to the
  Arrhenius definition are still acids and bases
• NH3 (aq) H2O (l) NH4 (aq) OH- (aq)

Ammonia (hydrogen ion acceptor)
Water (hydrogen ion donor)
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Conjugate Acid-Base Pair

• Conjugate acid the particle formed when a base
  gains a hydrogen ion
• Conjugate base the particle that remains when an
  acid has donated a hydrogen ion
• NH3 (aq) H2O (l) NH4 (aq) OH- (aq)

Acid
Conjugate Acid
Conjugate Base
Base
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Amphoteric

• A substance that can act as either an acid or a
  base
• water

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Lewis Acids and Bases

• A Lewis Acid can accept a pair of electrons to
  form a covalent bond
• A Lewis base can donate a pair of electrons to
  form a covalent bond

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Strong Acids

• Strong acids are completely ionized in an aqueous
  solution
• Hydrochloric Acid
• Sulfuric Acid
• HCl (g) H2O (l) H3O (aq) Cl- (aq)

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Weak Acids

• Weak acids ionize only slightly in aqueous
  solution, ionization is not complete
• CH3COOH (aq) H2O H3O(aq) CH3COO- (aq)
• Ethanoic Acid
  Ethonate ion
• 
  lt1

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Equilibrium Constant (Keq)

• CH3COOH (aq) H2O H3O(aq) CH3COO- (aq)
• Keq H3O x CH3COO-
• H2O x CH3COOH
• Keq gt1 products favored at equilibrium
• Keq lt 1 reactants favored at equilibrium

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Acid Dissociation Constant (Ka)

• CH3COOH (aq) H2O H3O(aq) CH3COO- (aq)
• Keq x H2O Ka H3O x CH3COO-
• CH3COOH
• The ratio of the dissociated (or ionized) form of
  an acid to the concentration of the undissociated
  (nonionized) form

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Acid Dissociation Constant (Ka)

• Reflects the fraction of an acid in ionized form
• Also called ionization constants
• Weak acids have a small Ka
• Strong acids have a big Ka

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Kas for Diprotic and Triprotic Acids

• Diprotic and triprotic acids lose their hydrogens
  one at a time
• Each ionization has its own ionization constant
• H3PO4 H H2PO4- Ka 7.5 x 10 -3
• H2PO4- H HPO42- Ka 6.2 x 10 -8
• HPO42- H PO43- Ka 4.8 x
  10 -13

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Dissociation of a strong acid
Hydrochloric Acid
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Strong Bases

• Strong bases dissociate completely into metal
  ions and hydroxide ions in aqueous solutions
• ALL bases containing OH- ions are strong bases

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Weak Bases

• Weak bases react with water to form the hydroxide
  ion and the conjugate acid of the base
• NH3 (aq) H2O (l) NH4 (aq) OH- (aq)
• lt1

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Base Dissociation Constant (Kb)

• NH3 (aq) H2O (l) NH4 (aq) OH- (aq)
• Keq x H2O Kb NH4 x OH-
• NH3

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Base Dissociation Constant (Kb)

• Indicates the ability of a weak base to compete
  with the very strong base OH-
• The smaller the Kb value the weaker the base
• Kb conjugate acid x OH-
• conjugate base

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Calculating Dissociation Constants (Ka)

• You must know
• The initial molar concentration of the acid
• The pH or H concentration of the solution

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Ice Tables
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Example

• For a solution of methanoic acid (HCOOH) exactly
  0.1 M, H 4.2 x 10-3 M. Calculate the Ka.
• HCOOH H2O H3O HCOO-
• Initial .1M 0M 0M
• Change 4.2 x 10-3 M

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Example
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Example

• Ka H3O x HCOO-
• HCOOH
• Ka 4.2 x10 -3 x 4.2 x10 -3
• 0.0985
• Ka 1.8 x 10 -4

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Neutralization Reactions

• When an aqueous acid and an aqueous base react to
  form salt and water

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Strong/Acids/Bases

• HCl (aq) NaOH (aq) ? H2O (l) NaCl (aq)
• H2SO4 (aq) 2KOH (aq) ? 2H2O (l) K2SO4 (aq)
• If solutions of strong acids/bases are mixed in
  the mole ratios specified by the balanced
  equations, neutral solutions will result

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Weak Acids/Bases

• Reactions of weak acids and bases do NOT usually
  for neutral solutions

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Titration

• The concentration of an acid (or base) in a
  solution can be determined by performing a
  neutralization reaction

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Steps for Titration

• A measured volume of an acidic solution is added
  to a flask

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Steps for Titration

• Several drops of the indicator are added to the
  solution

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Steps for Titration

• Measured volumes of a base of known concentration
  are mixed into the acid until the indicator
  barely changes color

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Standard Solution

• The solution of known concentration

Standard Solution
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End Point

• The point at which the indicator changes color

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Equivalence Point
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Equivalent

• Is the amount of acid (or base) that will give 1
  mole of hydrogen (or hydroxide) ions

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Equivalents

• Monoprotic Acids
• HCl ? H Cl-
• HNO3 ? H NO3-
• CH3COOH ? H CH3COO-

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Equivalents

• Diprotic Acids
• H2SO4 ? 2H SO42-
• Triprotic Acids
• H3PO4 ? 3H PO43-

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Equivalents

• Bases
• NaOH ? Na OH-
• Ca(OH)2 ? Ca 2 2OH-
• Al(OH)3 ? Al 3 3OH-

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Titration

• HCl (aq) NaOH (aq) ? H2O (l) NaCl (aq)
• 1 mol 1 mol 1 mol 1mol
• H2SO4 (aq) 2KOH (aq) ? 2H2O (l) K2SO4 (aq)
• 1 mol 2 mol 2 mol 1 mol

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Example

• How many milliliters of 0.45 M hydrochloric acid
  must be added to 25.0 mL of 1.00 M potassium
  hydroxide to make a neutral solution?

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Gram Equivalent Mass

• The mass of 1 equivalent of a substance
• HCl (1 Equivalent)
• H 1
• Cl 35.5
• Gram Equivalent Mass 36.5

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Gram Equivalent Mass

• H2SO4 (2 Equivalents)
• H 1x2
• S32
• 016 X 4
• Gram Equivalent Mass 98g / 2 49 g

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Normality (N)

• Concentration expressed as the number of
  equivalents of solute in 1 liter of solution

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Dilutions

• M1V1 M2V2

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Salt Hydrolysis

• A salt consists of an anion from an acid and a
  cation from a base
• CH3COOH NaOH ? CH3COONa H2O
• Acetic Acid Sodium
• Hydroxide
• Weak Acid Strong Base pH 8.7

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Salt Hydrolysis

• In salt hydrolysis, the cations or anions of the
  dissociated salt remove or donate hydrogen ions
  to water.

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Salt Hydrolysis

• Solutions containing hydrolizing salts may be
  acidic or basic

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Salt Hydrolysis

• Hydrolizing salts are usually derived from a
  strong acid and a weak base, or, a strong base
  and a weak acid

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Salt Hydrolysis

• CH3COOH NaOH ? CH3COONa H2O
• CH3COONa ? CH3COO- Na
• CH3COO- H2O CH3COOH OH-
• H acceptor H Donor
• Bronsted-Lowry Bronsted-Lowry
• Acid Base

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Salt Hydrolysis

• Strong Acid Strong Base ? Neutral
• Strong Acid Weak Base ? Acidic
• Weak Acid Strong Base ? Basic

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Buffers

• Solutions in which the pH remains relatively
  constant when small amounts of acid or base are
  added

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Buffers

• CH3COONa ? CH3COO- Na
• CH3COO- H CH3COOH
• When acid is added, CH3COO- absorbs them so the
  pH does not change noticeably

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Buffers

• CH3COOH OH- CH3COO- H2O
• When a base is added to the solution, CH3COOH
  donates hydrogen ions to form water and CH3COO-
  and the pH does not change drastically

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Buffer Capacity

• The amount of acid or base that can be added to a
  buffer before a significant change in pH occurs

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The Solubility Product Constant (Ksp)
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The Solubility Product Constant (Ksp)

• AgCl (s) Ag (aq) Cl- (aq)
• Keq AgCl-
• AgCl
• Keq x AgCl AgCl- Ksp

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Common Ion Effect

• A common ion is an ion that is common to both
  salts
• PbCrO4 (s) Pb 2 (aq) CrO42- (aq)
• Adding Pb(NO3)2 would shift the equilibrium
• Pb 2 is a common ion

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Common Ion Effect

• The common ion effect is the lowering of
  solubility of a substance by the addition of a
  common ion

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Example

• What is the concentration of sulfide ion in a 1.0
  L solution of iron (II) sulfide to which 0.04 mol
  of iron (II) nitrate has been added? The Ksp of
  FeS is 8x10-19.

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The Solubility Product Constant (Ksp)

• The Ksp can be used to predict whether a
  precipitate will form when solutions are mixed
• If the ion product concentration is greater than
  the Ksp of the compound formed from the 2 ions, a
  precipitate will form

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Example

• Predict whether calcium carbonate will
  precipitate when 0.5 L of 0.001 M Ca(NO3)2 is
  mixed with 0.5 L of 0.0008 M Na2CO3 to form 1 L
  of solution. The Ksp of CaCO3 is 4.5x 10-9