Acids and Bases

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Chapter 19

• Acids and Bases

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Questions for Today

1. What are the physical and chemical property of
   Acids and Bases?
2. How do you classify solutions as acidic, basic,
   or neutral?
3. Compare and Contrast Arrhenius and Bronsted-Lowry
   Models of acids and bases.
4. What is a conjugate acid or base and how do you
   identify it?

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Class question

• Where can acids be found?
• Sodas
• Stomach
• Vinegar
• Citrus fruits

• Where can bases be found?
• Soap
• Drano
• Antacid tablets
• Windex
• detergent

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Properties of Acids and Bases

• Acids and bases are some of the most important
  industrial compounds on Earth.
• We use 30 40 billion kg of sulfuric acid each
  year to make many common products.
• Acids and Bases can be identified using their
  chemical and physical property?
• What are examples of chemical or physical
  properties?

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Properties of Acids and Bases

• Acids
• Taste sour
• Feel like water
• Reacts with Metals
• Effervesence
• Corrosive
• Turns litmus paper red

• Bases
• Taste Bitter
• Feels Slippery
• Does not react with Metals
• Reacts with Organic Tissue
• Caustic Burns
• Turns litmus paper blue

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Strength of Acids Bases

• Strong Acid/Base
• 100 ionized in water, comes apart completely in
  water
• Strong electrolyte, conducts electricity
• Strong Acids HCl, HNO3, H2SO4
• Strong Bases NaOH, KOH

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Strength of Acids Bases

• Weak Acid/Base
• Does not ionize completely, does not come apart
  completely in water
• Weak electrolyte, does not conduct electricity
  well.
• Weak Acids HF, CH3COOH
• Weak Base NH3

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Warning

• Never use taste in a lab setting to identify
  acids or bases unless told to by your science
  teacher.

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Acid/Base Indicators

• An acid-base indicator is a weak acid or a weak
  base.
• An Indicator changes color over a range of
  hydrogen ion concentrations. This range is
  expressed as a pH range.
• Some common indicators are litmus paper, cabbage
  juice, phenolphthalein bromthymol blue etc.

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Identifying and Classifying Acids and Bases

• Litmus Paper
• A chemically treated paper used to identify
  acids/bases by color comparision.
• Litmus Paper turns redder in the presence of an
  Acid while, in a base, the paper becomes blue.
• Electrolytic
• An electrolyte is any solution that contains ions
  and can conduct electricity.
• Both acids and bases can conduct electricity
• Pure Water is a nonconductor of electricity.

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Identifying and Classifying Acids and Bases

• Why are some aqueous solutions acids, bases, or
  neutral?
• The amount of Hydrogen ions (H) or Hydroxide
  ions (OH-) determines the acidity or basidity of
  a solution.
• An Acidic solution contains more H ions than OH-
  ions
• A Basic Solution contains more OH- ions than H
  ions.
• Neutral Solutions contain equal amounts of H
  ions and OH- ions.

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Who Discovered Acids?

• First chemist to define acids and bases was
  Swedish chemist, Svante Arrhenius.
• The Arrhenius Model states that an acid is a
  substance that contains hydrogen and ionizes to
  produce Hydrogen ions (H) in aqueous solution
  while a Base is a substance that contains a
  Hydroxide group and dissociates to produce a
  hydroxide ion (OH-) in aqueous solution.

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Example of Arrhenius Model

• HCl ? H Cl-
• Hydrochloric Acid will dissociate into Hydrogen
  ions and Chlorine ions when dissolved in Water.
• NaOH ? Na OH-
• When the ionic compound NaOH dissolves in water,
  it dissociates to produce Hydroxide ions, which
  makes the solution Basic.

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Flaw with Arrhenius model

• Not all bases contain hydroxide
• Ex ammonia (NH3) is basic
• Therefore a new type of acid/base must be
  determined

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Bronsted-Lowry Model

• Bronsted-Lowry Acid
• Defn proton/H donor
• can give H to another species
• Bronsted-Lowry Base
• Defn proton/H acceptor
• can take H from another species

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Bronsted-Lowry Model

• REMEMBER!!!! REMEMBER!!!!
• Acids Donate, Bases Accept protons
• Ashley donates Blood Always

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Bronsted-Lowry Model

• Examples
• HCl H2O ? Cl- H3O

What is happening here?
Acid (donates proton)
Base (accepts proton)
Which is the acid? base?
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Bronsted-Lowry Model

• Examples
• NH3 H2O ? NH4 OH-

What is happening here?
Acid (donates proton)
Base (accepts proton)
Which is the acid? base?
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Amphoteric

• Defn substance that can act as both acids and
  bases
• HNO3 H2O ? H3O NO3-
• NH3 H2O ? NH4 OH-

Is H2O a base or acid?
base
Is H2O a base or acid?
acid
Water is amphoteric b/c it is acts as a base in
one reaction and acts as an acid in the second
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Neutralization Reactions

• Strong acid Strong base ? Salt Water
• Ex. HCl(aq) NaOH(aq) ? NaCl(aq) H2O

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pH

• Acids Bases

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The pH Scale

• The pH scale indicates the hydronium ion
  concentration, H3O
• In other words how many H3O ions are in a
  solution. If there are a lot we assume it is an
  acid, if there are very few it is a base.

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The pH Scale

0
14
7
INCREASING ACIDITY
INCREASING BASICITY
NEUTRAL
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The pH Scale

• pH of Common Substances

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Learning Check AB1

• Describe the solution in each of the following
  as 1) acid 2) base or 3)neutral.
• A. ___soda
• B. ___soap
• C. ___coffee
• D. ___ wine
• E. ___ water
• F. ___ grapefruit

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Solution AB1

• Describe each solution as
• 1) acid 2) base or 3) neutral.
• A. _1_ soda
• B. _2_ soap
• C. _1_ coffee
• D. _1_ wine
• E. _3_ water
• F. _1_ grapefruit

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Learning Check AB2

• Identify each as characteristic of an A) acid
  or B) base
• ____ 1. Sour taste
• ____ 2. Produces OH- in aqueous solutions
• ____ 3. Chalky taste
• ____ 4. Is an electrolyte
• ____ 5. Produces H in aqueous solutions

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Solution AB2

• Identify each as a characteristic of an A) acid
  or B) base
• _A_ 1. Sour taste
• _B_ 2. Produces OH- in aqueous solutions
• _B_ 3. Chalky taste
• A, B 4. Is an electrolyte
• _A_ 5. Produces H in aqueous solutions