Chapter 4: Types of Chemical Reactions

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Chapter 4 Types of Chemical Reactions

• Goals
• To be able to predict chemical reactivity.
• To know how to synthesize specific compounds.

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Types of Reactions

• Acid-Base proton-transfer
• Oxidation-Reduction electron-transfer
• Precipitation formation of insoluble salts
• Gas Forming
• Organic
• Substitution
• Addition
• Elimination

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Reactions in Aqueous Solution

• Unless mentioned, all reactions studied this and
  next week occur in aqueous solution.

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Electrolytes
Strong Electrolytes solute breaks apart to give
ions in solution. NaCl ? Na Cl- Weak
Electrolytes solute partially breaks apart to
give ions. CH3CO2H ? CH3CO2- H
happens less than 5 Nonelectrolytes no ions
formed. CH3CH2OH
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Brønsted-Lowery Acid-Base Definitions

• An acid is a substance that donates a proton (H)
  to a base
• A base is a substance that accepts a proton (H)
  from an acid

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Brønsted-Lowery Definitions

• acid donates a proton (H) to a base
• base accepts a proton (H) from an acid
• Acid-base reactions can be reversiblereactants
  ? products or products ? reactants

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Brønsted-Lowery Definitions

• An acid is a substance that donates a proton (H)
  to a base
• A base is a substance that accepts a proton (H)
  from an acid
• Acid-base reactions can be reversiblereactants
  ? products or products ? reactants

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Important Acids and Bases
Strong Acids HCl hydrochloric HBr hydrobromic H
I hydroiodic HNO3 nitric H2SO4 sulfuric HClO4
perchloric Weak Acid CH3CO2H acetic Any other
acids are WEAK
Strong Bases LiOH lithium hydroxide NaOH sodium
hydroxide KOH potassium hydroxide Ca(OH)2 c
alcium hydroxide Ba(OH)2 barium hydroxide Weak
Base NH3 ammonia
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• STRONG acids in water 100 of acid molecules
  form ions
• HCl(aq) H2O(l) ? H3O(aq) Cl-(aq)

H3O is hydronium ion
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• WEAK acids in water, 5 or less of acid
  molecules form ions (acetic, H3PO4, H2CO3)

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Polyprotic Acidsmultiple acidic H atoms

• H2SO4 ? H HSO4-
• HSO4- ? H SO42-
• Not all Hs are acidic
• CH3CO2H

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If H3PO4 reacts as an acid, which of the
following can it not make?

• 1. H4PO4
• 2. H2PO4-
• 3. HPO42-
• 4. PO43-

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If C2O42- reacts in an acid-base reaction, which
of the following can it not make?

• 1. H2C2O4
• 2. HC2O4-
• 3. 2 CO2

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Acid-Base Reactions

• Strong Acid Strong Base
• HCl(aq) NaOH(aq) ? NaCl(aq) H2O(l) acid
  base salt water

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Acid-Base Reactions

• Diprotic Acids or Bases
• H2SO4(aq) NaOH(aq) ?
• H2SO4(aq) Ba(OH)2(aq) ?
• HCl(aq) Ba(OH)2(aq) ?

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Acid-Base Reactions

• Strong Acid Weak Base
• HCl(aq) NH3(aq) ? NH4Cl(aq)

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Acid-Base Reactions

• Weak Acid Strong Base
• HCN(aq) NaOH(aq) ? NaCN(aq) H2O(l) acid
  base salt
  water

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Net Ionic Equations

• HCl(aq) NaOH(aq) ? NaCl(aq) H2O(l)
• What really happens
• H(aq) OH-(aq) ? H2O(l)
• Sodium ion and chloride ion are spectator ions

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Reactions involving weak bases

• HCl(aq) NH3(aq) ? NH4(aq) Cl-(aq)
• Net-Ionic Equation
• NH3(aq) H(aq) ? NH4(aq)

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CH3CO2H(aq) NaOH(aq) ?

• 1. CH3CO2H2(aq) NaO(aq)
• 2. CH3CO2-(aq) H2O(l) Na(aq)
• 3. CH4(g) CO2(g) H2O(l)

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HCN(aq) NH3(aq) ?

• 1. NH4(aq) CN-(aq)
• 2. H2CN(aq) NH2-(aq)
• 3. C2N2(s) 3 H2(g)

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Solution Concentration Molarity

• Molarity moles solute per liter of solution
• 0.30 mol NH3 dissolved in 0.500 LConcentration
  
• Written like NH3 0.60 M

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pH Scale

• In pure water, a few molecules ionize to form
  H3O and OHH2O H2O ? OH H3O
• In acidic and basic solutions, these
  concentrations are not equalacidic H3O gt
  OHbasic OH gt H3Oneutral H3O
  OH

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pH Scale

• Measure how much H3O is in a solution using pH
• pH lt 7.0 acidic
• pH gt 7.0 basic
• pH 7.0 neutral
• Measure of H3O and OH concentration (moles per
  liter) in a solution
• As acidity increases, pH decreases

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pH Scale

• The pH scale is logarithmic100 102 log(102)
  210 101 log(101) 11 100 log(100)
  00.1 101 log(101) 10.01 102 log(102)
  2
• pH log H3O
• pH if H3O 105? 109? Acidic or basic?
• pH if H3O 0.000057 M?

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Finding H3O from pH

• H3O 10-pH
• What is H3O if pH 8.9?

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pH Quantitative Measure of Acidity

• Acidity is related to concentration of H (or
  H3O)
• pH -logH3O