Acids and Bases

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Chapter 14

• Acids and Bases

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Lemons contain citric acid,

• Citric acid produces H ions in your mouth
• H ions react with protein molecules on your
  tongue
• The protein molecule changes shape sending an
  electrical signal to your brain Sour!

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Acids

• How do I identify an acid?
• HCl, H2SO4, HNO3
• First atom is hydrogen
• Produces H ions in water
• HCl(aq) ? H(aq) Cl-(aq)
• HCl H2O ? H3O(aq) Cl-(aq)
• H2SO4(aq) ?
• HNO3(aq) ?

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Acids and Bases

• ACIDS
• Taste sour
• Dissolve many metals
• Turn litmus paper red

• BASES
• Taste bitter
• Feel slippery
• Turn litmus paper blue

Sodium hydroxide or lye
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Arrhenius Theory

• Acids ionize in water to H ions and anions
• HCl(aq) ?
• Bases ionize in water to OH- ions and cations
• NaOH(aq) ?
• Neutralization reaction net ionic equation

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Brønsted-Lowery Theory

• Acid is H donor
• HCl(aq) ? H(aq) Cl-(aq)
• Base is H acceptor
• NH3(aq) H(aq) ? NH4(aq)
• H2O(l) H(aq) ? H3O(aq)
• What else do NH3 and H2O has in common?
• In the reaction, a H from the acid molecule is
  transferred to the base molecule

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Conjugate Acids and Bases
Conjugate Base
Acid

• NH3(aq) H2O(l) ? NH4(aq) OH-(aq)
• H2SO4(aq) H2O(l) ? HSO4-(aq) H3O(aq)
• C5H5N(aq) H2O(l) ? C5H5NH(aq) OH-(aq)

Base
Conjugate Acid
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Strong versus Weak Acids

• Strong acids completely dissociate into ions
• Major species ions
• Minor species un-ionized acid
• Weak acids slightly dissociate into ions.
• Major species un-ionized acid
• Minor species ions

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Strong versus Weak Acids
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Strong versus Weak Acids

• Which solution contains the strong acid?

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Strong versus Weak Acids
Strong Acids Weak Acids
HX(aq) ? H(aq) X-(aq) HX(aq) H(aq) X-(aq)
Nitric acid (HNO3) Most organic acids (acetic, oxalic, citric, fatty acids)
Sulfuric acid (H2SO4) Hydrofluoric acid (HF)
Hydrochloric acid (HCl) Carbonic acid - soda pop (H2CO3)
Hydrobromic acid (HBr) Hydroiodic acid (HI) Phosphoric acid - in Coke (H3PO4)
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Which Hydrogen atoms are acidic?
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Strong versus Weak Bases

• Strong bases completely dissociate into ions
• Major species ions
• Minor species un-ionized acid
• NaOH(aq) ? Na(aq) OH-(aq)
• Weak bases slightly dissociate, producing
  hydroxide ions.
• Major species un-ionized acid
• Minor species ions
• NH3(aq) H2O(aq) ? NH4(aq) OH-(aq)

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Strong versus Weak Bases
Strong Bases Weak Bases
MOH(aq) ? M(aq) OH-(aq) B(aq) H2O(l) BH(aq) OH-(aq)
Sodium hydroxide (NaOH) Ammonia, NH3
Potassium hydroxide (KOH) Lithium hydroxide (LiOH) Bicarbonate, HCO3-
Calcium hydroxide (Ca(OH)2) Strontium hydroxide (Sr(OH)2) Amines (Carbon group-NH2)
Barium hydroxide (Ba(OH)2) Water (H2O)
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Relative Strength of Conjugate Acids and Bases
Conjugate Base
Acid

• H2SO4(aq) H2O(l) ? HSO4-(aq) H3O(aq)
• A strong acid has a weak conjugate base
• A strong base has a weak conjugate acid
• A weak base has a strong conjugate acid
• A weak acid has a strong conjugate base

Base
Conjugate Acid
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Recognizing Acids and Bases

• Bases need a lone pair of electrons to accept a
  proton
• Acids leave behind stable anions

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Reactions of Acids and Bases

• Neutralization Reactions
• H2SO4(aq) Ca(OH)2(aq) ?
• Single Replacement Redox
• 3 H2SO4(aq) 2 Al(s) ?
• Acids react with metal oxides
• 3 H2SO4 Al2O3 ?

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Water

• NH3(aq) H2O(l) ? NH4(aq) OH-(aq)
• H2SO4(aq) H2O(l) ? HSO4-(aq) H3O(aq)
• Can act as an acid or base - amphoteric

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Water

• Auto-ionization
• H2O(l) H2O(l) ? H3O(aq) OH-(aq)
• At equilibrium, the H3O and OH- are constant
  and equal.
• KW H3OOH-1x10-14 at 25C
• What is the concentration of H3O at
  equilibrium?

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Acidic versus Basic Solutions

• Every aqueous solution contains water molecules,
  hydronium ions (H30 or H) and hydroxide ions
  (OH-)
• A neutral solution
• H OH-
• An acidic solution
• H gt OH-
• A basic solution
• OH- gt H

H2O
H2O
H
OH-
H2O
H2O
H2O
H
H2O
H
OH-
H2O
H
H2O
H2O
OH-
H2O
H
OH-
H2O
OH-
H2O
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pH scale

• Neutral pH 7
• Acidic pH lt 7
• Basic pH gt 7
• pH - log H3O
• Significant figures
• H3O 1.0 x 10-3
• pH 3.00

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Measuring pH
pH meter
Universal Indicators
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pH and pOH

• pOH - log OH-
• KW H3OOH- 1 x 10-14
• pH pOH 14
• Calculate the pH of a solution with
• H3O 1.0 x 10-8 M
• pOH 8.00
• OH- 1.0 x 10-8 M
• Calculate the H3O of a solution with
• pH 4.00
• pOH 6.00
• OH- 1.0 x 10-4 M
• Calculate the pH of 0.10 M HNO3 solution.

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pH and pOH

• pOH - log OH-
• KW H3OOH- 1 x 10-14
• pH pOH 14
• Calculate the pH of a solution with
• H3O 9.5 x 10-9 M
• pOH 4.80
• OH- 1.3 x 10-2 M
• Calculate the H3O of a solution with
• pH 4.80
• pOH 5.67
• OH- 7.2 x 10-11 M
• Calculate the pH of 0.10 M H2SO4 solution.
• Calculate the pH of 0.10 M Ba(OH)2 solution.

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Titrations
Add NaOH (with indicator)
Basic solution
Oxalic acid solution

• To a colorless acidic solution, we will add
  base.
• When the solution is basic, it will be red.
• We are looking for the equivalence point where
  the
• moles of H moles of OH-
• We will determination of molarity of NaOH
  solution

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Calculations
H2C2O4 NaOH H2O Na2C2O4
0.628 g
24.7 mL ? M
Concentration of NaOH solution (M)
Mass of H2C2O4 (g)
Volume of Added NaOH
Moles H2C2O4
Moles NaOH
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Buffers resist changes in pH

• Buffers contain large amount of an weak acid and
  its conjugate base
• HCl(aq) NaC2H3O2(aq) ?
• NaOH(aq) HC2H3O2(aq) ?
• Which of the following would constitute a buffer
  solution?
• (a) H2SO4 H2SO3(aq) (b)
  HF(aq) NaF(aq)
• (c) HCl NaCl (d)
  NaCl NaOH