Chapter 6 Solutions, Acids, Bases

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ACIDS, BASES, AND pH

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Aqueous Solutions
How do we know ions are present?

• The solutions conduct electricity!
• They are called ELECTROLYTES
• HCl, MgCl2, and NaCl are strong electrolytes.
  They dissociate completely (or nearly so) into
  ions.

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Aqueous Solutions

• weak electrolyte,
• like Acetic acid, ionizes only to a small extent,
  
• CH3CO2H(aq) t
• CH3CO2-(aq) H(aq)

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Aqueous Solutions

• Some compounds dissolve in water but do not
  conduct electricity. They are called
  nonelectrolytes.

Examples include sugar ethanol ethylene glycol
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Acid Properties

• Sour taste (grape fruit)
• Found in many fruits
• Vinegar
• Will burn if not diluted
• Made up of Nonmetals
• Acid formulas usually start with hydrogen- ex
  HCl, H2SO4

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Base Properties

• Bitter taste
• Slippery feel
• Most household cleaners
• Also dangerous if not diluted
• Made up of a metal and nonmetals in formulas
• Arrhenius bases start with metals in their
  formulas and end with a OH- ex NaOH, KOH, Ba(OH)2

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Arrhenius Theory

• Substances ionize in water
• Acids, bases, and salts when dissolved in water,
  will conduct electricity.
• Called Electrolytes

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Arrhenius Theory

• Acids release hydrogen ions (H)
• HCl ? H Cl-
• Bases release hydroxide ions (OH-)
• NaOH ? Na OH-

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Strong and Weak Acids/Bases

• Generally divide acids and bases into STRONG or
  WEAK ones.
• STRONG ACID HNO3(aq) H2O(liq)
  ---gt H3O(aq) NO3-(aq)
• HNO3 is about 100 dissociated in water.

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Strong and Weak Acids/Bases
HNO3, HCl, H2SO4 and HClO4 are among the only
known strong acids.
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Strong Acids will completely ionize
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Strong and Weak Acids/Bases

• Weak acids are much less than 100 ionized in
  water.
• One of the best known is acetic acid CH3CO2H

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Strong and Weak Acids/Bases

• Strong Base 100 dissociated in water.
• NaOH(aq) ---gt Na(aq) OH-(aq)

Other common strong bases include KOH and
Ca(OH)2. CaO (lime) H2O --gt Ca(OH)2
(slaked lime)
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Strong and Weak Acids/Bases

• Weak base less than 100 ionized in water
• One of the best known weak bases is ammonia
• NH3(aq) H2O(liq) e NH4(aq) OH-(aq)

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ACID-BASE THEORIES

• The most general theory for common aqueous acids
  and bases is the BRØNSTED - LOWRY theory
• ACIDS DONATE H IONS
• BASES ACCEPT H IONS

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Bronsted Base adds one hydrogen ion
Reactants
Products

• Bronsted Acid removes one hydrogen ion

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ACID-BASE THEORIES

• NH3 is a BASE in water and water is itself an
  ACID

NH3 / NH4 is a conjugate pair related by the
gain or loss of H Every acid has a conjugate
base - and vice-versa.
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Conjugate Pairs
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You Practice

• NH3 H2O ? NH4 OH-
• HNO3 NaOH ? H2O NaNO3
• NaHCO3 HCl ? NaCl H2CO3

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Amphoteric

• A substance having the ability to act as an acid
  or a base

or AmphoPROTIC Hydrogen ion proton

• Water is an example

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Water is amphoprotic
It can gain and lose a H
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• Hydronium ion An ion formed when a free H
  forms with water to form an H3O

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Why is Water Neutral?
H3O OH-
When one water gains, another loses a H
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The pH scale only for water solutions
Basic more OH-
Neutral H3O OH-
Acidic more H3O
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Relative ion concentrations

• pH is a relative measure of the hydrogen ion
  concentration
• pH is a rating
• ranges from 0 14
• 0 most, 7 equal, 14 least

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Why at a pH 7 ?

• Determined by concentration X of each ion
• H OH- 10-7M
• The concentration of hydrogen ion equals the
  concentration of hydroxide ion equals ten to the
  negative seventh molar concentration

Need to remember molarity and concentration
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H3O, OH- and pH

• A common way to express acidity and basicity is
  with pH
• pH - log H3O
• In a neutral solution, H3O OH-
  1.00 x 10-7 at 25 oC
• pH -log (1.00 x 10-7) - (-7) 7

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Relative ion concentrations

• pOH is a relative measure of the hydroxide ion
  concentration
• pOH is a rating
• ranges from 0 14
• 0 most, 7 equal, 14 least

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Any pX Scales

• In general pX -log X
• pOH - log OH-
• pH - log H

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Determining pOH

• pH pOH 14
• If know one can determine the other.
• If pH 13, what is the pOH?
• 13 pOH 14

pOH 14 13 1