Acids and Bases

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Acids and Bases
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Ionization of Water

• Only happens to a small amount of water molecules
• H2O separates into H and OH-
• Not the whole story
• H never occurs on its own
• In reality, another H2O molecule picks it up and
  becomes H3O (hydronium ion)

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Acids and Bases
Acids Bases
Taste sour Taste bitter
Feel watery Feel slippery
Conduct electricity Conduct electricity
Change litmus to red Change litmus to blue
pH 0-7 pH 7-14
Neutralize bases Neutralize acids
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Classifying Acids and Bases

• Arrhenius
• Acid- substance that dissociates into H and an
  anion
• For Example HCl and H2SO4
• Base- substance that dissociates into cation and
  OH-
• For example NaOH and Mg(OH)2
• Does not explain bases without an OH ion

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Classifying Acids and Bases (cont)

• Brønsted-Lowry
• Acid - Proton (H) donor
• For example HCl and H2SO4
• Base - Proton (H) acceptor
• For example NH3 and OH-

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Conjugate Acid and Bases

• Occur on the other side of acid base equations.
• Lets look again at
• NH3 is a base. It will accept a proton (H)
• H2O is an acid. It will donate a proton (H)
• NH4 is NH3s conjugate acid. It can donate a
  proton (H) to become NH3 again
• OH- is waters conjugate base. It can accept a
  proton (H) to become H2O again

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Amphiprotic

• Amphiprotic
• Substances that can act like an acid or a base
• Water is an amphiprotic substance.
• H2O can accept a proton to become H3O
• H2O can donate a proton to become OH-

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Strength of Acids and Bases

• Depends on how much they dissociate in water
• Strong
• Considered to dissociate completely in water
• Weak
• Only partially dissociate in water
• Reaction is reversible (?)
• Conjugate pairs
• Strength is inversely proportional
• For example Strong acids have weak conjugate
  bases

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Acids

• Strong acids
• HI
• HBr
• HCl
• HNO3
• H2SO4
• HClO4
• HClO3
• All have 100 of the molecules break apart.
  There is no reverse reaction.
• Weak acids
• All others

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Polyprotic Acids

• Have multiple Hs
• H2SO4
• H2SO4 gives up 1 H to form HSO4-
• This happens to 100 of the molecules since H2SO4
  is strong
• HSO4- gives up another H to form SO4-2
• This only happens to some HSO4- because it is
  weak
• Solution will contain
• A lot of water molecules
• H3O molecules (mostly from the first H but some
  from the second and from ionization of water)
• HSO4-
• a little bit of SO4-2
• A little bit of OH- (from the ionization of water)

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Acid Names

• Binary acids (H with an element)
• Prefix hydro-
• Root of element name
• Suffix ic
• Add acid
• For example HCl is hydrochloric acid
• Acids with Oxygen (H with a polyatomic)
• Root name of polyatomic (with polyatomic prefix
  if applicable)
• Some polyatomic roots are modified slightly to be
  easier to say
• Suffix
• -ic with polyatomics ending in ate
• -ous with polyatomics ending in -ite
• Add acid
• For example H2SO4 is sulfuric acid

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Bases

• Strong bases
• Group 1 metals with OH-
• Ca, Sr, and Ba with OH-
• These three are not very soluble in water, but
  the amount that does dissolve ionizes completely.
• Weak bases
• All others

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Chemical Equilibrium

• Reversible reactions
• Indicated with a ?
• Both reactions are happening at the same time
• System reaches equilibrium when both are
  happening at same rate
• At equilibrium
• Could have lots of reactant and little product
• Could have lots of product and little reactant
• Could have equal amounts of both
• Changes to the system can shift equilibrium
• Temperature
• Pressure
• Adding reactants or products

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Equilibrium Expressions

• Mathematical way to represent equilibrium
• For the equation, aA bB ? cC dD
• K Cc Dd
• Aa Bb
• K is the equilibrium constant for the equation
• indicates the concentration of each substance
  in mol/L (M)
• Solid and pure liquids are not entered into the
  expression

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Ionization of Water

• 2H2O(l) ? H3O(aq) OH-(aq)
• This equilibrium lies to the left
• In other words, there is far more water molecules
  than hydronium and hydroxide ions in a sample
• Kw H3O OH-
• Kw 1.0 x 10-14
• In pure water and neutral solutions, H3O and
  OH- are 1.0 x 10-7 M
• In acidic solutions, H3O is greater than OH-
• In basic solutions OH- is greater than H3O

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pH

• pH
• Stands for potential of Hydrogen (really
  hydronium)
• Logarithmic scale
• pH -log H or H 10-pH
• Values between 0-14 with each number representing
  a 10-fold increase from the previous number
• pH ? 7 is acidic
• pH 7 is neutral
• pH ? 7 is basic

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pOH

• pOH -log OH- or OH- 10-pOH
• Opposite scale
• pOH ? 7 is basic
• pOH 7 is neutral
• pOH ? 7 is acidic

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Indicators

• Compounds that change color in the presence of
  different levels of pH

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Soil pH 5.0-5.5
Soil pH 6.0-6.5
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Neutralization (Acid-Base Reaction)

• Special type of double displacement reaction
• Acid Base ? Water Salt

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Titration

• Process of neutralizing an acid (or base) with an
  unknown concentration with a base (or acid) of a
  known concentration
• Moles of H3O must equal moles of OH- for
  neutralization to occur
• Often indicators are used to determine the end of
  the reaction
• VaMa VbMb
• Va volume in L of acid
• Ma molarity of acid
• Vb volume in L of base
• Mb molarity of base