Acids and bases, salts and solutions

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Acids and bases, salts and solutions

• Chapter 10-1 10-9, 11-1 11-4

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Key concepts

• Compare and contrast the Arrhenius and
  Brønsted-Lowry theories of acids and bases
• Describe hydrated protons
• Properties of acid and base solutions
• Arrange acids according to acid strength
• Balance acid-base equations
• Amphoterism
• Lewis acid-base theory
• Molarity calculations in titrations
• Equivalents

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Various properties of acids and bases
Acids Bases
Taste Sour (e.g., vinegar, citrus) Bitter (e.g., baking soda)
Indicators Litmus paper red Phenophthalein clear Litmus paper blue Phenophthalein pink/purple
Reactivity w/ metals Reacts w/ metals above H in activity series to produce H2 (g) Normally non-reactive
Reactivity w/MO, MOH React to form salt H2O Metal hydroxides are bases
Other rxns Strong acid weak acid salt ? weak acid strong acid salt Reacts with lipids (soap grease) Acid base ? salt water
conductivity Electrolytic solution Electrolytic solution
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Arrhenius theory of acids/bases

• Developed in 1884.
• An acid is a substance containing hydrogen that
  produces _______ in aqueous solution.
• A base is a substance containing the OH group
  that produces _______ in aqueous solution.

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Protons are not alone.

• Protons combine with water molecules to form
  __________ ___________.
• We commonly represent this as the hydronium ion,
  H3O(aq), but writing H(aq) means the same thing.

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Brønsted-Lowry theory (1923)

• An acid is a _______ _________.
• A base is a ________ __________.
• Bases are no longer restricted to compounds that
  release OH- in solution. For instance, NH3 is a
  base. What does it look like after reacting with
  a proton?

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Ionization of weak acids/bases

• While strong acids dissociate completely, not all
  reactions are complete and irreversible (in fact,
  most are not).
• Rxns with weak acids/bases are reversible.
  Example HF H2O
• What is the acid? What is the base? (depends on
  which side of rxn you look at)

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Conjugate acid-base pairs

• Conjugate acid-base pairs differ in structure by
  ___ _________.
• Some examples of conjugate pairs

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Acid/base strength

• The strength of an acid is _______ proportional
  to the strength of its base.
• Strong acids have ________________.
• Weaker acids have ________________. As the acid
  gets weaker and weaker, what happens to the
  conjugate base? What does this tell you about
  the amount of ionization taking place?

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Amphoterism

• Some substances can both give and accept protons.
  This process is called amphoterism.
• Water is the prime example of amphiprotic
  behavior.
• 2H2O ? H3O OH-

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Acid strength

• The hydrohalic acids HF, HCl, HBr, HI
• What are the sizes of the halogens? How will
  this affect the H-X bond?
• HF bond is very strong vs. the other halogens.
• F- causes ordering of the H2O molecules (how does
  that happen?)

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Leveling solvents

• In aqueous solution, no acid is stronger than
  H3O(aq). All other acids completely dissolve in
  water to form H3O.
• Because of this, all strong acids are of equal
  strength in water.
• A similar effect is observed for strong bases,
  which completely dissolve to form OH-.

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Ternary acids and bases

• What is a ternary acid?
• Ternary acids are hydroxyl compounds of a
  ______________.
• Ionize to produce H.

• Compare to other hydroxyl compounds
• Metal hydroxidesionize to produce
  ________________ and are ________ in aqueous
  solution.

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Ternary acid strength

• H2SO4 vs H2SO3. Whats the difference in acid
  strength?
• Compare oxidation number of sulfur in each.
• Acid strength increases with _______ oxidation
  number of the central atom.
• Order the following acids from weakest to
  strongest
• HBrO3, HBrO, HBrO4, HBrO2

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important!

• When comparing ternary acid strength, make sure
  the compounds have similar structure.
• Where are the hydrogens located?
• (H3PO3 vs H3PO4)

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Neutralization of Brønsted-Lowry acids/bases

• HA MB ? HB MA
• In many cases, HB ends up being ______.
• Classic example strong acid strong base.
• What happens in the reaction of hydrochloric acid
  and sodium hydroxide?
• What is the net ionic equation?

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Weak acid strong base

• General reaction
• HxA (aq) x OH- (aq) ? A- (aq) x H2O (l)
• When does x vary?
• Examples

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Acid salts

• Acid salts are salts of ______ acids that still
  contain __________ ___________.

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Lewis theory

• The most general of all acid-base theories
• Discards the proton acceptor/donator all
  together.
• A Lewis acid _______ a share in an electron pair.
• A Lewis base _________ a share in an electron
  pair.
• Lewis acids and bases are neutralized when a
  ________ _______ forms.

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When is Lewis theory used?
Arrhenius or B-L theory a better description for
most aqueous solns
LEWIS THEORY
Bronsted- Lowry
Arrhenius
Lewis theory a good descriptor for
nonaqueous solvents or transition metals
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Acid-Base calculations

• Molarity calculations play an important part in
  acid-base reaction stoichiometry
• Much of what we will learned in Chapter 3 will be
  used here.

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Molarity

• M mol/L or
• M mmol/mL
• we can use moles and liters, or millimoles and
  milliliters, and the molarity is still the same.

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Similarities between acid-base and other reaction
calculations

• We still compare moles to moles, not volumes to
  volumes or molarities to molarities.
• Additionally, knowing the limiting reactant is
  very important (i.e, what will run out firstacid
  or base?)

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Some examples

• what volume of 0.800 M NH3 is required to
  neutralize 22.0 mL of 12.0 M HCl?
• 25.0 mL of 0.0500 M Ca(OH)2 added to 10.0 mL of
  HNO3.
• Is the solution now acidic or basic?
• how many moles excess acid or base are in the
  solution?
• how much additional Ca(OH)2 or HNO3 soln
  required to neutralize solution?

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TITRATIONS

• Combining a known concentration with an unknown
  concentration solution.
• Titrant The solution of one reactant (usually
  of unknown concentration) that is carefully added
  to the solution of the other reactant until the
  resulting solution is just neutralized (no excess
  acid or base).
• How do we know when to stop?

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Titrations (cont)

• indicators
• How to measure the volume of titrant?
• Buret
• equivalence point The point where _____________
  _______________ amounts of acid and base have
  reacted.
• end point The point where the indicator
  ____________ ___________.
• For accurate work, one wants the end point and
  equivalence point to coincide with each other.

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Primary and secondary standards

• Reading on standardization your text goes over
  the requirements of a primary standard. You
  should be familiar with these requirements.
• Primary standards are used to determine the
  concentration of solutions, which become
  secondary standards.
• Example KHP and NaOH.

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EQUIVALENT WEIGHTS AND NORMALITY

• One mole of acid is _____________________________
• But, one equivalent of acid contains
  ______________________________.
• The equivalent weight, then, corresponds to molar
  mass/( of equ./mol)

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normality

• number of equivalents per liter, or N eq/L
  meq/mL
• N M ? eq/mol
• Lets do a couple of examples

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EQUIVALENTS in acid/base reactions

• 1 eq acid always reacts with 1 eq base.
• Va Na Vb Nb