definition of acids traditional (arrhenius)- a chemical compound that contains hydrogen and...
DESCRIPTION
Bronsted-Lowry Acids expanded the Arrhenius definition by saying an acid is a molecule or ion that is a proton (H + ) donor So…Arrhenius acids donate protons to water but other substances can also donate protons Even water can act as a Bronsted-Lowry Acid H 2 O + NH 3 NH OH - TRANSCRIPT
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Definition of Acids
• Traditional (Arrhenius)- a chemical compound that contains hydrogen and ionizes in aqueous solutions to form hydrogen ions
Examples:HNO3 + H2O H3O+ + NO3
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Bronsted-Lowry Acids• expanded the Arrhenius definition by saying an
acid is a molecule or ion that is a proton (H+) donor
So…Arrhenius acids donate protons to water but other substances can also donate protons
Even water can act as a Bronsted-Lowry AcidH2O + NH3 NH4
+ + OH-
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Lewis Acids
• Allows substances that do not contain hydrogen to be considered acids
• A Lewis acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond
Example- Boron trifluorideBF3 + F- BF4
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Properties of Acids
• Sour taste• Produce predictable color changes in the
presence of an indicator• React with bases to produce salt and
water• Electrolytes• Some react with active metals releasing
hydrogen gas
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Strong vs. Weak Acids
• A strong acid ionizes completely in solution and as a result is a strong electrolyte
Examples: HBr, HCl see p. 474• Weak acids do not ionize completely in
solution and are weak electrolytes.Examples: HF, HCN see p. 474
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Common Acids and Uses
• Sulfuric Acid- battery acid, dehydrating agent
• Nitric Acid- explosives• Hydrochloric Acid- common lab acid,
pickling• Acetic Acid- vinegar
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Definition of Bases
• Traditional- a substance that contains hydroxide ions (OH-) and dissociates to give hydroxide ions in aqueous solutions
• Examples:NaOH Na+ + OH-
NH3 + H2O NH4+ + OH-
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• Bronsted-Lowry base- a molecule or ion that is a proton acceptor
• Lewis base- an atom, ion, or molecule that donates an electron pair to form a covalent bond
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Properties of Bases
• Bitter taste• Feel slippery• Produce predictable color changes in the
presence of an indicator• React with acids to produce salt and water• Electrolytes
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Strong vs. Weak Bases
• Strong bases dissociate completely in solution
KOH K+ + OH-
• Weak bases do not dissociate completelyNH3 + H2O NH4
+ + OH-
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pH Scale
• Ranges from 0 to 14• Values from 0 to 6.9 are acidic• Values from 7.1 to 14 are basic• A value of 7 is neutralMeasuring pH1. Indicators2. pH meters3. pH paper
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Neutralization Reactions
• The reaction of hydronium ions (H3O+) and hydroxide ions (OH-) to form water molecules
• The products of a neutralization reaction are neither acidic or basic but are neutral
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Example:HCl + NaOH NaCl + H2O
• Na+ and Cl- are only spectator ions (an ion that does not take part in a reaction and is found in solution both before and after the reaction)
• The reaction occurs between the hydronium ion (H3O+) and the hydroxide ion (OH-)
Net ionic eq. (H3O+ + OH- 2H2O)
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Salts
• Are formed from a neutralization reaction• Are ionic compounds composed of a metal
cation of an aqueous base and the anion from an aqueous acid
Example:H2SO4 + 2NaOH Na2SO4 + 2H2O
(acid) (base) (salt)
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Principles of Titration• A titration is the operation of gradually adding
one solution to another to reach an equivalence point ( the point at which a neutralization reaction is complete)
• Titrant- the solution added to another solution in a titration
• Standard solution- one whose concentration is accurately known
• End point- the point at which an indicator changes color
Read p.515-521
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Conjugate Acids/Bases• Conjugate base- the species that remains
after a Bronsted-Lowry acid has given up a proton
Example: HF + H2O F- + H3O+
acid conjugate base
Conjugate acid- the species that is formed when a Bronsted-Lowry base gains a proton
• Example: HF + H2O F- + H3O+
base conjugate acid
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Calculation of H3O+ and OH- Concentration
• Water will self-ionize to form hydronium and hydroxide ions in solution
H2O + H2O H3O+ + OH-
• Measurements show that the conc. of both
the hydronium ion and hydroxide ion in pure water are both equal to 1.0 x 10-7 M. Because their conc. are the same, pure water is a neutral
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Ionization Constant of Water
• Kw = [H3O+][OH-] = 1.0 x 10-14
Strong acids and bases completely ionize or dissociate to form H3O+ and OH- in solution so….
Conc. of a strong base = [OH-]Conc. of a strong acid = [H3O+]
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Example Problems
• A 1.0 x 10-4 M solution of HNO3 has been prepared. Calculate the hydronium ion conc. and the hydroxide ion conc.
• Determine the hydronium ion and hydroxide ion conc. in a solution that is
3.0 x 10-2 M NaOH.
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Calculating pH
• pH = -log[H3O+]Examples:1. What is the pH of a 1.0 x 10-3 M NaOH
solution?2. What is the pH of a 1.0 x 10-5 M HNO3
solution?
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Calculating [H3O+] and [OH-] from pH
• [H3O+] = 10-pH
Examples:1. The pH of a solution is 7.52.a. What is the hydronium ion conc.?b. What is the hydroxide ion conc.?c. Is the solution acidic or basic?