Transcript Slide 1

Three models of acids:
l. Arrhenius Model Basis for the model--action in water
acid definition: produces H in water solution
base definition: produces OH1- in water solution
2. Bronsted-Lowry Model
Basis for the model-- proton transfer
acid definition: donates a proton ( H )
base definition: accepts a proton
conjugate acid definition: the acid becomes the conjugate base after it
donates the proton because it can now accept it back. conjugate base
definition: the base becomes the conjugate acid after it accepts the
proton because it can now donate it back.
3. Lewis Model
Basis for model--electron pair transfer
acid definition: accepts a pair of electrons
base definition: donates a pair of electrons
Acids:
• react with zinc, magnesium, or aluminum and form
hydrogen (H2(g))
• react with compounds containing CO32- and form
carbon dioxide and water
• turn litmus red
• taste sour (lemons contain citric acid, for example) DO
NOT TASTE ACIDS IN THE LABORATORY!!
Bases:
• feel soapy or slippery
• turn litmus blue
• they react with most cations to precipitate hydroxides
• taste bitter (ever get soap in your mouth?) DO NOT
TASTE BASES IN THE LABORATORY!!
• Water dissociation: H2O(l) → H+(aq) + OH-(aq)
Definitions of acidic, basic, and neutral solutions
based on [H+]
• acidic: if [H+] is greater than 1 x 10-7 M
basic: if [H+] is less than1 x 10-7 M
neutral: if [H+] if equal to 1 x 10-7 M
pH
• relationship between [H+] and pH
• pH = -log10[H+]
• Definition of acidic, basic, and neutral
solutions based on pH
• acidic: if pH is less than 7
basic: if pH is greater than 7
neutral: if pH is equal to 7
Acids
1. Strong Acids:
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completely dissociate in water, forming H+ and an anion. example: HN03 dissociates completely in water to form
H+ and N031-.
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The reaction is
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HNO3(aq) → H+(aq) + N031-(aq)
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There are only 6 strong acids. The remainder of the acids therefore are considered weak acids.
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HCl
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H2SO4
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HNO3
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HClO4
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HBr
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HI
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Note: when a strong acid dissociates only one H+ ion is removed. H2S04 dissociates giving H+ and HS04- ions.
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H2SO4 → H+ + HSO412. Weak acids:
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a weak acid only partially dissociates in water to give H+ and the anion for example, HF dissociates in water to give
H+ and F-. It is a weak acid. with a dissociation equation that is
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HF(aq) ↔ H+(aq) + F-(aq)
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Note the use of the double arrow with the weak acid. That is because an equilibrium exists between the
dissociated ions and the undissociated molecule. In the case of a strong acid dissociating, only one arrow ( → ) is
required since the reaction goes virtually to completion.
1. Strong Bases:
• They dissociate 100% into the cation and OH- (hydroxide ion).
• example: NaOH(aq) → Na+(aq) + OH-(aq)
• Which are the strong bases? The hydroxides of Groups I and II.
2. Weak Bases:
• What compounds are considered to be weak bases?
• Most weak bases are anions of weak acids.
• Weak bases do not furnish OH- ions by dissociation. They react with water
to furnish the OH- ions.
• When a weak base reacts with water the OH- comes from the water and
the remaining H+ attaches itsef to the weak base, giving a weak acid as
one of the products. You may think of it as a two-step reaction similar to
the hydrolysis of water by cations to give acid solutions. examples:
• NH3(aq) + H2O(aq) → NH4+(aq) + OH-(aq)
• methylamine: CH3NH2(aq) + H20(l) → CH3NH3+(aq) + OH-(aq)
• acetate ion: C2H3O2-(aq) + H2O(aq) → HC2H302(aq) + OH-(aq)
• General reaction: weak base(aq) + H2O(aq) → weak acid(aq) + OH-(aq)
• Since the reaction does not go to completion relatively few OH- ions are
formed.
Acid-Base Reactions:
• Strong acid + strong base:
HCl + NaOH → NaCl + H2O
salt +water produced