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ACID BASE Theories

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Arrhenius
acid: generates [H⁺] in solution ,  **[H⁺] and [H₃O⁺] are the same
base: generates [OH^-] in solution  (watch out for alcohols CH₃OH, not a base)

Bronsted-Lowry Model

The New York State Regents decide with their infinite wisdom, that the name "Bronsted-Lowry" is no longer important, so they angered all the chemistry teachers and decide to call it "the other acid base theory" on the exam.

acid: anything that donates a [H⁺] (proton donor)

base: anything that accepts a [H⁺] (proton acceptor)

 acid + base <=> acid + base

HNO₂ + H₂O <=> NO₂^- + H₃O⁺

Each acid has a conjugate base and each base has a conjugate acid. These conjugate pairs only differ by a proton. In this example: HNO₂ is the acid, H₂O is the base, NO₂^- is the conj. base, and H₃O⁺ is the conj. acid.

The Trick- Pick a compound on the left side of the equation.

Find the similar compound on the other side of the reaction. The species with 1 more Hydrogen is the acid, the one with less is the base.

HNO₂ <=> NO₂^-    or H₂O <=> H₃O⁺

So HNO₂ is the acid.    So H₃O⁺ is the acid.

The other is the base.

Past Regents Questions

Aug 2010-26 Which compound is an Arrhenius acid?
(1) CaO  (3) K₂O
(2) HCl   (4) NH₃

28 According to one acid-base theory, water acts as an acid when an H₂O molecule
(1) accepts an H⁺ (3) accepts an H^-
(2) donates an H⁺ (4) donates an H^-

June 2010-25 Which compound when dissolved in water is an Arrhenius acid?
(1) CH₃OH    (3) NaCl
(2) HCl           (4) NaOH

26 An acid can be defined as an
(1) H⁺ acceptor    (3) OH^- acceptor
(2) H⁺ donor        (4) OH^- donor

Jan 2010-25 When one compound dissolves in water, the only positive ion produced in the solution is H₃O⁺_(aq). This compound is classified as
(1) a salt
(2) a hydrocarbon
(3) an Arrhenius acid
(4) an Arrhenius base

Aug 2009-28 One acid-base theory defines a base as an
(1) H⁺ donor        (3) H donor
(2) H⁺ acceptor   (4) H acceptor

June 2009-28 One alternate acid-base theory states that an acid is an
(1) H+ donor       (3) OH- donor
(2) H+ acceptor   (4) OH- acceptor

Aug 2008-26 The Arrhenius theory explains the behavior of
(1) acids and bases
(2) alcohols and amines
(3) isomers and isotopes
(4) metals and nonmetals

Jan 2008-24 Which substance is an Arrhenius acid?
(1) Ba(OH)₂           (3) H₃PO₄
(2) CH₃COOCH₃   (4) NaCl

25 Which compound releases hydroxide ions in an aqueous solution?
(1) CH₃COOH    (3) HCl
(2) CH₃OH          (4) KOH

Aug 2007-27 Which compound is an Arrhenius acid?
(1) H₂SO₄     (3) NaOH
(2) KCl         (4) NH₃

Jun 2007-25 An Arrhenius base yields which ion as the only negative ion in an aqueous solution?
(1) hydride ion          (3) hydronium ion
(2) hydrogen ion       (4) hydroxide ion

26 According to one acid-base theory, a water molecule acts as an acid when the water molecule
(1) accepts an H⁺        (3) donates an H⁺
(2) accepts an OH^–     (4) donates an OH^–

Jan 2007-30 Which ion is the only negative ion produced by an Arrhenius base in water?
(1) NO^3–    (3) OH^–
(2) Cl^–        (4) H^–

June 2008-26 The Arrhenius theory explains the behavior of
(1) acids and bases
(2) alcohols and amines
(3) isomers and isotopes
(4) metals and nonmetals

June 2006-26 Which ion is the only negative ion present in an aqueous solution of an Arrhenius base?
(1) hydride ion     (3) hydronium ion
(2) hydrogen ion  (4) hydroxide ion

Aug 2006-26 The compound NaOH_(s) dissolves in water to yield
(1) hydroxide ions as the only negative ions
(2) hydroxide ions as the only positive ions
(3) hydronium ions as the only negative ions
(4) hydronium ions as the only positive ions

June 2005-28 When an Arrhenius acid dissolves in water, the
only positive ion in the solution is
(1) H⁺     (3) Na⁺
(2) Li⁺     (4) K⁺

Jan 2006-17 Which substance is an Arrhenius base?
(1) KCl        (3) KOH
(2) CH₃Cl    (4) CH₃OH

Aug 2005-49 How are HNO_3(aq) and CH₃COOH_(aq) similar?
(1) They are Arrhenius acids and they turn blue litmus red.
(2) They are Arrhenius acids and they turn red litmus blue.
(3) They are Arrhenius bases and they turn blue litmus red.
(4) They are Arrhenius bases and they turn red litmus blue.

Jan 2005-25 The compound HNO₃ can be described as an
(1) Arrhenius acid and an electrolyte
(2) Arrhenius acid and a nonelectrolyte
(3) Arrhenius base and an electrolyte
(4) Arrhenius base and a nonelectrolyte

Jan 2005-47 Which chemical equation represents the reaction of an Arrhenius acid and an Arrhenius base?
(1) HC₂H₃O_2(aq) + NaOH_(aq) �--> NaC₂H₃O_2(aq) + H₂O_(l)
(2) C₃H_8(g) + 5 O_2(g)�-->  3 CO_2(g) + 4 H₂O_(l)
(3) Zn_(s) + 2 HCl_(aq)�--> ZnCl_2(aq) + H_2(g)
(4) BaCl_2(aq) + Na₂SO_4(aq) ��--> BaSO_4(s) + 2 NaCl_(aq)

June 2004-29 Hydrogen chloride, HCl, is classified as an Arrhenius acid because it produces

(1) H⁺ ions in aqueous solution
(2) Cl^– ions in aqueous solution
(3) OH^– ions in aqueous solution
(4) NH₄⁺ ions in aqueous solution

AP Chemistry  The Lewis Model
acid: accepts an electron pair
base: donates an electron pair
The advantage of this theory is that many more reactions can be considered acid-base reactions because they do not have to occur in solution.

• F₃B  +  :NH₃ F₃B:NH₃ 

 

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