ch1001.doc

Chapter 10. Reactions in Aqueous Solutions I: Acids, Bases and Salts

Svente August Arrhenius

1859 - 1927 (Stockholm)

Ostwald; Boltzman; van't Hoff

Nobel Prize 1903

"Electrical Conductivity

of Solutions"

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Acid

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Examples:

2 HCl(aq) + Mg(s) ® H₂(g) + MgCl₂(aq) magnesium chloride
3 H₂SO₄(aq) + 2 Al(s) ® 6 H₂(g) + Al₂(SO₄)₃(aq) aluminum sulfate
2 NaOH(aq) + 6 H₂O + 2 Al(s) ® 3H₂(g) + 2 NaAl(OH)₄ sodium aluminate

2 HCl(aq) + CaO(s) ® CaCl₂(aq) + H₂O

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HCl(aq) + CH₃COONa(aq) ® CH₃COOH(aq) + NaCl acetic acid

NaOH(aq) + HCl ® NaCl + H₂O
3 Ca(OH)₂(aq) + 2 H₃PO₄ ® Ca₃(PO₄)₂ + 6 H₂O

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Arrhenius definition of:

Terms revisited:

Review Sections 4-2; 4-5; 6-7

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EXAMPLES
Neutralization:
HCl(aq) + NaOH(aq) ® H₂O(l) + NaCl(aq) (formula unit)

[H⁺ (aq) + Cl^-(aq)] + [Na⁺(aq) + OH^-(aq)] ® [Na⁺(aq) + Cl^-(aq)] + H₂O(l) (total ionic)

H⁺(aq) + OH^-(aq) ® H₂O(l) (net ionic)

Strong Electrolyte:
HCl(g) + H₂O(l) ® H⁺(aq) + Cl^-(aq)

Weak electrolyte:
HF(g) + H₂O(l) ¬ ® H⁺(aq) + F^-(aq)

Strong bases:
[Na⁺ OH^-](s) + H₂O ® Na⁺(aq) + OH^-(aq)

Weak acid:
CH₃COOH(l) + H₂O ¬ ® CH₃COO^-(aq) + H⁺(aq)

acetic acid acetate proton

99% 1%

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In aqueous solution the proton or hydrogen ion is hydrated

H⁺(H₂O)_n where n ~ 4

HYDRONIUM ION, H₃O⁺

H⁺ will always imply a hydrated proton

H⁺ will always imply a hydrated hydronium ion

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Bronsted theory or Bronsted-Lowry theory

ACID: H⁺ proton donor
Any substance which by its own ionization or in a reaction can furnish a proton

BASE: H⁺ proton acceptor

· No great concentration of H⁺
· Acids surrender protons only to bases
Acid₁ + base₂ ¬ ® acid₂ + base₁

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An acid-base reaction involves the transfer of a proton from an acid to a base:

Conjugate acid-base pairs: differ by a proton

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BRONSTED THEORY EXAMPLES(proton donor-proton acceptor)

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AUTOIONIZATION of AMPHIPROTIC MOLECULE H₂O

H₂O + H₂O = H₃O⁺ + OH^--

H₂O = H⁺ + OH- (really a pair of equilibrium arrows

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Acid Strengths of Hydrohalic Acids in the gas phase:
HF(weakest acid) << HC l< HBr < HI (strongest acid)

Acid Strengths of Hydrohalic Acids aqueous solution of HX:
HF is weak
HCl, HBr, HI (100% ionized) all very strong.
Because of LEVELING EFFECT no differentiation in acid strengths is possible.

H₃O⁺ is the strongest acid in water solution

OH^- is the strongest base. In water: NH_2- + H₂O ® NH₃ + OH-

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(the = sign represents an equilibrium ; one arrow facing right over the other arrow facing left)

Relative Strengths of Conjugate Acid-Base Pairs
HClO₄ and HNO₃ are strong acids

HCN and H₂O are weak acids

NH₃ is a very weak acid

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(the = sign represents an equilibrium ; one arrow facing right over the other arrow facing left)

Some typical ionizations:

All of the above involve H₂O:

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(the = sign represents an equilibrium ; one arrow facing right over the other arrow facing left)

Reactions of ACIDS + BASES. All involve
H₃O⁺ + OH- = 2H₂O and usually form salts:

HCl + NaOH = NaCl + H₂O

CH₃COOH + NaOH = CH₃COONa + H₂O

Neutralization of Perchloric acid. Its Total Ionic Equation:
[H⁺_(aq) + ClO_{4- (aq)}] + [Na⁺_(aq) + OH- _(aq)] ® [Na⁺_(aq) + ClO_{4- (aq)}] + H₂O_(l)

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Neutralization of insoluble hydroxide. Example:
formula unit:
Mg(OH)₂(s) + 2 HCl(aq)® MgCl₂(aq) + 2H₂O(l)

total ionic:
Mg(OH)₂(s) + 2 [H⁺(aq) + Cl^-(aq)] ® [Mg²⁺(aq) + 2 Cl^-(aq)] 2 H₂O(l)

net ionic:
Mg(OH)₂(s) + 2 H⁺(aq) ® Mg²⁺(aq) + 2 H₂O(l)

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Focus on stoichiometry of neutralization
Neutralization Reactions formula unit examples

NaOH_(aq) + HBr_(aq) ® NaBr_(aq) + H₂O_(l)
2NaOH_(aq) + H₂SO_4(aq) ® Na₂SO_4(aq) + 2 H₂O_(l)
3NaOH_(aq) + H₃PO_4(aq) ® Na₃PO_4(aq) + 3 H₂O_(l)

Ba(OH)_2(aq) + 2 HBr_(aq) ® BaBr_2(aq) + 2 H₂O_(l)
Ba(OH)_2(aq) + H₂SO_4(aq) ® BaSO_{4 (s)} + 2 H₂O_(l)
3 Ba(OH)_2(aq) + 2 H₃PO_4(aq) ® Ba₃(PO₄)_2(s) + 6H₂O_(l)

NH_3(aq) + HBr_(aq) ® NH₄Br_(aq)
2 NH_3(aq) + H₂SO_4(aq) ® (NH₄)₂SO_4(aq)

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Acidic Salts: Not enough base added

formation of: sodium dihydrogen phosphate
H₃PO₄(aq) + NaOH(aq) ® NaH₂PO₄(aq) + H₂O(l)

formation of: disodium hydrogen phosphate
H₃PO₄(aq) + 2 NaOH(aq) ® Na₂HPO₄(aq) + 2H₂O(l)

formation of sodium phosphate (normal salt)
H₃PO₄(aq) + 3 NaOH(aq) ® Na₃PO₄(aq) +H₂O(l)

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Basic Salts: Not enough Acid added

formation of: Aluminum dihydroxide chloride
Al(OH)₃(s) + HCl(aq) ® Al(OH)₂Cl(s) + H₂O(l)

formation of: Aluminum hydroxide dichloride
Al(OH)₃(s)+2HCl(aq)® Al(OH)Cl₂(s) +2H₂O(l)

formation of: Aluminum chloride (normal salt)
Al(OH)₃(s)+3 HCl(aq) ® AlCl₃(aq) + 3 H₂O(l)

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Partial Neutralization
Sodium Hydroxide and sulfuric acid:

NaOH + H₂SO₄ ® H₂O + NaHSO₄ sodium bisulfate (acidic salt)

2 NaOH + H₂SO₄ ® 2 H₂O + Na₂SO₄ sodium sulfate (normal salt) strong electrolyte

KHP:is a Primary Standard in titrimetry.

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Normal, Acidic and Basic Salts

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Normal, Acidic and Basic Salts

From Dial Soap Label:

sodium tallowate, sodium cocoate,....

sodium chloride (NaCl), . titanium dioxide (TiO₂)

chromium hydroxide green (Cr(OH)₃)

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AMPHOTERIC SUBSTANCE: can react as an acid or base
AMPHIPROTIC SUBSTANCE:accept or donate a proton

Al(OH)_3(s) + 3 HCl_(aq) ® AlCl₃ + 3 H₂O
Al(OH)_3(s) + NaOH_(aq) ® NaAl(OH)_4(aq)

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PREPARATION of ACIDS

· Sulfuric acid + Salt: ® volatile acids: HCl, HBr, HI
H₂SO₄ + NaCl ® NaHSO₄ + HCl(g)
H₃PO₄ + NaCl ® NaH₂PO₄ + HCl(g) (sodium dihydrogen phosphate)

· Non-metal oxides + Water (no oxidation change)
SO₃ + H₂O ® H₂SO₄ ( sulfur trioxide; sulfuric acid
SO₂ + H₂O ® H₂SO₃ ( sulfur dioxide; sulfurous acid
Cl₂O₇ + H₂O ® 2 HClO₄ (dichlorine heptoxide; perchloric acid
(see page 231 for other examples)

· Non-metal halides + Water (hydrolysis)
phosphorus trichloride® phosphorous acid
PCl₃ + 3 H₂O ® 3 HCl + P(OH)₃

phosphorus pentachloride® phosphoric acid
PCl₅ + 4 H₂O ® O=P(OH)₃ + 5 HCl or written slightly differently
(OH)₃P(OH)₂ ® (OH)₃P=O + H₂O

ch1013arsenic(III)bromide arsenious hydroxide
AsBr₃ + 3 H₂O ® As(OH)₃ + 3 HBr (or H₃AsO₃)

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LEWIS

Oxidative addition accompanied by change in both electronic and molecular geometry

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Summary:

1 8268sum.doc

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In connection with the theory of conhugate acids and conjugate bases.

con·ju·gate (k¼n"j…-g³t") v. con·ju·gat·ed, con·ju·gat·ing, con·ju·gates. --tr. 1. Grammar. To inflect (a verb) in its forms for distinctions such as number, person, voice, mood, and tense. 2. To join together. --intr. 1. Biology. To undergo conjugation. 2. Grammar. To be inflected. --con·ju·gate (-g¹t, -g³t") adj. 1. Joined together, especially in a pair or pairs; coupled. 2. Mathematics & Physics. Inversely or oppositely related with respect to one of a group of otherwise identical properties, especially designating either or both of a pair of complex numbers differing only in the sign of the imaginary term. 3. Chemistry. Pertaining to an acid and a base that are related by the difference of a proton. --con·ju·gate (-g¹t, -g³t") n. Mathematics & Physics. Either of a pair of conjugate quantities. --con"ju·gate"ly adv. --con"ju·ga"tive adj. --con"ju·ga"tor n.