Chapter 18 - Acids and Bases Notes
I. Properties of Acids and Bases
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ACIDS
1.
2.
3.
4.
5.
Taste sour
Reach with certain metals (Zn, Fe, etc.) to produce hydrogen gas
cause certain organic dyes to change color
react with limestone (CaCO3) to produce carbon dioxide
React with bases to form salts and water
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BASES
1.
2.
3.
4.
5.
Taste bitter
feel slippery or soapy
react with oils and grease
cause certain organic dyes to change color
react with acids to form salts and water
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Define:
o
o
Acid - a substance that produces protons, H+
Base - a substance that produces hydroxide ions, OH-
II. Reaction of acids and bases with water:
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Acids and bases form ions in solution:
HCl(aq)  H+(aq) + Cl-(aq)
H3O+ - hydronium ion H+ and H3O+ are equivalent in aq. solution
When we look at the reactions of acids - can be generalized using hydrogen ion
1. Reaction with zinc yields hydrogen gas
2. Reaction with limestone - produce CO2(g)
3. Acids react with bases to produce a salt
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Similarly for bases, produce hydroxide ions
III. Neutralization and Salts
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Neutralization - one type of double replacement reaction
Acid + Base  Salt + water
Net ionic equation shows what drives the neutralization reaction
example:
Molecular: HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
Total Ionic: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)  Na+(aq) + Cl-(aq) + H2O(l)
Net Ionic: H+(aq) + OH-(aq)  H2O(l)
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SALT - a salt is formed from the anion of the acid and the cation of the base - usually
present as spectator ions. - not always NaCl
IV. Types of Acids
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Monoprotic - a solution that produces one mole of H+ ions per mole of acid
HCl , HNO3
Diprotic - a solution that produces two moles of H+ ions per mole of acid
H2SO4
Triprotic - a solution that produces three moles of H+ ions per mole of acid
H3PO4
Polyprotic - two ore more H+ per mole of acid
V. Polyprotic acids:
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can be Partially neutralized
acid salt - an ionic compound containing the anion with one or more hydrogens that can
be neutralized with a base
VI. Strengths of Acids and Bases:
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STRONG ACIDS
o Acids that are essentially 100% ionized in aqueous solutions
o ex: HCl, HNO3, HClO4
o produce the maximum concentration of H+
o [acid] = [H+]
WEAK ACIDS
o Acids that are partially ionized ( usually less than 5%) in equilibrium.
o
o
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HF + H2O(l)
H3O+(aq) + F-(aq)
The forward and the reverse reaction are occurring simultaneously most found as
HF.
STRONG BASES
o those compounds that completely ionize in water to produce OH- ions
o NaOH(s)  Na+(aq) + OH-(aq)
o Concentration of base = concentration of hydroxide ions
WEAK BASES
o
o
NH3(aq) + H2O(l)
NH4+(aq) + OH-(aq)
equilibrium lies far to the left (mostly reactants present)
VII. Equilibrium of Water
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H2O(l) + H2O(l)
H3O+(aq) + OH-(aq)
Autoionization - produces positive and negative ions from the dissociation of the
molecules of a liquid.
Experimentally, found concentration of ions = 1.0 x 10-7 M at 25 C
[H3O+][OH-] = Kw
at 25 C (1.0 x 10-7)(1.0 x 10-7) = 1.0 x 10-14
Kw = ION PRODUCT - gives us the concentrations of hydronium and hydroxide ions in
pure water and acidic and basic solutions
Neutral
[H3O+] = [OH-] = 1.0 x 10-7 M
Acidic
[H3O+] > 1.0 x 10-7, [OH-] <1.0 x 10-7
Basic
[H3O+] < 1.0 x 10-7, [OH-] >1.0 x 10-7
VIII. pH Scale - another way of writing concentrations.
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pH = -log[H3O+] pOH = -log[OH-]
pH = 1.00  [H3O+] = 1.0 x 10-1M
pH = 7.00  [H3O+] = 1.0 x 10-7M
Sig. Figs:
1. The number of sig figs to the right of decimal in pH equals the number of total sig. figs.
in the concentration.
2. The total number of sig. figs. in the concentration equals the number of sig. figs. to the
right of the decimal in the pH.
IX. Similarly for hydroxide
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pOH = -log[OH-]
pOH = 1.00  [OH-] = 1.0 x 10-1M
pOH = 7.00  [OH -] = 1.0 x 10-7M
pH + pOH = 14.000
Neutral
pH = 7
pOH = 7
Acidic
pH < 7
pOH > 7
Basic
pH > 7
pOH < 7
X. Brønsted-Lowry Acids and Bases
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acid - a proton (H+) donor
base - a proton (H+) acceptor
NH3(aq) + H2O(aq)  NH4+(aq) + OH- (aq)
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NH3 and NH4+ are conjugate acid-base pairs
H2O and OH- are conjugate acid-base pairs
Amphiprotic - a compound or ion that can either donate or accept H+ ions.
H2O, HSO4- , HPO42-, HSO3- etc.
XI. Predicating acid base reactions in water:
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Acid-Base reactions always yield conj. acid-base
Strong Acid  weak conj. base
Strong Base  weak conj. acid
Weak Acid  strong conj. base
Weak Base  strong conj. acid
The strength of the reactant compared to the strength in the product determines which
direction the equilibrium lies.
Three predictions can be made:
o The reactant may Not react at all, leaving essentially all reactants (negligible)
o The reactants may Slightly react, leaving mostly reactants (limited)
o The reactants may react (essentially) completely, leaving little or no reactants
(favorable)
XI. Acidic and Basic Salt solutions:
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Hydrolysis - the reaction of an anion with water to produce OH- or the reaction of a
cation to produce H3O+ .
Neutral solutions of salts: Cation does not undergo hydrolysis
Anion does not undergo hydrolysis
Basic solutions of salts: Cation same as above
Anion undergoes some hydrolysis
Acidic solutions of salts: Cation undergoes some hydrolysis
Anion does not
Complex solutions: Cation and anion undergoes hydrolysis
Then you need to know the relative strength of each.
XII. Buffer solutions
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Buffer solution - resists changes in pH caused by the addition of limited amounts of a
strong acid or a strong base.
A buffer solution must contain:
A weak acid + its conjugate base
or A weak base + its conjugate acid