Acids and Bases
Hydrogen or hydroxide ions?
Acids and bases
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What are some general characteristics of
acids and bases?
Acids are sour.
 Bases are bitter and slippery.
 Acids are in many foods.
 Bases are good cleaners.
 They both conduct electricity in solution.
 Litmus turns red in acids and blue in bases.
 Acids react with metals.
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Acids and bases
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What makes an acid or a base?
Acids are water solutions that contain extra
hydrogen ions.
 Bases are water solutions that contain extra
hydroxide ions.
 Neutral solutions have equal numbers of both.
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Acids and bases.
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What is the Arrhenius model?
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Acids are substances that have hydrogen ions
to donate and bases have hydroxide ions to
donate.
 Examples:
 Doesn’t
HCl, NaOH, H2SO4,
explain NH3 or Na2CO3
Acids and Bases
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What is the Brønsted-Lowry model of
acids and bases?
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Acids are hydrogen ion donors and bases are
hydrogen ion acceptors.
 Examples:
HF, NH3, (water is amphoteric)
 Conjugate acids are formed when base accepts a
hydrogen ion and conjugate base is formed when
the acid donates its hydrogen ion.
Acids and bases
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What are Lewis acids and bases?
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The creator of the Lewis structures explains
an acid as an electron-pair acceptor and a
base as an electron pair donor.
Acids and bases
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What determines the strength of an acid or
base?
Strong acids ionize completely in solution.
This allows the maximum H ions.
 Weak acids ionize partially and lowers the
concentration of H ions.
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Acids and bases
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What is an acid (or base) ionization
constant?
This is the same as the equilibrium constant
only for the acid (or base) formation equation.
 Weak acids (or bases) have very low acid
ionization constants due to high concentration
of unionized molecules (reactants).
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Acids and bases
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How do we calculate ion concentrations?
pH = –log[H] or pOH = –log[OH]
 pH + pOH = 14
 What is the pH of a solution with a [OH] of
8.2 x 10-6 M?
 What is the [H+] of a solution with a pH of
9.1?
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Acids and bases
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What is Kw?
This is the ion product constant for water.
 It is always (at standard conditions) equal to
1.0 x 10-14.
 Kw = [H+][OH-]
 What is the pOH of a solution that has a H+
ion concentration of 1.0 x 10-5?
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Acids and bases
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What is Ka?
The ion constant for an acid (or base) is the
ratio of products to reactants in an equilibrium
situation.
 What is the Ka of .10 M HCOOH with a pH of
2.38?
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Acids and bases
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What is neutralization?
A reaction between an acid an base usually
produces a salt and water.
 This reaction returns the hydrogen and
hydroxide concentrations closer to normal.
 The hydrogen and hydroxide neutralize into
water.
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Acids and bases
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What is titration?
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Titration is a method of neutralizing an acid or base to
find the molar concentration.
This is done until an equivalence point is reached.
The equivalence point is where the hydrogen and
hydroxide ions are equal.
This is then solved using stoichiometry.
The end point is where the color of the indicator
changes. It needs to be at the same point as the
equivalence point to make sense.
Acids and Bases
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What is salt hydrolysis?
When salts dissociate into solution, some
anions become hydrogen acceptors (making
a higher OH- concentration) and some
become cations become hydrogen donors
(making a higher H+ concentration)
 The strength of the acid and base involved
will tell you the type of solution it will produce.
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Acids and bases
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How does the strength of the acid and
base determine the salt hydrolysis?
Strong acid and strong base make a neutral
salt.
 Strong acid and weak base make an acidic
salt.
 Weak acid and strong base make a basic salt.
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Acids and bases
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What is a buffer?
A buffer is a solution that will slow or resist the
change in pH because of Le Chatelier’s
principle.
 The buffer capacity is how much H+ or OH- a
solution can absorb without changing pH.
 pH is usually the –log[Ka]
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