Terminology Note H + (aq) = H 3 O + or hydrogen ions in water
are equivalent to hydronium ions! Draw a hydronium ion
Slide 3
Acid-Base Theories There are three Acid-Base Theories Arrhenius
Bronsted-Lowry Lewis Arrheniusmost narrow Bronsted-Lowrybroader
than Arrhenius Lewismost broad
Slide 4
Arrhenius Arrhenius Acid: Arrhenius Base: those species that
ionize to produce H + ions (or hydronium ions) in water. Examples:
those species that ionize to produce OH -- ions in water.
Examples:
Slide 5
Bronsted-Lowry Bronsted Acid Bronsted Base H + (proton) donors
Examples: H + (proton) acceptors Examples:
Slide 6
Lewis Lewis Acid Lewis Base Electron Pair Acceptor Electron
Pair Donor This is an extremely wide definition of acids and bases.
This definition of acids and bases gets a new name and purpose in
organic chemistry. It is beyond the scope of high school
chemistry.
Slide 7
Relationship Between Definitions If a species is an acid under
the Arrhenius definition, then it is an acid under Bronsted-Lowry,
but the reverse is not automatically true.
Slide 8
Lets take a closer look:
Slide 9
Terms Associated with Bronsted-Lowry A/B _________________ is
the specie that is formed once the proton (H + ) has been accepted.
It is often abbreviated as CA. It is what the reactant base becomes
in the products. _________________ is the specie that remains after
the proton (H + ) has been donated. It is often abbreviated as CB.
It is what the reactant acid becomes in the products. An acid and
its conjugate base can be referred to as a conjugate acid-base
pair.
Slide 10
Generic Weak Acid Example HA + H 2 O H 3 O + + A-
Slide 11
Example 1 Identify the acid, base, conjugate acid, and
conjugate base for the following reactions: a) HI + H 2 O I- + H 3
O + b) H 2 O + HONH 3 + HONH 2 + H 3 O + c) NH 3 + H 2 O NH 4 + +
OH-
Slide 12
Strong Acids There are 5 strong acids: All other acids are weak
acids at some level. There are varying degrees of weakness. Strong
acids have weak conjugate bases, meaning that as a base, they have
a ___________________ for a proton (H + ). Weak acids ionize into
strong conjugate bases, meaning that as a base, they have a
_______________ for a proton. The strength of an acid is
_______________________ to the strength of its conjugate base.
Slide 13
Protic & Oxyacids Acids can be monoprotic, diprotic,
triprotic (or just polyprotic in general). Write two diprotic
acids. Most acids are oxyacids, meaning that the acidic proton is
attached to an oxygen atom. Oxyacids can be strong or weak acids,
but most are weak acids. Write two oxyacids.
Slide 14
Organic Acids Organic acids are acids that are primary
hydrocarbon chains and contain the carboxyl group, usually at the
end of the chain: Write one organic acid. O R-C-O-H R = generic
hydrocarbon This is the acidic H
Slide 15
Amphoterism Water is an ______________ substance, meaning it
can act as either an acid or a base. The autoionization of water
reaction is: H 2 O + H 2 O H 3 O + + OH- or H 2 O H + + OH-
Slide 16
Equilibrium Expression for Water The equilibrium expression for
water is called a K w K w = [H + ][OH-] = 1.0 x 10 -14 [H + ] means
the concentration of H + ions in _________ [OH-] means the
concentration of OH- ions in ____________
Slide 17
Acidity of Solutions A neutral solution is defined as one where
An acidic solution is defined as one where A basic solution is
defined as one where
Slide 18
Example 2 Are the following solutions acidic, basic, or
neutral? a) 0.01 M HCl b) 0.001 M NaOH c) 1.00 x 10 -7 M H 3 O
+
Slide 19
pH Scale The pH scale is simply a specific application of a
function. f(x) here is p(x). The p function means to take the log
of whatever comes after the p. For instance: pH = -log [H + ] =
-log [H 3 O + ] pOH = -log [OH-] pK w = -log K w Note that since
the p function is logarithmic, every whole number change in the pH
means a __________________ in the concentration.
Slide 20
Example 3 Calculate the pH of: a) 1.0 x 10 -3 M HCl b) 2.5 x 10
-4 M HClO 4 c) 5.9 x 10 -2 M NaOH
Slide 21
Example 4 If the pH of the acid is 6.9, calculate the
concentration of the hydronium ion.
Slide 22
Strong Bases Strong bases are hydroxide bases such as NaOH, or
KOH because they ionize (or dissociate) completely in water. Bases
do not have to contain hydroxide ions; they can be species that
will remove a proton from water, producing the hydroxide ion from
the water molecule. Other important relationships to note: pH + pOH
= pK w pH + pOH = 14
Slide 23
Example 5 Calculate the pH for a 1.50 M solution of KOH.
Slide 24
Slide 25
Concentration versus Strength Concentration Strength
Slide 26
Strong Weak
Slide 27
Comparing Concentration and Strength of Acids Acidic Solution
Concentration Strength Quantitative (Molarity) Relative
Hydrochloric Acid12 M HCl Gastric juice0.08 M HCl Ethanoic Acid17 M
CH 3 COOH Vinegar0.2 M CH 3 COOH
Slide 28
Strengths of Weak Acids (& Bases)
Slide 29
Acid Dissociation
Slide 30
Dissociation Constants For any reversible reaction, you can use
a balanced equation to express the equilibrium constant. The
equilibrium constant (K eq ) is the ratio of product concentrations
to reactant concentrations at equilibrium. The size of the
equilibrium constant indicates whether reactants or products are
more common at equilibrium. When K eq has a large value, the
reaction mixture at equilibrium will consist mainly of product.
When K eq has a small value, the mixture at equilibrium will
consist mainly of reactant. When K eq has an intermediate value,
the mixture will have significant amounts of both reactant and
product.
Slide 31
Acid Dissociation (K a ) For dilute aqueous solutions, the
concentration of water is a constant. This constant can be combined
with K eq to give an acid dissociation constant. An acid
dissociation constant (K a ) is the ratio of the concentration of
the substances in the reaction. The acid dissociation constant (K a
) reflects the fraction of an acid that is ionized. For this
reason, dissociation constants are sometimes called ionization
constants. If the degree of dissociation or ionization of the acid
in a solution is small, the value of the dissociation constant will
be small. Weak acids have small K a values. If the degree of
ionization of an acid is more complete, the value of K a will be
larger. ________________________________________________________
For example, nitrous acid (HNO 2 ) has a K a of 4.4 10 4, but
ethanoic acid (CH 3 COOH) has a K a of 1.8 10 5. This means that
nitrous acid is more ionized in solution than ethanoic acid.
Therefore, nitrous acid is a stronger acid than ethanoic acid.
Slide 32
K a Table
Slide 33
Base Dissociation (K b ) Base Dissociation Constant Just as
there are strong acids and weak acids, there are strong bases and
weak bases. A strong base dissociates completely into metal ions
and hydroxide ions in aqueous solution. Some strong bases, such as
calcium hydroxide and magnesium hydroxide, are not very soluble in
water. The small amounts of these bases that dissolve in water
dissociate completely. A weak base reacts with water to form the
conjugate acid of the base and hydroxide ions. For a weak base, the
amount of dissociation is relatively small. Ammonia is an example
of a weak base. In general, the base dissociation constant (K b )
is the ratio of the concentration of the conjugate acid times the
concentration of the hydroxide ion to the concentration of the
base. __________________________________________________