10.2 THEORETICAL ACID-BASE DEFINITIONS
ARRHENIUS THEORY OF ACIDS AND BASES


Swedish chemist, Svante Arrhenius was studying a theory where
he began to propose the conductivity of acids and bases in
solutions. He suggested that since acids and bases conducted
electricity, they must contain ions. He proposed the following:
An acid is a molecular compound that ionizes in water to
produce one or more hydrogen ions (H+)
H2SO4(aq) 
Dissociation Equation:

A base is an ionic compound that dissociates in water to form
one or more hydroxide ions (OH-).
Ionization Equation:
Ca(OH)2(aq) 
Dissociation
Ionization
Difference
Similarity
NEUTRALIZATION REACTIONS
Write a ionization (same as dissociation equation) for HCl(aq):
Write a dissociation equation for NaOH(aq):
Write a total ionic equation for this reaction:
Write a net ionic equation for this reaction:
Problems with the Theory:
 Chemists leave out water in the reaction to form an acid and a base.
 Ammonia (NH3) does not look like it dissociates into hydroxide ions, but it’s a base. However, if
you react ammonia with water, hydroxide ions result.
NH3(g) + H2O(l)  NH4+(aq) + OH-(aq)
 The problem is that the Arrhenius theory is limited to acid-base reactions that occur in water.
STRONG AND WEAK ACIDS AND BASES
The relative strength of an acid or base depends upon the degree to which it ionizes/dissociates in
solution.
Strong acids and strong bases
in an aqueous solution. This gives rise
to its strong acidic properties (low pH and high reactivity) and basic properties (high pH and high
reactivity) . Weak acids and bases
in an aqueous solution. Thus,
only a small percentage (approx. 2%) of the acid or base molecules break apart into ions.
Strong Acids and Bases
Examples: HCl(aq)  H+(aq) + Cl-(aq)
KOH(aq)  OH-(aq) + K+(aq)
Weak Acids and Bases
Ex. HC2H3O2  H+(aq) + C2H3O2-(aq)
(Partial Ionization)
pH (Power of Hydrogen) (pH chart on following page)
 The pH scale is a numerical scale from 0-14, demonstrating the strength of various acids and
bases. Acids have a pH
. Bases have a pH
and neutral
substance has a pH
.
 A change in one pH unit represents a
in the strength of that acid of
base. For example, a solution with a pH of 14 is
times more basic than a
solution with a pH of 10. The solution with a pH of 10 is 104 times more
than
a solution with a pH of 14.
Advantages and Disadvantages of pH Changes
 Living things cannot tolerate large changes in pH, including the human body. The enzymes and
other proteins in the body have an optimal pH. Anything that goes against this optimal pH
causes proteins to denature and not function properly, resulting in drastic health effects.
 The shampoos we use are slightly acidic and help protect the outer covering of hair strands.
This makes hair smoother and less likely to tangle
Homework: Read Page 470-474 Page 475 #1-12
STRONG ACID
WEAK BASE
NEUTRAL
WEAK ACID
STRONG BASE
THE pH SCALE