Dissociation
In 1887, Svante August Arrhenius proposed that
when a substance dissolves in water, particles of
the substance separate from each other and
disperse into the solution (called dissociation).
Non-electrolytes disperse electrically neutral
particles (therefore don’t conduct electricity)
Electrolytes disperse electrically charged particles
called ions (therefore do conduct electricity)
Why do ionic compounds disperse
electrically charged particles?
The positive ions
are surrounded by
the negative end
of the polar water
molecules.
The negative ions
are surrounded by
the positive end
of the polar water
molecules.
RESULT: The ions at the edges of the
ionic crystal are tugged and dislodged
until each one is surrounded by water
molecules and is floating around as an
independent entity
DISSOCIATION – the separation of
ions that occurs when an ionic
compound dissolves in water
Dissociation Equations
Remember: There are two requirements of dissociation:
it must be soluble in water and must be ionic
Dissociation Equations:
shows the separation of ions in a chemical equation
H20(l) is not shown because it is a solvent and is NOT consumed nor changed.
It is shown in the aqueous states for the products (aq means “dissolved in
water”)
Examples: (you still need to make sure the equations are balanced)
NaCl(s)  Na + (aq) + Cl – (aq)
K3PO4(s) 
3 K +(aq) + PO43- (aq)
Try it on your own....
Pg. 198 #2
Arrhenius acids and bases
Arrhenius extended his dissociation theory to include acids and bases
Bases – ionic compounds containing the hydroxide ion (OH-) that
dissolve into cations and OH– (aq) in water
Ba(OH)2 (s)  Ba 2+ (aq) + 2 OH-(aq)
NOTE: All bases are ionic, so all bases could dissociate if soluble in H2O
Acids – molecular compounds containing hydrogen that yield H+ (aq) ions
when they dissolve in water
- Acids behave as molecular substances; CH3COOH (l) – does not conduct
electricity or change the color of litmus paper
- As soon as acids are dissolved in water, their acid properties appear;
CH3COOH (aq) will conduct electricity and changes litmus paper from blue to red
NOTE: Acids are not ionic, so they DO NOT dissociate. They IONIZE.
Arrhenius came up with the idea of ionization to explain
why acids are electrolytic:
The non-electrolytic molecular compound separates into
ions when dissolved in water, becoming electrolytic
HCl (g)  H+ (aq) + Cl-(aq)
IONIZATION – the reaction of neutral molecular
compounds forming charged ions
Dissociation vs. Ionization
What is the difference between dissociation and ionization?
Both produce (aq) ions...
Dissociation, however, is the separation of ions that already
exist before dissolving in water
M+X- (s)  M+ (aq) + X-(aq)
Ionization involves the production of new ions, specifically
hydrogen ions
HX0 (aq)  H+ (aq) + X-(aq)
SUMMARY
Substance
Process
General Equation
XY (s/l/g)  XY (aq)
Molecular
Disperse as individual,
neutral molecules
Ionic
Dissociate into individual
ions
MX (s)  M+ (aq) + X-(aq)
Base (ionic hydroxide)
Dissociate into positive
ions and hydroxide ions
MOH (s)  M+ (aq) + OH-(aq)
Acid
Ionize to form hydrogen
ions and anions
HX (s/l/g)  H+ (aq) + X-(aq)
Reference pg. 201
Solubility
IONIC
Use solubility table
MOLECULAR
Memorize
ACIDS
All soluble
BASES
Ionics 
Try it on your own...
Pg. 202 #1-3
Pg 195 Lab Exersice 5.A
Complete Analysis - Identities of solutions
Pg 195 Section 5.1 questions Q 3,5-7
Pg. 202 Q 1-4,8