CCR, page 177
An Ionic Compound,
CuCl2, in Water
Aqueous Solutions
How do we know ions are present
in aqueous solutions?
The solutions conduct
electricity!
They are called
ELECTROLYTES
HCl, CuCl2, and NaCl are
strong electrolytes.
They dissociate completely (or
nearly so) into ions.
Aqueous
Solutions
Acetic acid is a weak acid, it
ionizes only to a small
extent, so it is a weak
electrolyte.
CH3CO2H(aq) <--->
CH3CO2-(aq) + H+(aq)
ACIDS
Acids ---> H+ in water
HCl(aq)
HCl is a
strong
acid
---> H+(aq) + Cl-(aq)
Other strong acids
include:
HI, HBr, HNO3,
H2SO4, HClO4, HClO3
Weak acids
have H+ as
the cation,
and are not
STRONG
acids.
BASES
Base ---> OH- in water
NaOH(aq)
NaOH is a
strong
base
---> Na+(aq) + OH-(aq)
Other strong bases
include:
LiOH, KOH, RbOH,
CsOH, Ca(OH)2,
Ba(OH)2, Sr(OH)2
Weak bases
have OH- as the
anion, and are
not STRONG
bases.
Ammonia, NH3
An Important Weak Base
Memorize
Ammonia, NH3, as
a Weak Base!
Aqueous
Solutions
Some compounds dissolve in
water but do not conduct
electricity. These are
molecular compounds,
made of molecules, so they
do not split into charged
particles. They are called
nonelectrolytes.
Examples include:
sugar
ethanol
ethylene glycol
KISS Rules – Keep it Simple Solubility Rules
#1 – Soluble Cations: sodium, potassium, and ammonium
are always soluble
#2 – Soluble Anions – nitrate, acetate, chlorate,
perchlorate are always soluble
#3 – Soluble Anions – chloride, bromide, iodide are
soluble EXCEPT with the SILVER GROUP – silver,
mercury and lead
#4 – Soluble Anions – sulfate is soluble EXCEPT with
the Silver Group or with strontium or barium
#5 – EVERYTHING ELSE IS INSOLUBLE
Net Ionic
Equations
Mg(s) + 2 HCl(aq) --> H2(g) + MgCl2(aq)
Use your knowledge of Strong Electrolytes to determine what is Aqueous:
HCl is a strong acid, so it completely dissociates in water and can be written as
separate ions to show how it actually exists.
MgCl2 is soluble (KISS rules), so it completely dissociates in water and can be
written as separate ions to show how it actually exists.
We really should write:
Mg(s) + 2 H+(aq) + 2 Cl-(aq)
--->
H2(g) + Mg2+(aq) + 2 Cl-(aq)
The two Cl- ions are SPECTATOR IONS — they do
not participate. *Could have used NO3- instead and
the reaction would not have changed!
Net Ionic Equations
Mg(s) + 2 HCl(aq) --> H2(g) + MgCl2(aq)
Mg(s) + 2 H+(aq) + 2 Cl-(aq)  H2(g) + Mg2+(aq) + 2 Cl-(aq)
We leave the spectator ions out —
Mg(s) + 2 H+(aq) ---> H2(g) + Mg2+(aq)
to give the NET
IONIC EQUATION
Precipitation Reactions
The “driving force” is the formation of an insoluble
compound — a precipitate.
Pb(NO3)2(aq) + 2 KI(aq)  2 KNO3(aq) + PbI2(s)
Net ionic equation
Pb2+(aq) + 2 I-(aq)  PbI2(s)