IONIC COMPOUNDS
Compounds in Aqueous Solution
Many reactions involve ionic compounds,
especially reactions in water — aqueous
solutions.
KMnO4 in water
K+(aq)
aq) + MnO4-(aq)
aq)
Aqueous Solutions
How do we know ions are present in aqueous
solutions?
The solutions conduct electricity!
ClNegative
O atom
Na+
They are called ELECTROLYTES
HCl,
HCl, KMnO4, MgCl 2, and NaCl are strong
electrolytes. They dissociate completely
(or nearly so) into ions.
KMnO4(aq)
aq) ---> K+(aq)
aq) + MnO4-(aq)
aq)
Positive
H atom
NaCl dissolving
in water
Aqueous Solutions
Aqueous Solutions
Aqueous Solutions
How do we know ions are present in aqueous
solutions?
The solutions conduct electricity!
Acetic acid ionizes only to a small extent, so
it is a weak electrolyte.
Acetic acid ionizes only to a small extent, so
it is a weak electrolyte.
They are called ELECTROLYTES
CH3CO2H(aq
H(aq))
---> CH 3CO2-(aq)
aq) + H+(aq)
aq)
CH3CO2H(aq
H(aq))
---> CH 3CO2-(aq)
aq) + H+(aq)
aq)
HCl,
HCl, MgCl 2, and NaCl are strong
electrolytes. They dissociate completely
(or nearly so) into ions.
+
Page 1
Acetic acid — Weak Electrolyte
Ionized
acetic
acid
H+
WATER SOLUBILITY OF
IONIC COMPOUNDS
Not all ionic compounds dissolve in
water. Some are INSOLUBLE .
See Screen 4.6 and Figure 5.4
Aqueous Solutions
Nonelectrolyte— Ethanol, C 2H5OH
Some compounds dissolve in water but
do not conduct electricity. They are
called nonelectrolytes.
nonelectrolytes.
Examples include:
sugar
ethanol
ethylene glycol
(in antifreeze)
WATER SOLUBILITY OF IONIC
COMPOUNDS
Common minerals are often formed with
anions that lead to insolubility:
sulfide
fluoride
carbonate
oxide
As long as one ion from the list is
present in a compound, the
compound is water soluble.
Iron pyrite, a sulfide
Azurite, a copper
carbonate
Page 2
Orpiment,
arsenic sulfide
ACIDS
ACIDS
An
An acid
acid ------->
-------> H
H++ in
in water
water
Some strong acids are
HCl
hydrochloric
H2SO4
sulfuric
HClO 4
perchloric
HNO3
nitric
HNO3
ACIDS
ACIDS
An
An acid
acid ------->
-------> H
H++ in
in water
water
HCl(
HCl(aq)
aq) ---> H+(aq)
aq) + Cl-(aq)
aq)
Weak
Weak Acids
Acids
The
The
Nature
Nature of
of
Water
Water
HCl
Cl-
H2O
hydronium
ion
ACIDS
ACIDS
H3O+
The
The
Nature
Nature
of
of
Acids
Acids
BASES
see
see Screen
Screen 4.8
4.8 and
and Table
Table 4.1
4.1
Nonmetal oxides can be acids
CO2(aq)
aq) + H2O(liq
O(liq))
---> H 2CO3(aq)
aq)
SO3(aq)
aq) + H2O(liq
O(liq))
---> H 2SO4(aq)
aq)
and can come from burning
coal and oil.
Base
Base --->
---> OH
OH-- in
in water
water
NaOH(
NaOH(aq)
aq)
---> Na+(aq)
aq) + OH-(aq)
aq)
NaOH is
a strong
base
Page 3
WEAK ACIDS = weak
electrolytes
CH3CO2H
acetic acid
H2CO3
carbonic acid
H3PO4
phosphoric acid
Ammonia, NH3
An Important Base
NH3(aq)
aq) + H 2O(liq
O(liq))
---> NH 4+( aq)
aq) + OH -(aq)
aq)
BASES
BASES
Metal oxides are
bases
CaO(s)
CaO(s) + H 2O(liq
O(liq))
--> Ca(OH) 2(aq)
aq)
Net Ionic
Equations
Mg(s) + 2 HCl(
HCl(aq)
aq) --> H2(g) + MgCl 2(aq)
aq)
Net
Net Ionic
Ionic Equations
Equations
Mg(s) + 2 HCl(
HCl(aq)
aq)
--> H2(g) + MgCl 2(aq)
aq)
Mg(s) + 2 H +(aq)
aq) + 2 Cl-(aq)
aq)
---> H 2(g) + Mg 2+(aq)
aq) + 2 Cl-(aq)
aq)
We really should write
Mg(s) + 2 H +(aq)
aq) + 2 Cl-(aq)
aq) --->
H2(g) + Mg 2+(aq)
aq) + 2 Cl-(aq)
aq)
CaO in water. Indicator
shows solution is basic.
The two Cl- ions are SPECTATOR IONS —
they do not participate. Could have used NO 3-.
Page 4
We leave the spectator ions out —
Mg(s) + 2 H+(aq)
aq) ---> H 2(g) + Mg2+(aq)
aq)
to give the NET
IONIC EQUATION