General Properties of Aqueous Solution
and Precipitation Reactions
Jing Gu
Concepts you will learn in this class
Solution
Solute
Solvent
Electrolyte:
-Strong electrolyte
-Weak electrolyte
-Non electrolyte
Precipitate
Solubility rules
Molecular equation and net ionic equations
Aqueous solution
Solution = homogenous mixture = solvent +
solute
Solute = what is being dissolved( ≥ 1)
Solvent= what solute is dissolved into
Aqueous solution(aq) = H2O =Created by
dissolving substances in water
Universal solvent
Electrolyte and nonelectrolyte
Electrolyte = dissociated in water to
form ions
-Strong electrolyte = completely
dissociate (NaCl, MgSO4, KI)
( Dissolve and Dissociate )
-Weak electrolyte= partially dissociate
-Non electrolyte = few ( or none) ions
exists
In summary, for an electrolyte solution, the key to conduct electricity is
to dissociated into its ionic form.
Hydration and Chemical equilibrium
Hydration, the process in
which an ion is surrounded
by water molecular
arranged in a specific
manner.
NaCl(s)
Na+ (aq) + Cl- (aq)
Dissolve and Dissociate
CH3COOH (aq)
CH3COO-(aq) + H+
Dissolve and Partially Dissociate
CH3OH(l) + H2O
Only Dissolve
CH3OH (aq)
Chemical equilibrium ( Dissolve
vs. Dissociate)
Equilibrium- nothing happens?
Equilibrium – reversible process
Questions
1. Which of the following diagrams best represents the
hydration of NaCl when dissolved in water? The Cl- ion
is larger in size than the Na+ ion.
2. Identify each of the following substances as a
strong electrolyte, weak electrolyte, or
nonelectrolyte: (a) KCl, (b) HNO3, (c) CH3COOH,
(d) C12H22O11 (e) H2O,
Precipitate and solubility
Precipitate is formed when an insoluble
compound is produced in a reaction.
If a compound is soluble in water (aq)
If it is insoluble, it will precipitate (s)
Or bubbles(g)
Metathesis or double-displacement reaction
Solubility Rules
For some compound’s solubility, it has no reason/ explanation as to why one
compound is soluble in water and one compound is not. Thus, solubility “rules”
were developed based on experience.
2 ways to use the rules:
• To determine if a compound is soluble or insoluble
• To determine when precipitation will form when two or more solvents
are mixed together (determine the formula of the products, determine
product phases(states)
Solubility Rules
Examples : Determine if K2S, CaSO4 and AgClO3 are soluble or not?
K2S K+, S2- (anything contains K+ is soluble, Li+, Na+, Rb+, Cs+)
soluble
CaSO4 Ca2+, SO42- (any sulfate of Ag+, Ca2+, Sr2+, Ba 2+, Hg22+, and Pb2+) insoluble
AgClO3 ( Any chlorates are soluble )
soluble
Solubility Rules
Examples : Determine two solvents are mixed, will the precipitate
form?
(NH4)2CO3 (aq) + CaCl2( aq)
?
(NH4)2CO3 (aq) + CaCl2( aq)
2NH4Cl + CaCO3
(NH4)2CO3 (aq) + CaCl2( aq)
2NH4Cl(aq) + CaCO3 (s)
How to remember the solubility rules
Rule 1: Alkali metal ion are soluble
How to remember the solubility rules
How to remember the solubility rules
Rule 1. Alkali metal ion are soluble
Rule 2. Bicarbonate(HCO3-) , Ammonium ions( NH4+), Nitrates(NO3-),
Chlorates (ClO3-), and Perchlorates(ClO4-) BANCh
Rule 3. Three Halides( Cl-, Br -, I-), except when they meet Ag+, Hg22+, Pb2+
How to remember the solubility rules
How to remember the solubility rules
Rule 1. Alkali metal ion are soluble
Rule 2. Bicarbonate(HCO3-) , Ammonium ions( NH4+), Nitrates(NO3-),
Chlorates (ClO3-), and Perchlorates(ClO4-) BANCh
Rule 3. Three Halides( Cl-, Br -, I-), except when they meet Ag+, Hg22+, Pb2+
Rule 4. All the sulfates salts are soluable except Ag+, Hg22+, Pb2+, Ca2+, Sr2+,
Ba2+
How to remember the solubility rules
How to remember the solubility rules
Rule 1. Alkali metal ion are soluble
Rule 2. Bicarbonate(HCO3-) , Ammonium ions( NH4+), Nitrates(NO3-),
Chlorates (ClO3-), and Perchlorates(ClO4-) BANCh
Rule 3. Three Halides( Cl-, Br -, I-), except when they meet Ag+, Hg22+,
Pb2+
All the sulfates salts are soluable except Ag+, Hg22+, Pb2+, Ca2+, Sr2+, Ba2+
Insoluble compound
Carbonate( CO32-), phosphates(PO43-), chromates( CrO42-), sulfides (S2-)
and Hydroxides (OH-)
Except compounds containing alkali metal, Ammonium ions (NH4+) and
the Ba2+ ion
Molecular equation and ionic equation
Molecular equation: Formulas of the compounds are
written as though all species existed as molecules or
whole units. It is useful for reagents identification.
Pb2+(aq) + 2NO3-(aq) + 2K+(aq) +2I-(aq)
PbI2(s) + 2K+(aq) +2NO3-(aq)
Ionic equation : what is really happened in the aqueous solution
Pb2+(aq) + 2I-(aq)
PbI2(s)
Net ionic equation : shows only the species that actually react in the
reaction
Molecular equation and ionic equation
BaCl2(aq) + ZnSO4(aq)
?
A+B+ C+ DStep 1: Write a balance molecular equation based ABCD rule and
solubility rule
BaCl2(aq) + ZnSO4(aq)
BaSO4(s) + ZnCl2(aq)
Step 2: Split apart compounds from ions (determine changes) and
write down all the ions in the solution.
Ba 2+, Cl-, Zn 2+, SO42Ba2+(aq) + 2Cl-(aq) + Zn2+ (aq)+ SO42-(aq)
BaSO4(s) + Zn2+ +2Cl-
Step 3: Get rid of repeated ion at the reaction side and product side
of equation
Ba2+(aq) + 2Cl-(aq) + Zn2+(aq) + SO42-(aq)
BaSO4(s) + Zn2+(aq) +2Cl-(aq)
Step 4: Check the charges and number of atoms blance in the net
ionic equation
Ba2+(aq) + SO42-(aq)
BaSO4(s)
Practice
1) Mg(NO3)2(aq) + 2NaOH(aq)
2) Na2S (aq) + ZnCl2 (aq)
Practice
1) Mg(NO3)2(aq) + 2NaOH(aq)
Mg(OH)2 (s) + 2NaNO3(aq)
Mg2+ (aq) + 2NO3- (aq) + 2Na+ (aq) + 2OH- (aq)
Mg2+ (aq) + 2OH- (aq)
Mg(OH)2(s)
2) Na2S (aq) + ZnCl2 (aq)
ZnS(s) + 2NaCl(aq)
2Na+(aq) + S2-(aq) + Zn2+(aq)+2Cl-(aq)
S2-(aq) + Zn2+(aq)
Mg(OH)2(s) + 2NO3- (aq) + 2Na+ (aq)
ZnS(s)
ZnS(s) + 2Na+(aq)+ 2Cl-(aq)
Overview
Solution = homogenous mixture = solvent + solute
Solute = what is being dissolved( ≥ 1)
Solvent= what solute is dissolved into
Electrolyte:
-Strong electrolyte = completely dissociate (NaCl,
MgSO4, KI)( Dissolve and Dissociate )
-Weak electrolyte= partially dissociate
-Non electrolyte = few ( or None) ions exists
Precipitate: is formed when an insoluble compound is
produced in a reaction.
Solubility rules
Molecular equation and net ionic equations