Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chapter 4
Aqueous Reactions and
Solution Stoichiometry
4.1
Properties of
Aqueous
Solutions
1) Solution
• Homogeneous mixtures of two or
more pure substances (solute(s)
dissolved in solvent)
– Solvent - substance present in the
greatest quantity
– Solute(s) - all other substances present
in lesser quantities
(recall that solutions in which water
is the solvent are called
aqueous solutions)
2) Water: the Universal Solvent
• How is a substance dissolved in water?
– Water is known as the “universal solvent” due to
the fact that more substances dissolve in water
than any other chemical (it has to do with the
high polarity of each H2O molecule)
• Polarity – physical property
of a substance which results
from an uneven distribution
of positive and negative
charge in a molecule or
chemical bond
• However, not all substances can dissolve in
water and those that do dissolve in water
dissolve to varying degrees:
– Soluble
• a substance which dissolves easily and completely
in water, forming an aqueous solution
– Slightly (or partially) Soluble
• a substance which only dissolves a tiny bit in
water leaving the majority of the substance behind
in its original state of matter
– Insoluble
• a substance that does not dissolve in water and
remains in its original state of matter separate
from the H2O molecules (no interaction)
Solubility: a visual
• The process of solvation:
– During the solvation process, the cations
and anions that make up a soluble ionic
solute become dissociated (or separated)
from one another; these ions are then
attracted to and surrounded by the water
(solvent) molecules
(see visual of this process on next slide)
NaCl
+
H2O
1
2
3
4
• These dissociated ions are free to
move throughout the solution
resulting in electrical conductivity
(movement of charged particles
through a medium)
3) Determining Solubility of Compounds in Water
• To know if an ionic compound is soluble or not,
you must consult the solubility rules
(see next slide)
Solubility Rules for Common Ionic Compounds in Water
Soluble Ionic Compounds
Nitrates, NO3Acetates, C2H3O2Chlorides, ClBromides, BrIodides, ISulfates, SO42Alkali metal cations
Ammonium, NH4+
Exceptions: these are insoluble w/ respective anions
none
none
Ag+, Hg22+ (2 Hg atoms), Pb2+
Ag+, Hg22+, Pb2+
Ag+, Hg22+, Pb2+
Ag+, Hg22+, Pb2+, Sr2+, Ba2+
none
none
Insoluble Ionic Compounds
Sulfides, S2Carbonates, CO32Phosphates, PO43Hydroxides, OH-
Exceptions: these are soluble w/ respective anions
alkali metal cations, NH4+, Ca2+, Sr2+, Ba2+
alkali metal cations, NH4+
alkali metal cations, NH4+
alkali metal cations, NH4+, Ca2+, Sr2+, Ba2+
Solubility Rules - Practice
• Are the following compounds soluble or
insoluble in water?
– Be(C2H3O2)2
– MgS
soluble
insoluble
– BaSO4 insoluble
– K3PO4 soluble
• In order to determine if covalent compounds are
soluble in water, you must determine the molecular
polarity of the compound (this is something you have not
yet learned how to do)*
• Acids are not explicitly listed in the rules because all the
acids that you will deal with are aqueous solutions (and
thus soluble)
– Substances that produce H+ ions when dissolved in
water (Arrhenius)
– Ex) HNO3  H+ + NO3–
• The only types of bases that you will see at this point will
be handled like ionic compounds
– Substances that produce OH− ions when dissolved in
water (Arrhenius)
– Ex) NaOH  Na+ + OH–
4) Strong vs. Weak Acids & Bases
• In the picture below, which acid is weak and which is strong?
• What is different about the contents in each of these beakers?
STRONG Acids & Bases
• These dissociate completely and exist as
100% ions in solution
Beaker (a) contains HCl
which dissociates 100% into
H+ and Cl– ions
Seven Strong Acids
MUST BE MEMORIZED!
• Hydrochloric (HCl)
• Hydrobromic (HBr)
• Hydroiodic (HI)
• Nitric (HNO3)
• Sulfuric (H2SO4)
• Chloric (HClO3)
• Perchloric (HClO4)
When dissolved
in water, they
dissociate 100%
into H+ ions and
their respective
anion.
Strong Bases
MUST BE MEMORIZED!
 Soluble hydroxide compounds
• Alkali metal hydroxides
• LiOH, NaOH, KOH, etc…
• Calcium hydroxide, Ca(OH)2
• Strontium hydroxide, Sr(OH)2
• Barium hydroxide, Ba(OH)2
When dissolved in water, they dissociate 100%
into their respective metal cation and OH–
WEAK Acids & Bases
• These only partially dissociate in solution
(only a few ions exist)
Beaker (b) contains HNO2
and it appears that only 1/5
of the HNO2 molecules have
dissociated into H+ and NO2–
5) Predicting Ions in Solution
• If a substance is soluble, then you can predict
what types of and how many ions present are in
the solution when each compound dissociates
– Ex) Ammonium sulfate
(NH4)2SO4  soluble
Dissociates into: 2 NH4+ ions
1 SO42- ion
– Ex) Phosphoric Acid
H3PO4  soluble
Dissociates into: 3 H+ ions
1 PO43- ion
6) Electrolytes
• An electrolyte is a substance which
possesses all of the following three qualities:
– is soluble water
– dissociates into ions when dissolved
– AND is a good conductor of electricity
• Aqueous solutions can be
classified into three
categories based on how
electrolytic they are:
Strong Electrolytes
• dissolves readily in water
(soluble)
• dissociates almost
completely into ions (~100%)
• good conductor of electricity
• Includes:
– all soluble ionic compounds
– all strong acids & bases
Weak Electrolytes
• Dissolves in water to a degree (slightly
soluble)
• dissociate only partially into ions (solution
exists mostly as molecules surrounded by
water = very, very few ions present in
solution)
• poor conductor of electricity
• Includes:
– slightly soluble ionic compounds
– weak acids & bases*
Nonelectrolytes
• does NOT dissociate into any
ions (dissolved substance
consists of intact molecules
surrounded by H2O)
• does not conduct electricity
• Includes:
– all insoluble ionic compounds
– most covalent compounds
(w/the exception of acids &
bases which are either strong
or weak)
Electrolytes: a visual
How to Classify Electrolytic Solutions
First determine if the substance is ionic, covalent, or
acid/base
• If IONIC, determine if it is soluble…
– If soluble = strong electrolyte
– If insoluble = nonelectrolyte
• If COVALENT and not an acid/base…
– These do not contain any ions and are
therefore considered nonelectrolytes
• If ACID/BASE, determine if it is a strong
acid/base…
– If strong acid or base = strong electrolyte
– if it is any other acid or base = weak electrolyte
Classify the following as:
strong, weak, or nonelectrolyte
compound
ionic, covalent, acid,
or base
soluble or insoluble
strong, weak, or
nonelectrolyte
1
CaCl2
ionic
soluble
strong
2
HNO3
acid
soluble
strong
3
Ag3PO4
ionic
insoluble
nonelectrolyte
4
HCHO2
acid
soluble
weak
5
KOH
ionic & base
soluble
strong
6
C2H5OH
covalent (not a base)
unknown*
nonelectrolyte
4.2
Precipitation
Rxns
Precipitation Reactions
• Precipitate (ppt.) – an insoluble solid formed
from the double replacement reaction of two
aqueous solutions
– In order to know if a precipitate will form…
• Predict the products of the double replacement
reaction (write the correct chemical formulas!)
• Use the solubility rules to determine if the
products are soluble (aq) or insoluble (s)
– If there is an insoluble (s) product then a
precipitate has formed and you must balance
the chemical equation
– If all products are aqueous, then no chemical
reaction (NR) has occurred
DEMO!!!
Will precipitates form?
• Solutions Used:
0.1 M KI
0.1 M CaCl2
0.1 M Pb(NO3)2
Net Ionic Equations & Spectator Ions
• Balanced chemical equations show chemical
formulas without considering the ionic
character of any of the substances
• However… recall that soluble ionic compounds
are strong electrolytes
• strong acids/bases & soluble ionic compounds
• This means they dissociate and are truly
present as ions in a sol’n
(which leads us to…)
• Complete Ionic Equation (CIE)
– rewrite a balanced chemical equation as the CIE to show
which compounds dissociate into ions (this is true only of
soluble, strong electrolytes in the aq state of matter)
• Spectator Ions
– ions present on both the reactant and product side of a
CIE which play no direct role in the chemical reaction
• Net Ionic Equation (NIE)
– after the CIE is written, cancel out all the spectator ions
so that the NIE includes only ions and compounds
directly involved in the chemical reaction
*When writing CIE and NIE, do NOT separate solid, liquid, or gaseous
reactants/products*
**When ALL reactants and products are AQUEOUS (no reaction), every ion
is a spectator ions (a CIE can be written but the NIE would be NR)**
4.4
OxidationReduction
Reactions
Single Replacement Rxns
• General Rxn Formula:
A + BC  AC + B
• The reactants:
– One reactant is a single element by itself
– The other reactant is an ionic compound
• The products:
– If the single element is a metal, it will replace
the cation in the ionic compound
– If the single element is a halogen gas, it will
replace the anion in the ionic compound
Oxidation-Reduction Rxns (aka: Redox)
• All single replacement
rxns can be classified as
Redox rxns (but not all
redox rxns are single
replacement)
•
Redox rxns occur
when electrons are
transferred between
reactants
• Oxidation occurs when
an atom, ion, or
molecule loses
electrons. (LEO)
• Reduction occurs
when an atom, ion, or
molecule gains
electrons. (GER)
* Both processes happen
simultaneously in a rxn
Activity Series of Metals
- Ease of Oxidation
• When a single replacement rxn occurs, the
metal that is alone will be oxidized.
• However, some metals are easier to oxidize
than others (they lose electrons more easily
than others, thus forming cations)
– Active Metals:
• metals at the top of the activity series are
more reactive and more easily oxidized
– Noble Metals:
• metals at the bottom of the activity series
which have very low reactivity
Activity Series of
Metals
In a single replacement
rxn:
----------------------------------------------------------------------
(1) a solid metal element
can be OXIDIZED by
any elements listed
below it in the activity
series
(2) Look to see if the
metal solid is ABOVE
the metal cation (in
the 2nd reactant)
 If yes, the rxn
does happen 
predict products
 If not, NR (b/c the
solid metal cannot
be oxidized)
Using the Activity Series
Examples
1) magnesium sulfate+ zinc metal
 NR
2) iron metal + copper (II) nitrate
Fe (s) + Cu(NO3)2 (aq)  Cu (s) + Fe(NO3)2
We can also write CIE & NIE!!! (only aqueous dissociate)
CIE:
Fe (s) + Cu2+ (aq) + 2 NO3– (aq)
 Cu (s) + Fe2+ (aq) + 2 NO3– (aq)
NIE:
Fe (s) + Cu2+ (aq)  Cu (s) + Fe2+ (aq)
Metals Reacting w/Acids
• Only metals listed ABOVE hydrogen in the
series are able to react with acids
• If the reaction does occur, H2 gas is
produced.
• Example #1:
2
___Ni (s) + ___HCl
(aq)  NiCl2(aq) + H2 (g)
 Ni is above H2, so the rxn occurs!
• Example #2:
___Cu (s) + ___HCl (aq)  NR
 Cu is below H2, so no rxn occurs!
Activity Series of Halogens:
ACTIVITY SERIES
• The idea is the same here…
OF HALOGENS:
– Fluorine is the most reactive
Fluorine
– Iodine is the least reactive
Chlorine
• Only a MORE reactive halogen can
Bromine
replace a LESS reactive one
Iodine
• In these single replacement rxns, the
single element (halogen gas) must be
listed ABOVE the halogen anion in the
2nd reactant for a rxn to occur
2
2
(aq) + ___Br2 (g)
• ___Cl2 + ___NaBr
(aq)  ___NaCl