UNIT 4: Solutions and Solubility
Chapter 8: Solutions and Their Properties
Chapter 9: Reactions in Aqueous
Solutions
How are qualitative analysis and quantitative
analysis used to describe the composition of a
solution, and how do humans use and affect the
world’s water supply?
Chapter 10: Acids and Bases
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Chapter 9: Reactions in Aqueous Solutions
All forms of life have one thing
in common – water. Water’s
ability to dissolve many
different compounds enables it
to carry the nutrients required
by the vast range of life forms
on Earth. However, water can
also dissolve and carry harmful
compounds, both natural
substances and human-made
pollutants.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1
9.1 Net Ionic Equations and
Qualitative Analysis
The reaction shown here is a double displacement reaction
with a spectacular colour change. In water, ionic substances
dissociate into their component ions. Non-reacting ions in an
aqueous solution are called spectator ions.
Note that water is
not a reactant in the
chemical equation.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1
Writing Ionic Equations
In an ionic equation, the formulas of soluble ionic
compounds are replaced with the formulas of the ions that
these compounds form in water. The following equation:
2AgNO3(aq) + Na2CrO4(aq)  Ag2CrO4(s) + 2NaNO3(aq)
becomes:
2Ag+(aq) + 2NO3-(aq) + 2Na+(aq) + CrO42-(aq) 
Ag2CrO4(s) + 2Na+(aq) + 2NO3-(aq)
when the formulas for ionic substances are written in
dissociated form.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1
Writing Net Ionic Equations
Spectator ions will appear on both sides of the equation
and can be canceled to obtain the net ionic equation. This
equation shows only the ions that react.
2Ag+(aq) + CrO42-(aq)  Ag2CrO4(s)
It is convenient to use this form of the equation since the
source of the silver and chromate ions does not matter.
Changing the spectator ions does not change the reaction.
Spectators are present at
a sporting event but do not
take part in the event, just
as spectator ions are
present in a reaction but
do not take part in it.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1
Rules for Writing a Net Ionic Equation
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1
Rules for Writing a Net Ionic Equation
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Qualitative Analysis
Qualitative analysis identifies elements, ions, or
compounds in a sample. To identify certain ions, you
can observe the:
• colour in a flame test
• colour of a solution
• formation of a precipitate
Fireworks are a spectacular
demonstration of the different
colours of light that are given
off by metal ions when they
are heated.
Section 9.1
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1
Flame Tests
Since many metal ions produce a distinct colour when
heated, a flame test (described below) can help identify
metal ions.
A Bunsen burner and a clean wire loop are used to test an
aqueous solution (dip the loop) or a solid (moisten the loop
with HCl(aq)). The substance is placed on the loop and
then into the flame. Electrons in
the atoms of the sample absorb
energy from the flame, and some
of the energy as visible light.
These photographs show flame tests of
strontium and copper. Notice that the
colour of the copper flame is greener
than a typical Bunsen burner flame.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Flame Tests
Section 9.1
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1
Colours of Ions in Solution
Aqueous solutions of ionic compounds of certain cations
and anions have characteristic colours.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Formation of a Precipitate
Another way to identify an unknown ion in
a solution is to add a known reactant to the
solution and observe whether or not a
precipitate forms. The solubility guidelines
can be used to infer which ion must have
been present in the unknown solution. This
can be done multiple times to the same
solution to further identify ions in the
filtrate.
Section 9.1
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Formation of a Precipitate
Section 9.1
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.1 Review
Section 9.1
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.2
9.2 Solution Stoichiometry
Solution stoichiometry is often used in quantitative
analysis, which involves determining a quantity (how
much) of a substance is present in a sample.
In solution stoichiometry, known volumes and
concentrations of reactants or products are used to
determine the volumes, concentrations, or masses of other
reactants or products.
Accurate measurement is
important in both cooking
and chemistry. A cake
made from improperly
measured ingredients may
not look good and may not
taste good either!
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Rules for Solving Solution
Stoichiometry Problems
Section 9.2
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.2
Solution Stoichiometry
Problem Solving
Example
Given:
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Volume of AgNO3 solution = 100 mL
Mass of dried Ag(s) precipitate = 1.65 g
What is the molar concentration of silver nitrate solution?
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.2
Solution Stoichiometry Problem Solving
1. Calculate the amount in moles of Ag(s):
n(Ag) = 1.65 g ×
1 mol
= 0.015 296 mol
107.87 g
2. Use moles of Ag to calculate moles of AgNO3:
n =AgNO3 = 2 mol AgNO3 × 0.0015 296 mol Ag
2 mol
= 0.015296 mol AgNO3
3. Calculate the concentration of AgNO3:
c = 0.015 296 mol = 0.153 mol/L
0.100 L
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.2
Limiting Reactant Problems
The limiting reactant is usually the one that is the most
expensive. This is one way to keep the costs in industrial
chemical processes as low as possible.
These calculations are much like those in Chapter 7. The
amount in moles of a solution is determined using n = c × V.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.2 Review
Section 9.2
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
9.3 Water Quality
The figure below illustrates the fact that a very small amount
(0.01%) of Earth’s water, found in lakes and rivers as surface
water, is available for safe human use. The salt water in the
oceans makes up 97.5% of the total amount of water, and
most of the fresh water is unavailable in ground water
(0.74%) far below Earth’s surface or is frozen in polar ice
caps (1.75%).
Very little of the water on
Earth is fresh water, and
very little fresh water is
available for people to drink.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Harmful Substances
Water quality is affected by:
• naturally occurring substances, some of which are
harmful
• pollutants that originate from human activities
• water treatment standards
The quality of any water
depends on factors that are not
always immediately visible.
Section 9.3
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Naturally Occurring Harmful Substances
Ionic Compounds Containing Arsenic
• found in ground water beneath river deltas; more serious
in countries such as Bangladesh
• most ground water in Canada has less than 5 ppb,
considered to be the safe level
• long-term exposure to dangerous levels of these
compounds may lead to cancer and diabetes
Fluoride Ions
• less than 1 ppb is considered safe and actually
beneficial to strengthen tooth enamel
Fluoride ions prevent tooth
decay, but too much fluoride can
cause brown stains on teeth.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Naturally Occurring Harmful Substances
Calcium and Magnesium Ions
• high levels of calcium and magnesium ions make the
water hard, which leads to formation of insoluble soap
scum as well as a buildup of lime (calcium carbonate)
deposits in pipes and appliances
Many of the rocks in
southern Ontario
are limestone, which
makes most of the
water in this region
hard.
The lime scale in this
water pipe was caused
by hard water.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Pollutants from Human Activity
Two types:
• Point Source of Pollution: a single source with a
specific location
Example: wrecked tanker leaking oil
• Non-point Source of Pollution: no easily defined
location and may involve many substances spread over
large areas
Example: fertilizers used on farms
(A) Point source of pollution: Waste
water from a factory can quickly
pollute a body of water.
(B) Non-point source of pollution: Runoff from farms can carry fertilizer and
pesticides into nearby waterways.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Pollutants from Human Activity
Lead Compounds
The Ontario government introduced the Cosmetic
Pesticide Act in 2009 to protect the environment by
lowering or banning the use of harmful garden and lawn
pesticides. Despite these initiatives, pollutants such as
lead, mercury, nitrates, and phosphates are still a major
problem.
Lead is released by industrial processes such as ore
smelting, car battery production, and plastics production.
While environmental lead pollution has decreased
significantly, exposure is still occurring and can lead to
kidney failure, nerve damage, and brain disorders.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Pollutants from Human Activity
Mercury Compounds
Much of the mercury deposited in the Great Lakes comes
from emissions from coal-fired power plants, gold mines,
cement plants, and smelters.
Mercury is highly toxic; it affects the central nervous
system, producing tremors, irritability, numbness, and
tunnel vision.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Pollutants from Human Activity
Nitrate and Phosphate Ions
The source of these ions comes mainly from livestock
waste and fertilizer use. These ions may leach into lakes
and rivers, where they promote plant and algal growth
(blooms). The bacteria that decompose this algal growth
absorb the available oxygen, leaving the fish populations
starved of oxygen.
Nitrate and phosphate
pollution can cause
excessive plant growth
in lakes and rivers.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Pollutants from Human Activity
Although algal blooms
appear to help plant
growth at first, the
overall environmental
effect is negative
because of the loss of
both plant and animal
life.
Section 9.3
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Pollutants from Human Activity
Infants less than three months old are susceptible to high
concentrations of nitrate ions in the water. Nitrate ions are
converted to nitrite ions in an infant’s digestive tract.
These ions bond to the hemoglobin, leading to a condition
known as blue-baby syndrome.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Pollutants from Human Activity
Airborne Pollution
Non-metallic oxides such as carbon dioxide, sulfur
dioxide, and nitrogen oxide gases dissolve in rainwater
and contribute to acid rain. Sources of these pollutants
include motor vehicles, refineries, and many factories.
Acid rain leaches aluminum ions into ground water and
surface water, which can harm
aquatic life considerably.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Pollutants from Human Activity
Plastic Leachates
Water bottles and other hard plastic containers contain
polycarbonates. Polycarbonates are made using the chemical
bisphenol A (BPA). This substance can leach into the liquid
inside the plastic container. Recently BPA has been linked to
breast cancer, heart disease, and other biological changes such
as those caused by the hormone estrogen.
Although banned from baby bottles, BPA is
still found in food containers and continues
to leach into the environment from landfills.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Water Quality and Drinking
Water Standards
In North America, various treatment plants ensure that
our drinking water is clear, colourless, tasteless, and
odourless and is free of disease-causing organisms and
unsafe levels of toxic compounds.
Ontario has maximum allowable concentration (MAC)
standards for selected ions and compounds in drinking
water.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Maximum Concentrations of Selected Ions
and Compounds in Ontario’s Drinking Water
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3
Maximum Concentrations of Selected Ions
and Compounds in Ontario’s Drinking Water
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.3 Review
Section 9.3
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
9.4 Water Treatment
Serious consequences result when water is polluted and
then not treated properly to make it safe to drink. Here are
a few examples:
• May 2000: A well for the town of Walkerton was
contaminated by run-off from a nearby farm. This runoff contained E. coli bacteria from animal manure and
was not tested or processed properly. Seven people
died, and thousands became seriously ill.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Polluted Water
• 1962: Reed International in Dryden, Ontario began using
mercury in a process to make bleaching chemicals for its
pulp and paper plant. The mercury waste water was
dumped into the river. Mercury compounds accumulated in
local fish, which were eaten by local residents. Residents
became sick with mercury poisoning, and, to this day,
newborns still show clear signs of mercury poisoning.
Between 1962 and 1970, Reed
International dumped over 9000 kg
of mercury into the WabigoonEnglish River system.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Water Treatment: Temporary Hardness
Hard water contains dissolved calcium (and magnesium)
carbonates. CaCO3(s) + H2O(ℓ) + CO2(aq) + Ca(HCO3)2(aq)
Calcium hydrogen carbonate Ca(HCO3)2(aq) and the
comparable magnesium compound are the main causes of
temporary hardness.
Boiling removes carbon dioxide from the solution, so it is not
available to react to make calcium hydrogen
carbonate. However, the calcium carbonate
precipitates out of the solution and deposits
on the heating appliance. Deposits of calcium carbonate
and magnesium carbonate on
water-heating elements can
reduce the heater’s efficiency.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Water Treatment: Permanent Hardness
Permanent water hardness is caused by dissolved calcium
(and magnesium) sulfate. This hardness cannot be removed by
boiling but must be treated by chemical methods.
One way is to add sodium carbonate, Na2CO3•10H2O (washing
soda) as a water softener. This precipitates the calcium (and
magnesium) carbonates out of solution.
CaSO4(aq) + Na2CO3(s)  CaCO3(s) + Na2SO4(aq)
This treatment makes the water basic. Use of an ion-exchange
water softener avoids this problem.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Water Treatment:
Ion-Exchange Water Softeners
Water softened by
an ion-exchange
softener contains a
high concentration
of sodium ions.
People on a lowsodium diet should
avoid drinking water
from a sodium ion
water softener.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Water Treatment: Desalination
The process of obtaining fresh water from salt water is called
desalination. Once it is safe to drink, the water is called
potable water.
Desalination plants are commonly
used in the Middle East where oil
is a cheap fuel used to heat the
ocean water. The salt-free water
vapour is condensed and collected.
The Jubail desalination plant, on the Arabian Gulf
in Saudi Arabia, is the largest desalination plant in
the world. Some of the energy that is needed to
boil the water comes from waste heat from an
adjacent electrical power plant.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Water Treatment: Reverse Osmosis
Reverse osmosis is a more energy-efficient method for
making potable water.
• Osmosis is the tendency of a solvent to move through a
semi-permeable membrane to make the concentrations
of solutes on both sides of the membrane equal.
• Therefore, water will flow from the more dilute side
into the more concentrated side.
• In reverse osmosis, high pressure is applied to the more
concentrated side to force water through the membrane
in the reverse-of-the-normal direction.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Water Treatment Reverse Osmosis
Desalination Plants
Large reverse osmosis desalination plants are built in coastal
areas. The largest in North America is in Tampa Bay, Florida.
It produces 100 million litres of potable water daily.
High pressure forces water across a
semi-permeable membrane inside
these vessels. The water that passes
through the membranes is completely
free of salt and other ions.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Water Supply Treatment
As shown in the graph, life expectancy has increased
dramatically since around 1800. Many health scientists have
concluded that this is due mostly to the widespread
improvement in the quality of water supplies around that time.
Life expectancy in
North America has
increased steadily
since 1800, partly
because of
improvements in
water treatment.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Municipal Water Treatment
Municipalities use
a combination of
physical and
chemical
processes to
purify water.
Section 9.4
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Waste-Water Treatment
The goal of waste-water treatment is to remove solids,
chemicals, and dangerous bacteria from sewage. The water
can then be released into the environment.
Waste-water treatment
plants remove possible
pollutants from sewage
so that those pollutants
cannot enter and harm
the environment.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4
Stages in Waste-Water Treatment
• Primary Treatment in holding tanks removes solid materials
by sedimentation and by skimming scum from the surface
of the water. The addition of calcium hydroxide and
aluminum sulfate promotes formation of aluminum
hydroxide precipitate.
• Secondary Treatment uses natural micro-organisms that feed
on organic matter in the sewage. These bacteria convert
organic material into carbon dioxide, water, and nitrogen
compounds.
• Tertiary Treatment involves chemical precipitation of
nitrogen, phosphorus, and organic compounds.
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Stages in Waste-Water Treatment
Section 9.4
UNIT 4 Chapter 9: Reactions in Aqueous Solutions
Section 9.4 Review
Section 9.4