Water, Polar molecules, and an
Intro to Solutions (p264 -280)
Lesson 1
Mr. Hoover, edited by Ms. Bacic
http://mrhoover.weebly.com/sch3uchemistry.html
UNIT: Solutions & Solubility
Chapters 6, 7 & 8
In this unit we discuss how and why
solutions form, how substances react in
solution using stoichiometry, the relevance
of water as a chemical, and its role in society
and technology.
 When we think of making a solution, the first
substance we think of is …
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Water: Essential for Life
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70% of the earth is covered in water
yet only 3 % of it is fresh water (drinkable)
& only 1 % of this is water is in a liquid state.
Canada has the most abundant supply of
fresh water in the world (7% of renewable H2O)
meaning, we have an incredibly important
responsibility to conserve and protect this
water supply.
WATER CYCLE
The water cycle is one method of natural
purification. Energy from the sun causes
water to evaporate, dissolved contaminates
are left behind as it rises. When the water
condenses it returns to earth as
precipitation.
 http://polaris.umuc.edu/cvu/envm/hydro/hydr
o.html
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Water that precipitates on
mountains can be
especially vital for the
survival of communities
living below.
For example . . .
The Himalayans
Retreating Mountain Glaciers
Pose Freshwater Shortage
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Himalayan glaciers are sometimes referred to as Earth's
"third pole" because they supply fresh water to
communities throughout Southeast Asia.
Roughly 210 million people live in the region, & another
1.3 billion people who live downstream depend on rivers
fed in part by glaciers and mountain snowpack.
Climate's influence on Himalayan glaciers is still a looming
concern for many scientists and governments, which
worry about how warming will affect the region's water
cycle. Norway is spending $12 million to expand
monitoring the glaciers & to help communities adapt
http://www.scientificamerican.com/article.cfm?id=retreating-mountain-glaciers-pose
Physical properties of
water
Pure water is colourless, odourless, and
tasteless.
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Whether or not an object sinks or floats
relates to its density compared to water.
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Pure water density = 1.0 g / mL
Water: Special Molecule !
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Water is unique in the fact that its
density decreases when it
becomes a solid due to the crystal
lattice it forms as a result of
hydrogen-bonding, causing ice to
float. This in turn acts a blanket
which prevents the water Thank you
H-bonding!
underneath from
freezing and
killing all life.
Hydrogen Bonds (FON)
Remember: Hydrogen bonding is…
 A strong dipole-dipole force between a positive
hydrogen atom of one molecule, and a highly
electronegative atom (N, O, F) in another
molecule.
Remember…
Hydrogen-bonding
is so FON!!!
Heat capacity is a measure of how much
heat it takes to heat one gram of a
substance 1 ° C.
 Water requires 4.18 J of heat to increase the
temperature of 1 gram 1 ° C.
 Its ability to absorb large amounts of energy
with a slow increase in temperature allows
for more moderate temperatures near bodies
of water, unlike deserts which freeze at night
and are burning hot during the day.
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Chemical Properties of
Water
Water is a polar molecule that consists of
oxygen and hydrogen molecules. The oxygen has
a larger electronegativity and so it creates a
partial – charge as it draws hydrogen’s electrons
closer to it.
 Draw this
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The large difference in charge allows for
Hydrogen bonding to occur between
molecules.
 This provides water with its unique surface
tension, high boiling point and ice that is less
dense. (see page 87 fig 7 for diagram)
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The polarity of water also allows water to
dissolve other polar molecules.
dissolves Like – polar dissolves polar and nonpolar dissolves non-polar
 Like
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Ionic substances disassociate into charged ions
when dissolved in water form electrolytic solutions
– conduct electricity
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Draw this
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http://catalog.flatworldknowledge.com/bookhub/4309?e=averill_1.0-ch04_s01
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Due to waters great ability to be a solvent it
can become contaminated easily.
What’s in Polluted Water?
 As
the amount of human activity increases
the amount of contaminants found in nearby
water also increase.
Contaminants are classified into three types.
i) contaminants that don’t dissolve in water
ii) biological contaminants (bacteria, viruses)
iii) soluble contaminants or chemicals
(pesticides,fertilizers & metal ions)
1. Physical Contaminants
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Objects that do not dissolve in water.
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Ex – oil, plastic, tree branches, leaves, peat,
silt.
2. Biological Contaminants
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Biological contaminants include bacteria
and viruses which may make the water
unsafe to consume.
3. Chemical Contaminants
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Chemicals that are soluble in water.
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Ex – metal ions, pesticides, fertilizers.
These are not visible but can lead to visible
effects such as an algae bloom
Solutions
Most substances contain water because it is
so good at dissolving other substances.
 WATER is AKA the “Universal Solvent”
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Technically it is not universal because water does
not dissolve non-polar substances.
Only non-polar can dissolve non-polar.
LIKE DISSOLVES LIKE substances
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All aqueous solutions use water as the
solvent and are transparent (clear).
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A solution is a homogeneous mixture of
substances composed of at least one solute
and one solvent that are uniform throughout
the sample. This can be in a liquid or gas
state.
Solute – A substance that is dissolved in
a solvent
 Solvent – The medium in which a solute is
dissolved.
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Properties of Aqueous
Solutions
Compounds can be classified as either
electrolytes or non-electrolytes.
 Electrolytes – solutes that form aqueous
solutions that conduct
electricity like salt water:
or NaCl in water.
Electrolytes are mostly highly
soluble ionic compounds
including bases like sodium hydroxide
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Substances that stay electronically neutral
when dissolved in water are called nonelectrolytes.
 Ex. glucose
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Non-electrolytes – solutes that form
aqueous solutions that do not conduct
electricity.
 Most molecular compounds
are non-electrolytes with the
exception of acids.
 C2H5OH - non-electrolyte
 HCl, HNO3 - electrolytes
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Solutions can also be classified as acids,
bases, or neutral. These will be covered
more in a latter chapter.
Review of bond types
Intermolecular
Force
Bonding Model
Ionic
- Involves electron transfer, forms cations
and anions
- Cations and anions are attracted to each
other
- IONIC BONDING
Review of bond types
Intermolecular Force Bonding Model
Polar Covalent
-
Involves unequal sharing of pairs of electrons
by atoms of two different atoms
Bonds can involve 1, 2, or 3 pairs of electrons.
- DIPOLE-DIPOLE FORCES
Review of bond types
Intermolecular Force Bonding Model
Covalent
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Involves equal sharing of pairs of electrons
Bonds can involve 1, 2, or 3 pairs of electrons.
- LONDON DISPERSION FORCES
Polar Molecules
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If a molecule contains
polar covalent bonds, the
entire molecule may have
a positive end and a
negative end.
This would then be
classified as a
polar molecule.
Polar molecules
Not all molecules that
contain polar covalent
bonds are polar molecules.
 This can be due to the
shape of the molecule.
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Guidelines for predicting polar
and nonpolar molecules
Type
Polar AB
HAx
Description
Examples
Diatomic compounds -2 elements
CO(g)
Any molecule with a single H
HCl(g)
AxOH Any molecule with a single OH at C2H5OH(l)
one end
OxAy Any molecule with an O at one end H2O(l), OCl2(g)
NxAy
Any molecule with an N at one end NH3(g), NF3(g)
Guidelines for predicting polar
and nonpolar molecules
Type
Non Ax
polar
Description
Examples
All elements
Cl2(g), N2(g)
CxAy Most carbon
compounds
(including organic
solvents, fats &
oils)
CO2(g), CH4(g)
Polar Vs. Non-Polar
NOTE: A simple way to determine whether a molecule is
polar is to ask whether it is symmetrical when drawn. If
it is, then it is likely non-polar.
Make sure to draw the lone pair electrons on one side!
POLAR
NON-POLAR
Intermolecular Forces
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Van der Waals forces
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Dipole-dipole force - attractive force between
polar molecules (permanent dipole forces)
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London dispersion force – temporarily induced
attractive forces between all molecules
ex. Graphite is made of sheets
of carbon atoms in a
hexagon shape, the sheets
slide past each other causing
graphite to be soft.
Hydrogen Bonds (FON)
The Third Intermolecular Force :
 A strong dipole-dipole force between a positive
hydrogen atom of one molecule, and a highly
electronegative atom (N, O, F) in another
molecule.
Remember…
Hydrogen-bonding
is so FON!!!
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All of the three intermolecular forces can be
interacting between molecules of the same
kind.
London Dispersion Forces
Hydrogen Bonding
Dipole –dipole forces
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The larger the polar component of the compound,
the more soluble it will be in water.
The larger the non-polar component of the
compound the more insoluble it will be in water and
the more soluble it is in non-polar solvents such as
oil.
Ex. methanol
very soluble
poisonous
ethanol
hexanol
soluble
regularly
consumed
slightly soluble
(affect of H-bonding
weakened by non-polar
part of the molecule)
HW: Questions –
Day 1: Read pg 266-268
pg 269 # 1acegi, 2acegi,3-6, 8
pg 271 # 2, 5, 6,
Day 2: Read 272 - 279
pg 276 figure 6- predict solubility,
pg 277 # 4,5, pg 279 # 9-12,
pg 280 # 2-4
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