Water and Aquaous System: Chemistry of Water

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Sharp Tutor Tue, Jan 25, 2022 01:06 PM UTC

We will discuss the properties of water-related to its chemistry. Water is a substance composed of the chemical elements hydrogen and oxygen and exists in gaseous, liquid, and solid states. It is one of the most plentiful and essential compounds.

1. 15.1 Water and Its Properties >
Chapter 15
Water and Aqueous Systems
15.1 Water and Its Properties
15.2 Homogeneous Aqueous
Systems
15.3 Heterogeneous Aqueous
Systems
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2. 15.1 Water and Its Properties > CHEMISTRY & YOU
What properties of water make it
essential to life on Earth?
Water covers about
three quarters of
Earth’s surface. All
known life forms are
made mostly of
water.
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3. 15.1 Water and Its Properties > Water in the Liquid State
Water in the Liquid State
What factor causes the high surface
tension, low vapor pressure, and high
boiling point of water?
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4. 15.1 Water and Its Properties > Water in the Liquid State
Water, H2O, is a simple molecule
consisting of three atoms.
• The oxygen atom forms a covalent bond
with each of the hydrogen atoms.
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5. 15.1 Water and Its Properties > Water in the Liquid State
Water, H2O, is a simple molecule
consisting of three atoms.
• The oxygen atom forms a covalent bond
with each of the hydrogen atoms.
• Oxygen has a greater electronegativity
than hydrogen, so the oxygen atom attracts
the electron pair of the covalent O—H bond
to a greater extent than the hydrogen atom.
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6. 15.1 Water and Its Properties > Water in the Liquid State
Water, H2O, is a simple molecule
consisting of three atoms.
• The oxygen atom forms a covalent bond
with each of the hydrogen atoms.
• Oxygen has a greater electronegativity
than hydrogen, so the oxygen atom attracts
the electron pair of the covalent O—H bond
to a greater extent than the hydrogen atom.
• Thus, the O—H bond is highly polar.
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7. 15.1 Water and Its Properties > Water in the Liquid State
• The oxygen δ– δ–
atom acquires a
partial negative
charge (δ–). δ+ δ+
Polar bonds Molecule has net polarity
δ– δ–
δ+ δ+
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8. 15.1 Water and Its Properties > Water in the Liquid State
• The oxygen δ– δ–
atom acquires a
partial negative
charge (δ–). δ+ δ+
Polar bonds Molecule has net polarity
• The less δ– δ–
electronegative
hydrogen atoms δ+ δ+
acquire partial
positive charges
(δ+).
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9. 15.1 Water and Its Properties > Water in the Liquid State
How do the polarities of the two O—H
bonds affect the polarity of the molecule?
δ– δ–
δ+ δ+
Polar bonds Molecule has net polarity
δ– δ–
δ+ δ+
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10. 15.1 Water and Its Properties > Water in the Liquid State
How do the polarities of the two O—H
bonds affect the polarity of the molecule?
δ– δ–
• The molecule
has a bent
shape.
δ+ δ+
Polar bonds Molecule has net polarity
δ– δ–
δ+ δ+
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11. 15.1 Water and Its Properties > Water in the Liquid State
How do the polarities of the two O—H
bonds affect the polarity of the molecule?
δ– δ–
• The molecule
has a bent
shape.
δ+
• The two O—H δ+
bond polarities Polar bonds Molecule has net polarity
δ– δ–
do not cancel.
δ+ δ+
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12. 15.1 Water and Its Properties > Water in the Liquid State
How do the polarities of the two O—H
bonds affect the polarity of the molecule?
δ– δ–
• The molecule
has a bent
shape.
δ+
• The two O—H δ+
bond polarities Polar bonds Molecule has net polarity
δ– δ–
do not cancel.
• The water
molecule as a δ+ δ+
whole is polar.
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13. 15.1 Water and Its Properties > Water in the Liquid State
In general, polar molecules are attracted
to one another by dipole interactions.
• The negative end of
δ+ one molecule attracts
the positive end of
another molecule.
δ–
δ+
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14. 15.1 Water and Its Properties > Water in the Liquid State
However, in water, this attraction results
in hydrogen bonding.
• Hydrogen bonds are attractive forces that
arise when a hydrogen atom is covalently
bonded to a very Hydrogen
bond
electronegative
atom and also
weakly bonded to an
unshared electron
pair of another
electronegative
Liquid water
atom.
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15. 15.1 Water and Its Properties > Water in the Liquid State
Many unique and important
properties of water—including
its high surface tension, low
vapor pressure, and high
boiling point—result from
hydrogen bonding.
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16. 15.1 Water and Its Properties > Water in the Liquid State
Surface Tension
Have you ever noticed that water forms
nearly spherical droplets on a leaf?
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17. 15.1 Water and Its Properties > Water in the Liquid State
Surface Tension
• The water molecules within the body of the liquid
form hydrogen bonds with the other molecules that
surround them on all sides.
• The attractive forces on each of
these molecules are balanced.
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18. 15.1 Water and Its Properties > Water in the Liquid State
Surface Tension
• The water molecules within the body of the liquid
form hydrogen bonds with the other molecules that
surround them on all sides.
• The attractive forces on each of
these molecules are balanced.
• Water molecules at the surface
of the liquid experience an
unbalanced attraction.
• As a result, water molecules at
the surface tend to be drawn
inward.
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19. 15.1 Water and Its Properties > Water in the Liquid State
Surface Tension
The inward force, or pull, that tends to
minimize the surface area of a liquid is
called surface tension.
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20. 15.1 Water and Its Properties > Water in the Liquid State
Surface Tension
The inward force, or pull, that tends to
minimize the surface area of a liquid is
called surface tension.
• All liquids have a surface tension, but
water’s surface tension is higher than most.
• The surface tension of water tends to hold a
drop of liquid in a spherical shape.
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21. 15.1 Water and Its Properties > Water in the Liquid State
Surface Tension
It is possible to decrease the surface
tension of water by adding a surfactant.
• A surfactant is any substance that
interferes with the hydrogen bonding
between water molecules and thereby
reduces surface tension.
• Soaps and detergents are surfactants.
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22. 15.1 Water and Its Properties > Water in the Liquid State
Vapor Pressure
Hydrogen bonding between water
molecules also explains water’s unusually
low vapor pressure.
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23. 15.1 Water and Its Properties > Water in the Liquid State
Vapor Pressure
Hydrogen bonding between water
molecules also explains water’s unusually
low vapor pressure.
• An extensive network of hydrogen bonds holds
the molecules in liquid water to one another.
• These hydrogen bonds must be broken before
water changes from the liquid to the vapor
state, so the tendency of these molecules to
escape is low and evaporation is slow.
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24. 15.1 Water and Its Properties > Water in the Liquid State
Boiling Point
Molecular compounds of low molecular
mass are usually gases or liquids with
low boiling points at normal atmospheric
pressure.
• Ammonia (NH3) has a molar mass of
17.0 g/mol and boils at about –33˚C.
• Water has a molar mass of 18.0 g/mol,
but it has a boiling point of 100˚C.
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25. 15.1 Water and Its Properties > Water in the Liquid State
Boiling Point
The difference between the boiling points
of ammonia and water is due to hydrogen
bonding, which is more extensive in water
than in ammonia.
• It takes much more heat to disrupt the
attractions between water molecules
than those between ammonia molecules.
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26. 15.1 Water and Its Properties >
Some insects are able to walk across
water. How do the properties of water
explain their ability?
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27. 15.1 Water and Its Properties >
Some insects are able to walk across
water. How do the properties of water
explain their ability?
The surface tension of water is
relatively high. As long as the forces
holding the surface water molecules
together are stronger than the forces
exerted down on the water by the
insect, the insect will not sink.
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28. 15.1 Water and Its Properties > Water in the Solid State
Water in the Solid State
How can you describe the
structure of ice?
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29. 15.1 Water and Its Properties > Water in the Solid State
Ice cubes float in your glass of iced tea
because solid water has a lower density
than liquid water.
• This situation is not usual for liquids.
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30. 15.1 Water and Its Properties > Water in the Solid State
As water begins to cool, it behaves
initially like a typical liquid.
• It contracts slightly, Density of Liquid Water and Ice
and its density Temperature (˚C) Density (g/cm3)
gradually increases. 100 (liquid water) 0.9584
50 0.9881
• When the 25 0.9971
temperature of the 10 0.9997
water falls below 4 1.0000
4˚C, the density of 0 (liquid water) 0.9998
0 (ice) 0.9168
water actually starts
to decrease.
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31. 15.1 Water and Its Properties > Water in the Solid State
Below 4˚C, water no longer behaves like
a typical liquid.
• Ice, which forms at Density of Liquid Water and Ice
0˚C, has about a Temperature (˚C) Density (g/cm3)
10% lower density 100 (liquid water) 0.9584
than water at 0˚C. 50 0.9881
25 0.9971
• Ice is one of only a 10 0.9997
few solids that 4 1.0000
0 (liquid water) 0.9998
floats in its own
0 (ice) 0.9168
liquid.
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33. 15.1 Water and Its Properties > Water in the Solid State
Why is ice less dense than liquid water?
The structure of ice is a regular open
framework of water molecules in a
hexagonal arrangement.
The hexagonal
symmetry of a
snowflake reflects the
structure of the ice
crystal.
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34. 15.1 Water and Its Properties > Water in the Solid State
The unique properties of ice are a result
of hydrogen bonding.
• Extensive hydrogen
Hydrogen bonding in ice holds
bond the water molecules
farther apart in a
more ordered
arrangement than in
liquid water.
Ice
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35. 15.1 Water and Its Properties > Water in the Solid State
The fact that ice floats has important
consequences for all organisms.
• The liquid water at the bottom of an
otherwise frozen body of water is warmer
than 0˚C, so fish and other aquatic life are
better able to survive.
• If ice were denser than liquid water,
bodies of water would tend to freeze solid
during the winter months, destroying
many types of organisms.
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36. 15.1 Water and Its Properties > CHEMISTRY & YOU
What properties of water that result from hydrogen
bonding make it essential to life on Earth?
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37. 15.1 Water and Its Properties > CHEMISTRY & YOU
What properties of water that result from
hydrogen bonding make it essential to life
on Earth?
• The low vapor pressure of water keeps the
liquid water in all of Earth’s lakes and oceans
from evaporating rapidly.
• If water did not have such a high boiling point,
it would be a vapor at the usual temperatures
found on Earth.
• The fact that ice floats allows fish and other
aquatic life to survive the winter months.
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38. 15.1 Water and Its Properties >
In ice, how many hydrogen bonds can
be formed between one hydrogen atom
of a water molecule and the oxygen in
surrounding water molecules?
A. 0
B. 1
C. 2
D. 3
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39. 15.1 Water and Its Properties >
In ice, how many hydrogen bonds can
be formed between one hydrogen atom
of a water molecule and the oxygen in
surrounding water molecules?
A. 0
B. 1
C. 2
D. 3
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40. 15.1 Water and Its Properties > Key Concepts
Many unique and important
properties of water—including its high
surface tension, low vapor pressure,
and high boiling point—result from
hydrogen bonding.
The structure of ice is a regular open
framework of water molecules in a
hexagonal arrangement.
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41. 15.1 Water and Its Properties > Glossary Terms
• surface tension: an inward force that
tends to minimize the surface area of a
liquid; it causes the surface to behave
as if it were a thin skin
• surfactant: any substance that
interferes with the hydrogen bonding
between water molecules and thereby
reduces surface tension; soaps and
detergents are surfactants
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42. 15.1 Water and Its Properties > BIG IDEA
Bonding and Interactions
• Water molecules are held together through
hydrogen bonds.
• The hydrogen bonding interactions between
water molecules account for the unique
properties of water, including its high surface
tension, low vapor pressure, and high boiling
point.
• Hydrogen bonding also accounts for the fact
that ice is less dense than liquid water.
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