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CHAPTER 9
Water and
Solutions
9.1 Solutes,
Solvents, and Water
What is a solution?
Is vinegar a solution?
Is milk a solution?
Is marble a solution?
‹#›
9.1 Solutes, Solvents, and Water
A true solution is homogeneous on the molecular level
Solid copper sulfate
(CuSO4)
Copper sulfate solution
In solution the copper ions (Cu2+) dissociate from the sulfate ions (SO42–)
‹#›
9.1 Solutes, Solvents, and Water
All solutions contain one solvent
‹#›
9.1 Solutes, Solvents, and Water
All solutions contain one solvent
and at least one solute
dissolved: term used to describe when molecules of
solute are completely separated from each other and
dispersed into a solution.
‹#›
9.1 Solutes, Solvents, and Water
Special case of water
Most of your body is water!
Water is an important
solvent with many unusual
properties
‹#›
9.1 Solutes, Solvents, and Water
Special case of water
Water is a small, polar molecule
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9.1 Solutes, Solvents, and Water
Special case of water
Water is a small, polar molecule
There is a strong attraction
among water molecules due
to hydrogen bonding
‹#›
9.1 Solutes, Solvents, and Water
Special case of water
Hydrogen bonding leads to interesting properties in water
Substances are generally
denser in the solid phase
than in the liquid phase.
Water is different
Why ice floats in water
‹#›
9.1 Solutes, Solvents, and Water
Special case of water
Hydrogen bonding leads to interesting properties in water
Substances are generally
denser in the solid phase
than in the liquid phase.
Water is different
Why ice floats in water
‹#›
In ice, hydrogen bonds force
water molecules to align in a
crystal structure where
molecules are farther apart
than they are in a liquid.
9.1 Solutes, Solvents, and Water
Special case of water
Hydrogen bonding leads to interesting properties in water
Why ice floats in water
‹#›
9.1 Solutes, Solvents, and Water
Special case of water
Water
H2O
18 g/mole
Methane
CH4
16 g/mole
Boils at +100oC
Boils at –161oC
Why are the boiling points so different?
‹#›
9.1 Solutes, Solvents, and Water
Special case of water
Hydrogen bonding leads to interesting properties in water
Water
H2O
18 g/mole
polar
Boils at +100oC
‹#›
Methane
CH4
16 g/mole
nonpolar
Boils at –161oC
9.1 Solutes, Solvents, and Water
Special case of water
Hydrogen bonding leads to interesting properties in water
Water
H2O
18 g/mole
polar
Boils at +100oC
Hydrogen bonds keep water
molecules together, preventing them
from separating easily.
‹#›
Methane
CH4
16 g/mole
nonpolar
Boils at –161oC
Without these strong
intermolecular forces, methane
is a gas at room temperature
9.1 Solutes, Solvents, and Water
Special case of water
Why a drop of water doesn’t “lie flat”
on a hard surface:
H-bonds keep the water
molecules together
In reality water molecules are much, much smaller than on this drawing!
surface tension: a force acting to pull a liquid surface into
the smallest possible area.
‹#›
9.1 Solutes, Solvents, and Water
Special case of water
Hydrogen bonding leads to interesting properties in water
Surface tension can make
a paper clip float on water
‹#›
9.1 Solutes, Solvents, and Water
Water as a solvent
Water is often called the “universal solvent”
Dissolves ionic compounds
‹#›
Dissolves many
molecular compounds
9.1 Solutes, Solvents, and Water
Water as a solvent
Not chemically bonded
hydration: the process of molecules with any charge
separation to collect water molecules around them.
‹#›
9.1 Solutes, Solvents, and Water
Water as a solvent
A glucose molecule
has a total charge
of zero,
but it has regions of
positive and
negative charge
separation.
‹#›
Not chemically bonded
9.1 Solutes, Solvents, and Water
Are there different “kinds” of water?
Distilled water
Deionized water
Tap water
‹#›
9.1 Solutes, Solvents, and Water
Tap water contains dissolved salts and minerals.
Distilled water and deionized water have been
processed to remove dissolved salts and minerals.
Deionization is a specific
filtration process to remove
all ions.
Distillation boils water to steam which is
then condensed back to liquid water
‹#›
9.1 Solutes, Solvents, and Water
How do we know that tap water contains ions and
distilled water does not?
Light bulb goes off!
‹#›
9.1 Solutes, Solvents, and Water
Reactions in solids
Chemical reactions in solids do occur, but they are slow
It takes thousands of years
for limestone to become
marble, under heat and
pressure in the Earth
High density
Low mobility
‹#›
9.1 Solutes, Solvents, and Water
Reactions in gases
Chemical reactions in gases do occur, and happen quickly
Low density
High mobility
‹#›
9.1 Solutes, Solvents, and Water
Reactions in liquids
Chemical reactions in liquids occur easily
‹#›
High density
High mobility
9.1 Solutes, Solvents, and Water
Reactions in liquids
Life involves many complex chemical reactions that only
occur in aqueous solutions!
A step in the Krebs cycle – this is how energy is extracted from glucose
‹#›
9.1 Solutes, Solvents, and Water
Not everything dissolves in water. Why not?
‹#›
9.1 Solutes, Solvents, and Water
Not everything dissolves in water. Why not?
In general,
“like” dissolves
“like”
‹#›
Polar solvents dissolve polar solutes
Nonpolar solvents dissolve nonpolar solutes
9.1 Solutes, Solvents, and Water
Hexane can dissolve oil
paints because both are
nonpolar.
In general,
“like” dissolves
“like”
‹#›
Polar solvents dissolve polar solutes
Nonpolar solvents dissolve nonpolar solutes
9.1 Solutes, Solvents, and Water
Water is often called the “universal solvent”:
Dissolving
ionic salts
In general,
“like” dissolves “like”
‹#›
Dissolving
molecular
compounds
Polar solvents dissolve polar solutes
Nonpolar solvents dissolve nonpolar solutes
9.1 Solutes, Solvents, and Water