Water and Aqueous Solutions
Intermolecular Forces
These are the attractions between
molecules not within the molecule
 These forces dictate what state the
molecular compound is at a given
temperature
 These forces are weaker than ionic and
covalent bonds

Types of Forces:
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Van der Waals- the weak attraction of
molecules for each other
1. Dispersion Force- the weakest of the
forces. This is caused by the motion of the
electron clouds of atoms as they pass each
other
2. Dipole-dipole forces- a little stronger
than dispersion forces, this is the attraction
between polar molecules.
What are polar molecules? These are
molecules that have polar bonds that do not
cancel out each other. They usually have lone
pairs on the molecule.
Polar bonds- the unequal sharing of
electrons between elements
3. Hydrogen bonding: This is the
strongest intermolecular force of the three.
A very strong attraction between H of
one molecule and either F, O, or N of
another molecule.
The Water Molecule:

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A highly polar molecule that is essential to
life
Held together by strong hydrogen bonding
Because of the hydrogen bonding, water
displays capillarity – the movement of
water up a tube against gravity, and has
surface tension- the inward pull of the
water molecules so that the surface area of
the liquid is minimized
Hydrogen bonding also allows water to:
- Have a low vapor pressure- the pressure
inside a closed container caused by the
evaporation and the condensation of
water
- Have a high boiling point
- Have a high heat of vaporization
- Have high specific heat capacity
Since H bonding is strong, it takes more
energy to break the bonds apart
Specific Heat Capacity
It takes 4.18 Joules (1 cal) to raise the
temperature of 1 g of water 1o C
 Water is a good medium for solar energy
 The air temperature around a large area
of water remains fairly constant due to
the ability of water to absorb and give off
the large amount of energy

Water Vapor and Ice
Heat of vaporization- the amount of
energy needed to convert 1 g of a
substance from a liquid to a gas at the
boiling point
 Due to hydrogen bonding, it takes 2.26 kJ
to convert 1 g of liquid water at 100o C
to 1 g steam at 100o C. The bonds hold
the molecules together, so it takes a lot of
energy to break those bonds

How much energy is needed to change
86.0 g of water at 100o C to 86.0 g of
steam at 100o C?
Equation: mass x heat of vaporization
86.0 g x 2.26 kJ/g
= 194 kJ
Likewise, when water condenses from
steam at 100o C to liquid at 100o C,
2.26 kJ is given off.
 This shows that the heat of vaporization
of water is equal to the heat of
condensation of water
 You can get a worse burn from steam
than from water at the same temperature
because of the energy absorbed by the
water to make the steam

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Molecules of nearly the same molecular
mass as water have lower boiling points
and melting points because they do not
have the hydrogen bonding that water
has.
Ice


Most liquids, when they become solids,
condense, so the volume decreases, thereby
increasing its density
This does not happen with water
As water cools, the density does increase
until it reaches 4o C. At this temperature,
there is a change in the structure of the
molecules where they form an open
structure that has a larger volume,
decreasing the density
This is why ice floats when added to
water.
 This allows the creatures in water to be
able to survive during winter

Heat of FusionThe heat that is absorbed when 1 g of
water changes from a solid to a liquid is
334 J/g. This is the amount of energy
needed to break the bonds that hold ice
together
How much energy in kJ is needed to
change 47.6 g of ice at 0o C to liquid
water at the same temperature?
mass x heat of fusion
47.6 g x 0.334 kJ/g
= 15.9 kJ
Aqueous Solutions:
Solutions- samples containing dissolved
substances. Aqueous solutions- water is the
solvent
Solvent- what the substance is dissolved in
Solute-the dissolved particles.
these can be ionic or molecular
Solutions are also called homogeneous mixtures
Ionic compounds and polar covalent molecules
dissolve easily in water
Nonpolar covalent molecules do not dissolve in
water
During Solvation- (the process of dissolving
a substance)
the negative and positive ions are
separated by the solvent molecules
sometimes the ionic bonding is so strong
that the solute cannot come between
them, and the substance is insoluble
Oil and Gasoline are nonpolar, so they
cannot be dissolved in water“Like dissolves Like”
Electrolytes and Nonelectrolytes:
Electrolytes- these conduct electric
current in aqueous solution and when
melted
those that are insoluble only conduct
current when melted
Examples: NaCl, CuSO4 , NaOH
Electrolytes can be weak or strong-
Weak electrolytes- only a portion of the
solute exist as ions
Strong electrolytes- almost all the solute
exists as ions
Nonelectrolytes- do not conduct current
in aqueous solution or when melted
Examples: cane sugar, rubbing alcohol
Water of Hydration:
Some compounds contain water within
their crystal structure- the water within is
called the water of hydration.
The compound is called a hydrate
The water can be lost if the compound is
heated above 100o C- WHY?
A hydrate can effloresce if its vapor
pressure is higher than that of water, the
hydrate loses the water of hydration
Hygroscopic- compounds that can remove
moisture from the air.
These are used as desiccants or drying
agents
silica gels are put in purses or shoes
Deliquescent compounds can remove
enough water from the air so that they
become solutions
Naming- You name the compound and then
add the hydrate with a prefix to tell how
many waters are in the crystal
Ex: CuSO4 • 5H2O:
Copper (II) sulfate pentahydrate
Heterogeneous Aqueous Systems:
Suspensions- mixtures where the particles
can settle out
-clay in water
Colloids- particles are smaller than those in
suspensions, but larger than those in solution
Many examples- whipped cream, milk, fog,
dust in air
Tyndall Effect- when you shine a light
through a colloid and the light scattersdon’t use high beams in the fog
Brownian Motion- the random chaotic
motion of the particles in a colloid caused
by the collision of water molecules with
the particles
Emulsion- a colloidal dispersion of a liquid
in a liquid. An emulsifying agent must be
used to allow the liquids to mix.
Example- oil and water don’t mix, but
when you add soap, the emulsion occurs