Water
Water Overview
 All living things need
water more than any other
substance
 Most cells are surrounded
by water, and cells
themselves are about 7095% water (we are bags of
meat and water)
 Water is the only substance
on earth that is found
naturally in solid, liquid,
and gas forms
Water and Solutions
 Water molecules are polar,
which means they have
oppositely charged areas (there
is an unequal distribution of
charges, so the oxygen is
negative, and the hydrogen is
positive) – like a magnet.
 When one water molecule
comes close to the oppositely
charged region of another water
molecule, it creates a weak
attraction called a hydrogen
bond
 A hydrogen bond is an attractive
force between a hydrogen atom
and an electronegative atom
Properties of Water
• There are four main
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properties of water that
facilitate an environment
for life on our planet:
Cohesiveness
Ability to moderate
temperature
Expansion upon freezing
Versatility as a solvent
Properties of Water cont.
(hydrogen bonds)
 Hydrogen bonds are
what is responsible for
cohesion (when two like
molecules attract)
 Adhesion is when two
unlike molecules attract
(water and detergent or
water and glass)
Moderation of Temperature
 Water can moderate air
temperature by
absorbing heat from air
that’s warmer, and
releasing stored heat to
air that is cooler.
Temp cont.
 The specific heat of a
substance is the amount of
heat that must be absorbed
or lost for 1 gram of that
substance to change its
temperature by 1ºC
 Water’s high specific heat
minimizes temperature
fluctuations to within
limits that permit life
 Heat is absorbed when
hydrogen bonds break
 Heat is released when
hydrogen bonds form
Expansion upon freezing
 Ice floats in liquid water
because hydrogen bonds
in ice are more “ordered,”
making ice less dense
 If ice sank, all bodies of
water would eventually
freeze solid, making life
impossible on Earth
Solvent
 A hydrophilic
substance is one that
has an affinity for
water (hydro is greek
for water, philios,
loving).
 A hydrophobic
substance is one that
does not have an
affinity for water
(phobic is greek for
fearing).
Water cont.
 A mixture is a
combination of two or
more substances where
each retains its
individual characteristics
(salt water, for example)
 When a mixture has a
uniform composition
throughout, it’s called
homogeneous; it is also
called a solution
Water cont. (heterogeneous
mixtures)
 A heterogeneous mixture
is one where the
components remain
distinct (you can see
them individually).
 Ex – sand and water
Water cont.
 There are two parts to a
solution: the solute and
solvent
 The solvent is what does
the dissolving, and the
solute is what dissolves
Water lab