2-1 PHYSICAL PROPERTIES OF WATER
Water

All _______________ things depend on water for their existence.

In most cells, water accounts for between _____% and _____% of the cell’s mass.
o Exceptions include _______________ and _______________ that actually
_______________ water. They can lie dormant for a long time, but
_______________ will revive them.

Proteins, polysaccharides, nucleic acids and membranes assume their characteristic
_______________ because of water.

Because water is an essential solvent and a substrate for many cellular reactions, much of
the _______________ machinery of cells operates in an aqueous environment.
Water is Polar

Draw a 3D Lewis structure for water. Identify its molecular geometry and bond angle.

Redraw it, and apply individual dipoles to the bonds. Does it have a net dipole?

The presence of a net dipole means that the molecule is _______________.
Hydrogen Bonding in Water

Polar molecules exhibit _______________ forces, specifically _______________ _______________ forces.
o If hydrogen is involved, it is called a _______________ bond.

What conclusion can be drawn about the following enthalpy of formation values?
Hf° Hydrogen Bond: –20 kJ/mol
Hf° O–H covalent bond: –460 kJ/mol

Hydrogen bonds are extremely important in biochemistry. For example, the attractions of
complementary bases in a strand of DNA are H-bonds, which help hold DNA in its
__________ __________ structure. Other intermolecular forces like __________
_______________ forces also play a role in the structures of biomolecules.

The _______________ __________ of water is 4.184 J/g°C, which is high compared to
many other liquids. A rather _______________ amount of heat is required to change the
temperature of water.
o Since 60-90% of a cell’s mass is water, this property allows temperature
fluctuations to be _______________, a critical biological feature since reaction
_______________ is sensitive to temperature changes.

The heat of _______________ of water is 539.4 cal/g, which is another property that is
much _______________ for water compared to other liquids. This means that water
must absorb this much energy from its _______________ to evaporate.
o This allows _______________ to be an effective method of _______________
body temperature since the water must remove heat energy from the body to
evaporate.
Water is an Excellent Solvent

Solute and solvent interactions are governed by the simple rule “__________
_______________ __________.”

Since water is polar, it will dissolve molecular substances that are __________ and
__________ substances that have low _______________ energy.
o These substances are called _______________ and are said to be
_______________.

Organic compounds that have polar functional groups will dissolve in water, and include
_______________, _______________ __________, __________, _______________ and
_______________ groups.
o The more __________ groups on a molecule, the more soluble it will be.
o The longer the _______________ chain on a molecule, the less soluble it will be.

The behavior of solutes in cytoplasm is different than how they behave in water.
o The _______________ of cytoplasm is higher than water because of the presence
of sugars that contain many polar hydroxyl groups.
o Charged molecules bind to each other momentarily inside cells, restricting their
_______________.
o Collisions with other molecules inhibit _______________ due to molecular
_______________.

Picture two aqueous solutions of different concentrations separated by a solventpermeable membrane. The dots represent the solute.
o The solvent will pass from the lower-concentrated solution to the higherconcentrated solution in a process called _______________.
o In order to prevent solvent flow, the _______________ of the system must be
increased. This is called _______________ pressure.
o In cells, the cell _______________ separates the highly-concentrated cytoplasm
from the surrounding aqueous environment, and prevents water from entering the
cell due to osmosis.

To prevent cell bursting due to osmotic pressure, cells may
_______________ many individual molecules into a larger
_______________. For example, 50 000 glucose molecules can be stored
as one _______________ molecule in animal cells. If enough water
entered the cell to dissolve the 50 000 glucose molecules the cell would
burst.
Nonpolar Substances

Nonpolar substances are _______________ in water. They are said to be
_______________, and the interaction between nonpolar substances and water is called
the _______________ __________.
o This is critical for the _______________ of proteins and self – _______________
of biological membranes.

Detergents (or surfactants) have a _______________ end and a _______________ end:
O
Ex:
Sodium dodecyl sulfate
+
Na
O
-
S
O
O
o These molecules are said to be _______________.
o Form micelles (shown below) – nonpolar ends trap grease and oils while the polar
end remains hydrated, allowing them to be washed away.

Some dissolved ions such as thiocyanate (SCN–) and perchlorate (ClO4–) called
_______________ enhance the solubility of nonpolar compounds in water by disordering
the water molecules.