MYP Biology:
Water & It’s Properties
Water is Essential to Life on Earth
It is the ONLY substance on Earth that can
be found naturally-occurring in all states
of matter…
It makes up 60% of your body, 70% of your
brain, and 80% of your blood…
It covers more than 70% of the planet, but less
than 3% of it is drinkable…
What is the Structure of a Water Molecule?
•H₂O
• 2 Hydrogen + 1 Oxygen
• These atoms are linked together by
COVALENT bonds in which they share
electrons
What is the structure of a water molecule?
Hydrogen Atoms
Covalent Bond
Oxygen Atom
Water is a Polar Molecule
A Polar molecule
has positive and
negative “poles”
due to unequal
sharing of electrons
in Covalent bonds
Water is a Polar Molecule
The larger atom(s) (Oxygen)
pull more of the electrons
toward it and takes on a
negative (-) partial charge
The smaller atom(s) (Hydrogen)
have electrons pulled away
from them and take on a slight
positive (+) partial charge
Water makes Hydrogen Bonds
Hydrogen bonds are
between the oppositely
charged ends of polar
molecules (like water!)
Oxygen Atom
Hydrogen Atom
Covalent Bond
Hydrogen Bond
Many Compounds Dissolve in Water
• Substances, like water, that
other compounds dissolve in
are called SOLVENTS.
• The compounds being dissolved
in the solvent are called
SOLUTES.
• Solutes and solvents mix
together to form a SOLUTION.
A Solution: Salt & Water
SOLUTE (Salt)
SOLVENT
(Water)
Many Compounds Dissolve in Water
• Polar solvents dissolve
POLAR solutes
• Nonpolar solvents
dissolve NONPOLAR
solutes
• Polar & Nonpolar do
NOT mix…
Some Compounds form ACIDS or BASES
• Acids release Hydrogen Ions (H+) when
they dissolve in water
• Bases remove Hydrogen Ions (H+) when
they dissolve in water
Some Compounds form ACIDS or BASES
The pH Scale identifies how basic or acidic
a solution is. The scale runs from 0 to 14.
• Less than 7 = ACIDIC
• 7 = neutral
• Higher than 7 = BASIC (Alkaline)
stomach acid pH between 1 and 3
more acidic
bile pH between 8 and 9
more basic
Water has many special properties
ADHESION & COHESION
Water molecules demonstrate ADHESION
in their ability to stick to other surfaces and
COHESION in their ability to stick to each
other. This is due to the strong Hydrogen
bonds they make.
Water has many special properties
SURFACE TENSION
The adhesive and cohesive properties
of water produce SURFACE TENSION,
or the ability of water molecules to
form a thin surface ‘skin.’
Water has many special properties
HIGH SPECIFIC HEAT
Water changes temperatures very SLOWLY.
This is because it requires a large amount
of energy to disrupt water’s strong
network of Hydrogen bonds.
Water has many special properties
• In most cases, the SOLID state of matter is the
most dense:
• But water is a special case…
Water has many special properties
SOLID Water is LESS Dense than LIQUID Water
Due to the geometry of the Hydrogen bonds
between water molecules, solid water (ice), is
less DENSE than liquid water—so it floats!
Water has many special properties
“UNIVERSAL” SOLVENT
Since it is a POLAR molecule with
neutral pH value, water is an excellent
solvent and is able to dissolve most
compounds.
Water’s properties make it essential to life
• Adhesion / Cohesion
– Water flows through tubes/
vessels from roots to tree-tops
which allows plants to grow
taller and transport water
Water’s properties make it essential to life
• Surface Tension
– Organisms can move
across and live on top of
bodies of water
Water’s properties make it essential to life
• High Specific Heat
– Stable environment for marine organisms
– Acts as effective coolant (sweating)
– Helps maintain homeostasis in terms of organism
body temperature
Water’s properties make it essential to life
• Ice is less dense than
liquid water (floats)
– Prevents water habitats
from freezing solid
– Preserves liquid water in
colder temperatures
– Ice reflects sunlight and
regulates global temp.
Water’s properties make it essential to life
• “Universal” Solvent
– Dissolves and transports
nutrients, gases, and
waste through bodies of
organisms and habitats
Check for Understanding!
• Acid, Base, or Neutral?
pH = 7
pH = 3
pH = 13
Check for Understanding!
Oxygen Atom
Hydrogen Atom
Covalent Bond
Hydrogen Bond
Check for Understanding!
Check for Understanding!
Hot Water + Hot Chocolate Mix = Hot
Chocolate
Solvent =
Water
Solute =
Chocolate Mix
Solution =
Hot Chocolate
The End…