Unique
Attributes
of Water
Chapter 2,
Part 2

Water covers 75% of the Earth’s surface.
Water is unusual because it is the only compound
which exists commonly in all three states of
matter.

Gas (water vapor)

Solid (ice)

Liquid (fluid water)
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Water is a critical component of living
systems.

Water dominates the intracellular
environment.
◦ 75-85% of the cytoplasm of a plant or animal cell is
water.
◦ In some organisms, like jellyfish, this value exceeds
95%.

In many biological reactions, the H+
OH- of water or are pulled off organic
molecules to synthesize water.
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Individual water molecules are polar molecules because
of the electronegativity difference between hydrogen
and oxygen.
Because of this, water molecules easily form hydrogen
bonds with other water molecules or with polar or
charged compounds
One water molecule can form
hydrogen bonds with up to
four other water molecules.
Water has a number of
interesting physical
properties because of the
importance of hydrogen
bonds.
Na+--
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At any one time any water molecule forms
hydrogen bonds with several others, with bonds
forming and breaking constantly (in liquid).
Cohesion is a measure of the “stickiness” among
molecules of the same type.
◦ Water molecules have a high level of cohesion
because of these hydrogen bonds that form
among molecules.
Adhesion is the tendency of one substance to cling
to another substance.
◦ Because of hydrogen bonding, water adheres to a
wide variety of other substances, such as many
biological molecules.
◦ But not at all to others, such as oils.

Water has a high specific heat, which means it
will absorb a lot of energy before the
temperature of the water changes.
◦ It takes energy to break apart the hydrogen bonds
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
The specific heat of water is 4.184 J/g°C,
while Tungsten’s specific heat 0.134 J/g°C.
Since humans are 60%, we have a high
specific heat. This is why our temperature is
fairly constant at 98.6°.


A mixture is matter that contains two or more
substances are not in set proportions
A solution is a liquid that contains a
homogeneous mix of two or more
substances.
Matter
Pure
substances
Compounds
Mixtures
Elements
Homogenous
Mixtures
Heterogeneous
Mixture
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Chicken Noodle Soup
Milk
O2
Diamond
Carbon Dioxide
Salt
Salt Water
Bronze

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An aqueous solution is a solid, liquid, or gas
dissolved in water.
The concentration of a solution is the relative
amounts of solute and solvent.
◦ ↑ solute in solution, the more concentrated
◦ ↓ solute in solution, the less concentrated
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Water (H2O) is a good solvent for some
substances, but poor for others.
Molecules that have regions of polar covalent
bond or ionic dissolve well? Or not well?
Hydrophilic (water-loving) materials where
water molecules surround the materials with
hydrogen bonds.
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When salt (NaCl) is added to water, groups of water
molecules form _________ bonds with Na+ and Cl-.
These hydrogen bonds between
water and ions pull the ions
_____________ from the salt.
Water’s ability to dissolve
hydrophilic compounds is limited.
Eventually, there are no more
__________ water molecules to
form new hydrogen bonds and
the solution is saturated.
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Molecules that are dominated by non-polar
covalent bonds do not form hydrogen bonds and
do not dissolve in water.
Examples of these hydrophobic (water-fearing)
compounds are oils and fats.
Water molecules will push hydrophobic molecules
together to reduce water’s surface area (lowering
surface tension).
Sprinkle oil droplets on water and eventually they
will ______________ into one large drop.
Hydrophobic lipids are the major constituent of cell
membranes.

Among all the molecules in 1 liter of water
are a few in which oxygen has stolen the
shared electrons completely from one
hydrogen atom.
 H2O⇆

H+ + OH-
At any one time, 1 in every 554 million water
molecules has dissociated into a hydrogen
cation (H+) and a hydroxide anion (OH-).


A chemical equation is a way of describing
what happens in a chemical reaction.
Equation for Photosynthesis

Light + 6CO2 + 6H2O
Reactants

→
C6H12O6 + 6O2
Products
The arrow indicates the direction the
chemical equation is occurring. Most often
said as “yields”.


Dehydration Synthesis Reaction is a chemical
change where water is released and a larger,
more complex molecule is made
(synthesized).
NH2CH2CO-OH + H-NHCH2CO-OH →
 NH2CH2CO-NHCH2CO-OH +H-OH

Hydrolysis Reaction is where water is used to
break the reactants into smaller, less complex
products
◦ NH2CH2CO-NHCH2CO-OH + H-OH →
 CH2CH2CO-OH + NHCH2COO-OH
An acid is any substance that
________________ the [H+] in a solution.
 In water, an ionic compound, like HCl, will separate
into H+ and Cl- ions, increasing the concentration
of H+.
 Most acids are “proton donors”.
 A base is any substance that _________ the [H+] in a
solution.
 Some bases remove H + directly:
◦ NH3 + H+ <----> NH4+
 These bases are “proton acceptors
 Others are more indirect:
 NaOH <---> Na+ + OHOH- + H+ <---> H2O

HCl
 NaOH
 KOH
 H2SO4
CH3COOH



In biological systems, the hydrogen ion
concentration varies over a huge range of values,
by 100 million or more.
◦ For example, the concentration of hydrogen ions in the
stomach is 1,000,000 times greater than that in the _______


To encompass that range of variation (so many
zeroes), the pH scale was developed.
 pH = -log10 [H+] or [H+] = 10-pH
Because the pH values are measured on a log scale
a change of pH from 7 to 5 represents a 100x
increase in [H+].
◦ The change is 2 pH units: 102 = 100.
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A solution with a pH between 0
and 7 is acidic
A solution with a pH between
7 and 14 is basic.
The intracellular pH is 7.3-7.4
If we add acid to the solution, [H+]
will increase (the exponent will be
less negative) and pH values will
be smaller (moving toward 1).
If we add base to a solution, the
[H+] will decrease (the exponent
will be more negative) and pH
values will be larger
(moving up to 14).

Salts are ionic compounds that do not release
either H+ or OH- when dissolved in water.
Usually a product (along with water) of a
reaction between an acid and a base. In
chemistry, a salt is any metal combining with
a non-metal.
◦ HCl + NaOH → Na+ + Cl- + H+ + OH- → NaCl + H20
◦ Examples of Salts:
 Potassium Chloride (KCl)
 Calcium Chloride (CaCl2)
 Copper Sulfate (CuSO4)
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
Many normal cellular processes have the
potential to release large quantities of H+ or
OH- ions.
Buffers are an aqueous solution that contain
weak acids or weak bases that tend to
maintain constant pH. This is because they
can either accept or release hydrogen ions.
H2CO3
response to increasing
[H+]
Carbonic Acid
HCO3- + H+
Bicarbonate Ion
response to
decreasing [H+]