Chapter 2-2
Properties of Water
A. The most abundant compound in living material is
water.
1. It makes up about 75% of protoplasm.
2. Water is considered an inorganic compound. That
means it does not contain carbon. Carbon compounds are
called organic compounds and are often associated with living
organisms.
3. Water is composed of hydrogen and oxygen. There is a
2: 1 ratio between hydrogen and oxygen.
4. Water functions as a universal solvent, a transportation
fluid, and allows for chemical reactions to occur.
5.
It can do all of these functions because of water’s
unique properties.
a.
Polar molecule- all molecules are neutral in charge
(the number of positive charges must equal the number of
negative charges). However, the charges in some molecules
are not evenly spread in the molecule, leaving areas that
appear to have a slight charge. These are called polar
molecules. This uneven balance of charge is caused by some
atoms having a stronger pull on the shared electrons.
+
-
+
b. Hydrogen bonding- because of the slight charges on
the opposite ends of the water molecule other polar molecules
are attracted to the positive and negative charges. These are
relatively weak attractions when compared to ionic or
covalent bonds, but they are the strongest bonds that form
between water molecules.
H bond
+
c.
Cohesion is an attraction between
molecules of the same substance. Because
of H bonding, water is extremely
cohesive.
d. Adhesion is an
attraction between
molecules of different
substances. The meniscus
in a graduated cylinder is
produced by the adhesion
of water to the glass
surface. Capillary action is
also caused by adhesion.
B.
Solutions and Suspensions
1. Mixture- a material composed of two or more
substances that are not chemically combined.
a.
Examples: salt & pepper, sugar and salt, ice tea and
sugar, atmosphere, fog, and metal alloys.
b.
2 types of mixtures:
1. solution- is a mixture in which all parts are evenly
spread throughout the solution.
2. suspension- a mixture in which the materials do not
dissolve (go into solution) but remain in very small pieces
that float.
1. solution- is a mixture in which all parts are evenly
spread throughout the solution.
a) Example: sugar dissolved in ice tea (water)
b) There are 2 parts to a solution:
1) solute- the substance that is dissolved
2) solvent- the substance in which the solute dissolves.
Cl-
Cl-
Na+
Na+
Water
Water
Cl-
Cl-
Na+
Na+
Water
Water
2. suspension- a mixture in which the materials do not
dissolve (go into solution) but remain in very small pieces
that float.
a) example; blood
C.
Acids, Bases, and pH
1. Water molecules can dissociate to form ions. It will
form as many positive ions and it does negative ions, so it is
considered neutral.
OHH+
H2O ----> H+ + HOH+
H+
OH-
H+
OH-
H+
OH-
OHOHH+
OH-
H+
2. pH scale- is a measurement system that measures the
concentration of H+ ions in a solution.
pH scale
basic
acidic
neutral
0
1
2
3
H+
4
5
>
6
7
8
H+= OH-
9
10 11 12 13 14
<
OH-
The pH scale goes from 0-14, 7 is neutral. 0 7 acidic
and 7  14 basic.
a.
Solutions that have more H+ than water are called
acids.
1. The greater the number of H+ the lower the
measurement. The lower the measurement, the stronger the
acid.
pH scale
acidic
basic
neutral
0
1
2
3
H+
4
5
>
6
7
8
H+ = OH-
9
10 11 12 13 14
<
OH-
b.
Solutions that have less H+ than water are called bases.
1. The fewer H+ the higher the measurement, the higher
the measurement, the stronger the base.
pH scale
acidic
basic
neutral
0
1
2
3
H+
4
5
>
6
7
8
H+ = OH-
9
10 11 12 13 14
<
OH-
c.
The pH scale goes from 0-14, 7 is neutral. 0 7 acidic
and 7  14 basic.
pH scale
acidic
basic
neutral
0
1
2
3
H+
4
5
>
6
7
8
H+ = OH-
9
10 11 12 13 14
<
OH-
d. Buffer- buffers are substances that absorbs H+ when
the pH goes down and release H+ when the pH goes up.
They are usually weak acids or bases that can react with
strong acids or bases to prevent sharp, sudden changes in pH.
These are common inside the body or in the blood stream and
help maintain internal homeostasis.