Solutions and pH
Introduction: Sketch the pH
scale
Solutions & Suspensions
• Water is usually part of a
mixture.
• There are two types of mixtures:
–Solutions
–Suspensions
Properties of Water
Universal Solvent
Water is the solvent of Life!
Solute – substance dissolved in a solvent to
form a solution
Solvent – fluid that dissolves solutes
Example: Ice Tea – water is the solvent
and tea and sugar the solutes
Solution
• Ionic compounds disperse as ions in
water
• Evenly distributed
• SOLUTE
– Substance that is being dissolved
• SOLVENT
– Substance into which the solute
dissolves
Solution
Suspensions
• Substances that
don’t dissolve but
separate into tiny
pieces.
• Water keeps the
pieces suspended
so they don’t
settle out.
Acids, Bases and pH
One water molecule in 550 million
naturally dissociates into a Hydrogen
Ion (H+) and a Hydroxide Ion (OH-)
H2O 
Hydrogen Ion
Acid
H+
+ OH
-
Hydroxide Ion
Base
The pH Scale
• Indicates the concentration of H+
ions
• Ranges from 0 – 14
• pH of 7 is neutral
+
• pH 0 up to 7 is acid … H
• pH above 7 – 14 is basic… OH• Each pH unit represents a factor of
10X change in concentration
• pH 3 is 10 x 10 x 10 (1000)
stronger than a pH of 6
Acids and Bases
Strength compared using pH scale
Ranges from 0 – 14
Logarithmic Scale (gets 10x bigger/smaller)
Acid – donates H+ when added to aqueous solutions
Ranges from pH 0-6.9
Base – breaks up into hydroxide (OH-) ions and
another compound when placed in an aqueous
solution
Ranges from pH 7.1 – 14
Distilled water is pH 7.0 or neutral. Why?
H2O
H+
+
OH-
Acids:
Bases:
Taste sour.
Taste bitter.
Give sharp stinging pain in a cut or
wound.
Feels slippery
Turn blue litmus paper red.
Turn red litmus paper blue.
Turn phenolphthalein colorless.
Turn phenolphthalein pink.
React with metals to produce
hydrogen gas.
React with carbonates or
bicarbonates to produce carbon
dioxide gas.
Acids
• Strong
Acids
have a pH
of 1-3
• Produce
lots of
H+ ions
Bases
• Strong
Bases have
a pH of 11
to 14
• Contain
lots of OHions and
fewer H+
ions
Buffers
• Weak acids or bases that react with
strong acids or bases to prevent
sharp, sudden changes in pH
(neutralization).
• Produced naturally by the body to
maintain homeostasis
Weak Acid
Weak Base
Acids and Bases
Buffers – compounds used to maintain a
contant pH within a system
H2CO3
Carbonic acid
H+
+
HCO3-
bicarbonate ion
Acids and Bases
Making Biological Molecules
and H2O
Condensation Reaction
H2O
Hydrolysis Reaction
Practice
When most people think of chemistry the first terms that
come to mind are acids and bases. Many of the
chemicals that people run across have some
connection to acids and bases. For instance many
people take medicine every day to cure heart burn.
These medicines are (acids/bases). One of these comes
in a blue bottle and is known as “Dr. MOM”. The
common name for this is Milk Of Magnesia Another
product claims that it is better for us to use because it
contains calcium. So in addition to helping relieve the
heartburn, it also provides us with needed calcium.
This product is called Tums and its chemical name is
__________________.
Practice
Another product that is used all the time is
Draino. Draino is a(n) (acid/base) and it has
the common name of “lye” the chemical name
is _____________________, and the chemical
formula is ___________________. This
chemical is more dangerous than the ones
used for heartburn and can cause blindness or
burns. (Acids/Bases) are also commonly used
to produce soaps and have a (bitter/sour)
taste.
Practice
Seltzer water and all sodas contain a very mild
(acid/base) known as _____________________.
This is formed by dissolving carbon dioxide in
water. The chemical formula for this substance is
___________________. Vinegar is a(n)
(acid/base) finds its way into our diet in ketchup
and most salad dressings. The chemical name for
vinegar is , the chemical formula for this
substance is ___________________.
Homework
• Keep track of what you eat today
and determine which are acids
and bases
• Bring things in from home that
you would like to test for pH
Application
• Why is it important to know about pH in
Biology?
• What happens to pH of solutions in your
body when you don’t drink enough?
• What happens to pH of solutions in your
body when you eat to many sour foods?