Discovering Acids and Bases and
pH Values of Some Common
Substances
I. Discovering Acids and Bases
Science Standard: 5a, 5c
Martinez
09/11
Many solutions have certain properties
that make us call them acids or bases.
Acids
An acid is something that releases
hydrogen ions, H+, when dissolved in
water. For example: HCl in water breaks
down to H+ and Cl-
Acids are found in many foods, such as orange
juice, tomatoes, and vinegar.
An easy way to tell if a food is an acid it to taste
it; never try to taste household chemicals of any
kind to determine if they are acids.
Acids taste sour and make your mouth
pucker.
They give a sharp, stinging pain in a cut
or wound.
Acids will turn litmus paper red.
Some acids will react with metals to form
hydrogen gas.
Bases
A base is something that releases
hydroxyl ions, OH-, when dissolved in
water.
For example: NaOH in water breaks down
to Na+ and OH-
Bases are chemical opposites of acids.
They are found in many common products
around the home including soap,
ammonia, and antacids.
They tend to taste bitter (sharp).
Bases feel soapy or slippery when
touched.
Bases will turn litmus paper blue.
Salts
A salt is formed when an acid and a base
are mixed.
For example, a water solution of
hydrochloric acid (HCl) combined with a
water solution of sodium hydroxide base
(NaOH) combine to form common salt
(NaCl) and water:
HCl + NaOH --> NaCl + H2O
Litmus Paper
What is litmus paper?
Litmus paper is a modern method to
determine whether a substance is an acid
or a base.
Litmus paper has the property of changing
its color to red with acidic substances and
to blue with basic ones.
Red litmus paper looks pink and blue
litmus paper looks purple
II. pH Values of Some
Common Substances
Science Standard: 5a, 5c
Martinez
09/11
A liquid may be an acid, base, or neutral.
The degree of acidity or basicity of a
solution can be measured by using the pH
scale.
The pH scale ranges from 0 to 14.
A pH of 7 means it is a neutral solution.
Pure water has a pH of 7.
pH stands for the power of H, or the
amount of H+ ions acids or bases take or
contribute in solution.
Acids are ionic compounds (a compound
with a positive or negative charge) that
break apart in water to form a hydrogen
ion (H+).
The strength of an acid is based on the
concentration of H+ ions in the solution.
The more H+ the stronger the acid.
A pH of less than 7 means the solution is
acidic.
STRONG
WEAK
Bases are ionic compounds that break
apart to form a negatively charged
hydroxide ion (OH-) in water.
The strength of a base is determined by
the concentration of Hydroxide ions (OH-).
The greater the concentration of OHions the stronger the base.
A pH of more than 7 means the solution is
basic.
WEAK
STRONG
The less pH, the more acidic the
solution is.
VERY ACIDIC
The more pH, the more basic the
solution is.
VERY BASIC
When acids and bases are added to each
other they react to neutralize each other if
an equal number of hydrogen and
hydroxide ions are present.
When this reaction occurs, salt and water
are formed.
Each division of the pH scale either
increases or decreases the pH of a
substance 10 times. The pH of 4 is 1000
times more acidic than a pH of 7.
*Calculation 7-4 = 3.
*So multiply 10 three times: 10 x 10 x
10 = 1000 hydrogen ion concentration.