An Introduction to Acids and Bases
Pure water is a poor conductor of electricity because it has no charged particles that are free to
move about because the hydrogen and oxygen are covalently bonded together. Actually, in water there
are a few charged particles because about 2 molecules in a billion (1,000,000,000) do break into H+ and
OH- ions, but because there are so few ions in pure water it is still a very poor conductor.
Acids and bases had been known for thousands of years but only by their outward
characteristics.
Acids
Taste Sour
Electrolyte
React with metals
React with carbonates
Change colors in indicators
Neutralize bases to form a salt and water
Above properties known as Acidic
Bases
Taste Bitter
Electrolyte
React with fats and oils
Slippery
Change colors in indicators
Neutralize acids to form a salt and water
Above properties known as Alkaline
Acids are common in many foods because most people tend to like the sour taste and acids often used
to clean metals. Because people are less attracted to the bitter taste, bases are less often found in foods
but are commonly used in cleaning products because of their reactions with fats and oils.
The following lists show some common acids and bases.
Acids
Hydrochloric
Sulfuric
Nitric
Carbonic
Acetic
Citric
Phosphoric
( HCl )
( H2SO4 )
( HNO3 )
( H2CO3 )
( HC2H3O2 )
( H3C6H5O7 )
( H3PO4 )
Bases
Sodium Hydroxide or lye
Potassium Hydroxide
Barium Hydroxide
Calcium Hydroxide
Ammonium Hydroxide
Sodium bicarbonate or
Sodium hydrogen carbonate
( NaOH )
( KOH )
( Ba(OH)2 )
( Ca(OH)2 )
( NH4OH )
( NaHCO3 )
The first modern theory of acids and bases was proposed about 125 tears ago by a Swedish
chemist named Svante Arrhenius. He saw that when you put molecules into water, sometimes they
break down and release an H+ ion. At other times, you find the release of an OH- (hydroxide) ion.
When a hydrogen ion is released, the solution becomes acidic. When a hydroxide ion is released, the
solution becomes basic. Those two special ions determine whether you are looking at an acid or a base.
For example, vinegar is also called acetic acid. (Okay, that gives away the answer.) If you look at it
when it's in water, you will see the molecule HC2H3O2 splits into H+ and C2H3O2 - ions. That hydrogen
ion is the reason it is called an acid. Chemists use the word "ionize" to describe the breakup of a
covalent compound into ions. Chemists use the word "dissociate" to describe the breakup of an ionic
compound into ions.
Since Arrhenius first proposed his theory of acids and bases there have been two other
explanations of acids and bases proposed. Both theories were proposed at about the same time about
35 years after Arrhenius. Both the Brønsted-Lowry and the Lewis theories broadened the concept of
acids and bases to chemical reactions other than in water solutions. As long as we confine ourselves to
water solutions all three theories agree. In this class we will not concern ourselves with these
additional theories because of time.
Using the Arrhenius theory we can understand why acids and bases conduct electricity when put
into water. When either an acid or base is dissolved in water it produces charged ions. It is these
charged ions which are free to move about in the water solution that allows the conduction of
electricity.
Using the Arrhenius theory we can also understand why acids and bases neutralize one another.
Let us consider what happens when we mix a solution of hydrochloric acid ( HCl ) with a solution of
sodium hydroxide or lye ( NaOH ). Arrhenius envisioned the positive sodium ion from the base
combining with the negative chlorine ion from the acid to form sodium chloride and the positive
hydrogen ion from the acid combining with the negative hydroxide ion to form H2O or water. We can
illustrate this with a simple chemical equation:
HCl
acid
+
NaOH
base

NaCl
salt
+
H2O
water
According to the simple Arrhenius theory an acid mixed with a base always yields a salt of some kind
and water, therefore we say they neutralize each other because a salt is simply an ionic compound and
water is neither and acid nor base.
Try and write an equation for the reactions between the following acids and bases:
Sulfuric acid with potassium hydroxide
Nitric acid
with ammonium hydroxide
Acetic acid
with calcium hydroxide