Chemistry Reference
In-Depth Information
So, a very corrosive base, such as NaOH, can react with a very strong
base, such as HCl, and the products of the reaction will be salt and water!
The following equation represents an example of a neutralization reaction:
HCl + NaOH
NaCl + H
2
O
hydrochloric acid + sodium hydroxide
sodium chloride + water
Of course, if you use a different acid or a different base you won't pro-
duce table salt, but you will end up with a different type of salt, as well as
water. In order to better understand neutralization reactions, as well as
the other properties and characteristics of acids and bases, we should ex-
amine acids and bases on the atomic level.
Keep in mind that even pure substances, such as water, are made up of
particles that are in constant motion. These particles collide with each other
as well, but a chemical reaction doesn't usually take place. However, for a
certain number of particles, a reaction does take place! If two water mol-
ecules strike each other with the proper orientation and kinetic energy, a
hydrogen ion can move from one molecule to another, as shown here:
H
2
O + H
2
O
H
3
O
+
+ OH
-
water + water
hydronium + hydroxide
In this way, two neutral water molecules can react and produce a
positively charged hydronium (H
3
O
+
) ion and a negatively charged hy-
droxide (OH
-
) ion. This type of reaction, called the self-ionization of water,
is actually a relatively rare occurrence, but it does happen. You may have
measured this occurrence in the laboratory, if you ever measured the pH of
pure water. Pure water at 25
o
C has a pH of 7, which means that the con-
centration of hydronium ions, [H
3
O
+
] is 1.0 × 10
-7
moles/liter (remember
molarity?), or 1.0 × 10
-7
M. This pure water, with a pH of 7, is said to be
neutral, because it has the same number of hydronium ions and hydroxide
ions, which makes sense, because of the chemical equation shown preced-
ing this paragraph.
So, pure water at 25
o
C has a H
3
O
+
concentration of 1.0 × 10
-7
M and
an OH
-
concentration of 1.0 × 10
-7
M. The two types of ions balance each
other out. Any aqueous solution in which the concentrations of these two
ions are equal is said to be neutral.
An acid solution has a greater concentration of hydronium ions than
hydroxide ions. How does this happen? Let's suppose you added some con-
centrated HCl into your pure water sample. The HCl is a strong electro-
lyte, which means that it tends to ionize completely in aqueous solutions,
according to the reaction shown here:
