Acids and Bases
Acids and Bases
pH is measure of the concentration of hydrogen [H+] ions in solution. The pH
scale is based on exponents of ten. The difference between pH 5 and pH 6
is a power of 10. Indicators are weak acids that change color in response to
the hydrogen ion concentration. Litmus, a compound extracted from lichens, is a
common indicator. There are other wide range indicators that offer a
spectrum of colors to differentiate the pH of acids or bases.
Substances with a pH of less than 7 are acidic. Substances with a pH of 7
are neutral.
Substances with pH greater than 7 are alkaline (another word for base).
TRY THIS "Acids Alkalis and Neutralisation" on-line lab simulation (Note the British
spelling)
Acids
Acids release hydrogen ions in water solution.
- Acids have a pH less than 7.
- Acids react with metals to release hydrogen gas.
- Acids react with carbonate compounds releasing carbon dioxide.
- Acids taste sour, burn to the touch, and conduct electricity.
- Acids turn blue litmus paper red.
Bases
Bases release hydroxide ions in water solution. However, some bases do
not not have a hydroxide ion. Therefore, another definition of base is that a
base is a hydrogen ion acceptor in water solution.
- The pH of a base is greater than 7.
- Bases taste bitter and feel slippery to the touch, and conduct electricity.
- Bases do not react with metals or carbonate compounds.
- Bases turn red litmus paper blue.
Acid-Base Reactions
Acids and bases react with each other to form water and salts. When the
concentration of hydrogen ions equals the concentration of hydroxide ions a
neutral pH of 7 is attained.
Weak or Strong Acids and Weak or Strong Bases
Initially, the terms weak or strong acid and weak or strong base referred to the
ability of an acid or base to conduct electricity. If an acid or base is a good
conductor of electricity is called a strong acid or strong base. If an acid
or base is a poor conductor of electricity is called a weak acid or weak base.
Today, weak and strong refer to the ability of an acid or base to form ions in water
solution.
Strong acids readily ionize in water. Hydrochloric acid is a strong acid.
Organic acids tend to remain as molecules in solution rather than breaking up
into ions. They are examples of weak acids. Strong bases such as sodium
hydroxide form ions in water. Sodium bicarbonate is an example of a weak base.
The terms dilute and concentrated are used to describe the moles of acids or
bases compared to moles of water in a solution.
Acid Rain
When rain water falls through air it mixes with carbon dioxide. This forms a weak
carbonic acid. Rain water has a pH between 5.6 and 6.0. The term acid rain
refers to rain water that has a pH lower than 5.6. Acid rain forms when sulfur
dioxide and nitrogen dioxide form sulfuric acid and nitric acid in the
atmosphere. Although volcanic eruptions releases compounds capable of
producing acid rain, the main source of acid rain producing compounds is human
activity.
Human Digestion
Digestion is the breakdown of food into substances necessary to sustain life. Mechanical digestion is the grinding and churning of food particles. Mechanical digestion
takes place in the mouth and stomach. Chemical digestion uses acids, bases,
and enzymes to breakdown food particles into fundamental compounds such
as amino acids, glucose, and nucleic acids. Changes in pH allow enzymes
to work more efficiently.
