1. Define electrolytes, acids, and bases. 2. What does pH measure? 3. Define the pH of a solution.
Acids, Bases,
and the pH Scale
Acids are electrolytes
that release
hydrogen ions (H+) in water. An example of an acid is hydrochloric acid, made
up of hydrogen and chloride ions. Bases are electrolytes that release hydroxide (OH–) ions that
bond with hydrogen ions. An example of a base is sodium hydroxide (NaOH), made
up of sodium, oxy-gen, and hydrogen ions. In body fluids, the concentra-tions
of hydrogen and hydroxide ions affect chemical reactions by a considerable
amount. These reactions control certain physiological functions such as blood
pressure and breathing rates.
The bicarbonate
ion (HCO3–) is important
in the human body, and found in large amounts in the blood. Ammonia (NH3)
is a base that is also a waste product of the body’s breakdown of protein.
Ammonia has one pair of unshared
electrons that have a strong ability to attract protons. When a pro-ton is
accepted, ammonia becomes an ammonium ion (NH4+) in the following
process:
NH3+ H+→ NH4+
Hydrogen ion concentrations in
body fluids are vital, and can be measured by the value pH. It is expressed in a type of
mathematical shorthand based on concentrations calculated in moles per liter
(with a mole representing an amount of solute in a solution). The pH of a
solution is defined as the level of acidity or basicity. The pH scale ranges
from 0 to 14, with 7 being the midpoint (meaning it has equal numbers of
hydrogen and hydroxide ions). Pure water has a pH of 7, and this midpoint is
considered to be neutral (nei-ther acidic nor basic). Therefore, a solution
contains an equal number of hydrogen ions and hydroxide ions are neutral.
Measurements of less than 7 pH are con-sidered acidic, meaning there are more
hydrogen ions than hydroxide ions. Measurements of more than 7 pH are
considered basic, also known as alkaline, meaning there are more hydroxide ions
than hydrogen ions.
The pH of blood usually ranges
from 7.35 to 7.45. Abnormal fluctuations in pH can damage cells and tis-sues,
change the shapes of proteins, and alter cellular functions. Acidosis is an abnormal physiological
state caused by blood pH that is lower than 7.35. If pH falls below 7, coma may
occur. The two different types of acidosis are metabolic and respiratory.
Metabolic aci-dosis is a condition in which the kidneys are not able to remove
ketone bodies, which are metabolites of fats. In patients with type 1 diabetes,
the body may be producing too many ketone bodies. Respiratory aci-dosis occurs
in patients suffering from chronic lung diseases such as emphysema or chronic
bronchitis. Higher carbon dioxide concentrations in the blood results in blood
pH decreasing.
Alkalosis results from blood pH that is higher than7.45. If pH rises above 7.8, it generally causes uncon-trollable and sustained skeletal muscle contractions. Alkalosis also may be metabolic or respiratory. Meta-bolic alkalosis involves elevations of tissue pH, either as a result of decreased hydrogen ion concentration or a direct result of increased bicarbonate concen-trations. Respiratory alkalosis is caused by increased respiration, which elevates the blood pH. It may be caused by pneumonia, stroke, meningitis, fever, and pregnancy.
Chemicals that resist pH changes are called buf-fers. They combine with hydrogen ions when theseions are excessive and contribute hydrogen ions when these ions are reduced. FIGURE 2-6 shows the pH val-ues of acids and bases. An example of a buffer that is important in body fluids is sodium bicarbonate.
1. Define
electrolytes, acids, and bases.
2. What
does pH measure?
3. Define
the pH of a solution.
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