Biochemistry: Acids, Bases and Buffers

1. Acids- substances that release H+ when they dissolve in water/in solution. Acids add H+ .
a. Example: Hydrochloric acid HCl, HCl in water dissociates (splits) into H + and Cl -
.
2. Bases- substances that remove H+ directly or by releasing hydroxides (OH -
). Bases remove H +
.
a. The hydroxide (OH- ) released by some bases reacts with H+ in solution to produce water
(H2O). This reaction removes the H + from the solution.
b. Example A: Ammonia (NH 3)- see slide 3
i. Removes H + directly by binding to it.
c. Example B: Sodium Hydroxide (NaOH)- see slide 3
i. Removes H + by releasing OH - which reacts with the H+ producing water (it neutralizes
the H+ ).
3. pH- measure of the acidity of a solution.
a. The acidity of a solution depends on the concentration of H+ (hydrogen cation, hydrogen
ion, or a proton).
b. pH is calculated with the formula:
i. pH = -log (H + concentration)
c. pH is a 0-14 scale- see slide 4
i. The relationship between pH and H+ (acidity) is inverse:
1. The lower the pH the more acidic, the higher the pH the less acidic.
a. 1 = very acidic
b. 14 = not very acidic/very basic
2. ↑ H + (acidity) = ↓ pH
a. Acids add H+ to solution and ↓ pH
3. ↓ H + (acidity) = ↑ pH
a. Bases remove H + from solution and ↑ pH
ii. pH 7 is a neutral pH. This is an equilibrium between H+ and OH- .
d. The normal pH range for most body fluids is 7.35 to 7.45.
i. If you cannot maintain pH within the narrow range = disease:
1. Acidosis- body fluid pH chronically below 7.35
2. Alkalosis- body fluid pH chronically above 7.45
4. Buffers- a buffer is a combination of a weak acid and its conjugate base or a combination of a
weak base and it’s conjugate acid. The purpose of a buffer in a solution is to resist changes in pH
when acid or base are added to the solution. In simple terms think of a buffer as a substance in a
solution that has acid and base. Because the buffer has both acid and base it can neutralize any
added acid (with the base) or any added base (with the acid). Buffers essentially remove
whatever was added and as a result prevent any changes in pH.
5. Buffers is the Human Body
a. Buffers are important in body fluids because they protect body fluids from large
fluctuations in body fluid pH (which would be a lack of homeostasis remember?)
b. There are two buffer systems in the human body:
i. The Chemical Buffer Systems

1. The chemical buffer systems are buffers directly in body fluids. They can
respond to added acid or base very quickly. They can also be overwhelmed by
too much added acid or base.
2. There are three chemical buffer systems in body fluids:
a. The Carbonic acid/Bicarbonate Buffer System
i. Buffer system in the extracellular fluid (fluid outside cells)
b. The Phosphate Buffer System
i. The Buffer system in the intracellular fluid (fluid inside cells)
c. The Protein Buffer System
i. The buffer system in the extracellular and intracellular fluid.
ii. The Physiological Buffer Systems
1. The physiological buffer systems are entire organ systems that act as buffers.
2. There are two physiological buffer systems:
a. The Respiratory System
i. Regulates the pH of body fluids by controlling the concentration of
carbon dioxide (CO2)
ii. What does CO2 have to do with pH? CO2 reacts with water to
make acid in all body fluid and, as a result, can alter pH.
b. The Urinary System
i. Regulates the pH of body fluids by saving or eliminating H + and
bicarbonate (a base) from the body in urine.