This document discusses conjugate acid-base pairs and buffer systems. It defines conjugate acid-base pairs as two substances related by the loss or gain of a proton according to Brønsted-Lowry theory. Buffers are described as mixtures that resist changes in pH when acids or bases are added. Common buffer systems include weak acids and their salts, and weak bases and their salts. The document provides examples of conjugate acid-base pairs and buffer reactions.

1. Conjugate Acid - Base Pairs
• 2 substances related by the loss or gain of a
proton according to BrØnsted-Lowry
NH3 + HOH  NH4
+ + OH-
base conjugate
acid
acid conjugate
base
HCl + HOH  H3O+ + Cl-
base conjugate
base
acid conjugate
acid

2. • Acts either as an acid or a base
• Water & NH3 . . . . .
–Sometimes accepts an H+
–Sometimes donates an H+
Amphiprotic

3. • NH4
+ + OH-  NH3 + H2O
• CO3
2- + H2O HCO3
- + OH-
• HPO4
-2 + H2O  PO4
-3 + H3O+
Identify the conjugate pairs

4. What is the conjugate
Base for…..?
HOH
NH3
HCO3
-
Acid for…..?
HOH
NH3
HCO3
-
When finding the conj base the given
substance acts like an acid and vice versa

5. Buffers
• A buffer is a mixture of chemicals that
make a solution resist a change of pH
– pH remains relatively constant when adding
an acid or base
• A buffer is either a solution of a weak acid
and one of its salts or a weak base and one
of its salts
– The salt cation is only a spectator ion and is
not involved in the reaction

6. Buffer Capacity
• There comes a point when the buffer is
“used up” “reached its capacity”
• It can no longer take H+ ions (or OH-)
out of solution and the pH begins to
change

7. • This is important when the system is fragile
– Bloodstream pH is between 7.3 - 7.5
– If < 6.9 or > 7.7 the person dies
• Buffer aids in maintaining homeostasis of
the individual
• The buffer species in the blood is
carbonic acid / hydrogen carbonate ion
H2CO3 / HCO3
-

8. • If the blood is too basic (alkaline), the
reaction decreases the amount of OH-
in the bloodstream
H2CO3 + OH-  HOH + HCO3
-
• If excess H+ is in the blood, the rxn
decreases it
H+ + HCO3
-  H2CO3

9. Practice
• Write an equation to show the addition of
an acid and a base to the following buffer
systems
NH4
+ / NH3
CH3COOH / CH3COO-
H2PO4
- / HPO4
-

10. THE END