Conjugate A B Pairs

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