Lecture 19.5 for PREP Chemistry

1. A buffer is a solution that resists changes in
pH when moderate amounts of acids or
bases are added.

2. Buffer solutions are prepared by mixing
a weak acid with its conjugate base
or
a weak base with its conjugate acid

3. Buffer solutions are prepared by mixing
a weak acid with its conjugate base
or
a weak base with its conjugate acid
Buffers can neutralize both OH– and H+
when one of these ions is added to the
buffered solution.

4. A buffer solution can be prepared by
using the weak base ammonia, NH3, and
an ammonium salt, such as NH4Cl.

5. A buffer solution can be prepared by
using the weak base ammonia, NH3, and
an ammonium salt, such as NH4Cl.
• When acid is added, NH3 reacts with H+.
NH3 + H+  NH4+

6. A buffer solution can be prepared by
using the weak base ammonia, NH3, and
an ammonium salt, such as NH4Cl.
• When acid is added, NH3 reacts with H+.
NH3 + H+  NH4+
• If a base is added, the NH4+ ion from the
–
salt reacts with the OH .
NH4+ + OH-  NH3 + H2O

7. Another buffer system contains the weak
acid acetic acid, HC2H3O2, and the salt
sodium acetate, NaC2H3O2.

8. Another buffer system contains the weak
acid acetic acid, HC2H3O2, and the salt
sodium acetate, NaC2H3O2.
• If base is added, the weak acid reacts to
neutralize the addition.
HC2H3O2 + OH-  C2H3O2- + H2O

9. Another buffer system contains the weak
acid acetic acid, HC2H3O2, and the salt
sodium acetate, NaC2H3O2.
• If base is added, the weak acid reacts to
neutralize the addition.
HC2H3O2 + OH-  C2H3O2- + H2O
• If acid is added, the acetate ion from the
NaC2H3O2 will neutralize the added H+.
C2H3O2- + H+  HC2H3O2