Question

Consider the following reactions:

1. HA + OH- = A- + H20

2. HA + H30+ = H2A+ + H20

3. HA + H20 = H30+ + A

4. HA + OH- = H3O+ + A

5. A- + H30+ = HA + OH-

6. A- + H20 = HA + OH-

7. A- + OH- HA + O2-

Which one of these reactions (enter only the reaction number, 1 to 7) is mainly responsbile for the fact that base aded to the buffer solutio causes only a very small change in pH?

Which one of the above reactions (enter only the reaction number, 1 to 7) is mainly responsbile for the fact that buffer solutions can also react witha small amount of strong acid, H30+, without a large change in pH?

Answer 1

Buffers are solutions that resist change to pH upon addition of small amounts of either an acid or a base.

Consider the following reactions:

4. HA + OH^- ----> H₃O⁺ + A^-

In the above reaction conjugate acid neutralizes added strong base thus, responsbile for the fact that base added to the buffer solution causes only a very small change in pH.

Consider the following reactions:

5. A^- + H₃O⁺ ----> HA + OH^-

The pH does not change very much because (A^-] I (HA] does not change very much.

As the amount of strong acid added is small as compared to the amount of conjugate base in the buffer . Therefore,the above reaction(5) is mainly responsbile for the fact that buffer solutions can also react with a small amount of strong acid, H₃O⁺, without a large change in pH.