Final answer:
The addition of 5 drops of 0.10 M NaOH to 20 mL of a buffer solution likely caused a slight increase in pH due to the neutralization of OH- ions by the buffering components. The buffer's ability to maintain pH prevents significant pH changes.
Step-by-step explanation:
When 5 drops of 0.10 M NaOH were added to 20 mL of a buffer solution, the pH of the solution likely increased. However, due to the buffering action, this increase in pH would be very small compared to the change that would have occurred in distilled water. Buffers are designed to maintain a relatively constant pH, so they resist changes in pH when small amounts of acids or bases are added. Given that the buffer used here is similar to the one mentioned in the reference, which contained equal concentrations of acetic acid (CH3COOH) and its conjugate base acetate (CH3COO-), the added hydroxide ions (OH-) from the NaOH would be neutralized by the acetic acid present in the buffer. This reaction would form water and more acetate ions, thus having a negligible effect on the pH. Nonetheless, if excessive amounts of a strong base are added, eventually the buffer capacity could be exceeded, resulting in a more significant pH increase.