Buffer Demonstration 1: Weak Acid and its Salt

Introduction to Buffers. We start with two solutions with the same pH (around 5):
A - ethanoic acid & sodium ethanoate mixture
B - hydrochloric acid
The effect of (i) 1 M sodium hydroxide, and (ii) 1 M hydrochloric acid on the pH is demonstrated. The solutions behave very differently, but can you explain why?