What is the difference between pressure and force?

Buffer solution

Its pH resists change : That means that if we add a small amount of acid or base, the pH of the solution remains the same.

Such solution can be made with a solution of weak acid and its salt with a strong base:

Example: acetic acid and sodium acetate

sodium acetate dissociates completely:

CH3C00Na --> CH3C00- + Na+

If acid is added, the extra hydrogen will be picked up by the CH3C00-

If base is added, the OH- will be neutralized by the hydrogens from the acid.

So, the result is that the pH remains unchanged with the addition of small amounts of acid or base.