Question

What name is given to substances that resist changes in pH?

Answer 1

If we add a small amount of acid or base into a solution, if the pH of the solution doesn't change then it is a solution made up of a conjugate base and conjugate acid added in such a way that the solution is in equilibrium.

Complete answer:
pH is a property by which we can identify whether the given compound is acid, base, or neutral. Generally acid is a substance that has hydrogen ion which is released when dissolved in water, it has a sour taste, and it turns the blue litmus paper to red and base is a substance that has hydroxyl ion which is released when dissolved in water, it has a bitter taste, and it turns the red litmus paper to blue.
On a pH meter, the acid has a low value, i.e., 0 – 6.9, and the base has a high value, i.e., 7.1 – 14.
If we add a small amount of acid or base into a solution if the pH of the solution doesn't change then it is a solution made up of a conjugate base and conjugate acid added in such a way that the solution is in equilibrium. This solution is known as buffer solution and the property of retaining the pH of the solution even after the addition of acid or base is known as buffer action.

Note:
There are many types of buffer like acid buffer, examples are the mixture of acetic acid and sodium acetate ($C{{H}_{3}}COOH\text{ and }C{{H}_{3}}COONa$), a mixture of formic acid and sodium formate ($HCOOH\text{ and }HCOONa$), etc, and base buffer, an example is the mixture of ammonium hydroxide and ammonium chloride ($\text{N}{{\text{H}}_{4}}\text{OH and N}{{\text{H}}_{4}}Cl$), etc.