What is a buffer solution?

A buffer solution is defined as a solution that resists changes in pH upon the addition of an acid or a base. This capability is crucial in maintaining a stable pH level in various chemical and biological systems, such as in the human body or in laboratory settings. Buffers typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. When an acid (H⁺ ions) is added to the solution, the conjugate base component of the buffer can react with these excess hydrogen ions, minimizing the change in pH. Conversely, when a base is introduced, the weak acid component can donate H⁺ ions to counteract the increase in pH.

The other choices describe concepts that do not accurately represent the function of a buffer solution. For example, a solution that changes color with pH pertains to indicators which signal pH changes but do not stabilize pH themselves, while a solution containing only acids would not have buffering capacity as it lacks the necessary conjugate base to mitigate changes in pH. Lastly, a solution that can cause a rapid increase in pH would not resist pH changes, which is the defining characteristic of a buffer solution.