Final answer:
Acid-base indicators are unique a) because they exhibit color changes in response to the pH of the solution they are in. Examples like phenolphthalein provide visual cues during titration processes.
Step-by-step explanation:
Acid-base indicators are unique chemicals a) because they change color based on the pH level of the solution they are in.
A quintessential example is phenolphthalein, which is colorless in acidic solutions and turns pink in basic solutions.
These indicators are typically weak organic acids or bases that can exist in at least two forms, one of which will be dominant depending on the pH of the environment.
When an indicator is added to a solution, the color change occurs due to the shift in equilibrium between the protonated (acidic) and deprotonated (basic) forms of the indicator.
For instance, the universal indicator and pH paper contain a mixture of indicators that exhibit a range of colors across the pH spectrum, providing a convenient method to estimate the pH of a sample.
Practically, during an acid-base titration, indicators provide a visible sign of the equivalence point, when equivalent amounts of acid and base have been mixed.
Specific changes in color of indicators like litmus or phenolphthalein are key characteristics used to qualitatively assess the acidity or basicity of a solution.