Final answer:
Phenolphthalein indicator does not significantly affect the pH of a solution; it is used to estimate the solution's pH by changing color around a specified pH level.
Step-by-step explanation:
The phenolphthalein indicator is used to estimate the pH of a solution and it changes color in response to the pH level of the solution it is added to. While adding phenolphthalein itself in the small amounts typically used for pH testing should not significantly affect the pH of the solution, the indicator does undergo a change in its ionized state depending on the pH. Phenolphthalein transitions from colorless to pink in a basic solution, typically at a pH value around 8.3, and it remains colorless in acidic solutions with higher hydronium ion concentrations.
For precise measurements, remember that phenolphthalein changes color over a range of about two pH units, not at a specific pH value. This means the indicator will begin showing a pink color when the pH of the solution is just below 8.3 and will be at its strongest color around pH 10. As a weak organic acid, the presence of phenolphthalein will not substantially change the overall pH of the substance being tested because it is such a small amount compared to the volume of the solution it's being used to test.