Q:

What does phenolphthalein changing pink indicate?

A:

Phenolphthalein is an indicator that turns from clear to pink in a basic solution, according to Reference.com. In a strongly acidic solution, the indicator is orange, but in the pH range of 0 to 8.2 it is clear. The indicator is pink in solutions with a pH of 8.2 to 12, but turns colorless again in strong bases above this pH range.

Reference.com indicates that phenolphthalein is a weak acid itself that in molecular form is colorless. The addition of a base to a solution of phenolphthalein removes hydrogen ions from the solution, creating more phenolphthalein ions, which causes the color to change.

Chemists use titrations to determine the concentration of an unknown acid or base. They add the opposite reagent of known concentration and carefully measure the amount needed to cause the color change. About.com says, "For a properly performed titration, the volume difference between the end point and the equivalence point is small." At the equivalence point, V1N1 = V2N2, where V is volume and N is the concentration of the acid or base.

Reference.com says that universal indicators are a mix of phenolphthalein, and the indicators methyl red, bromothymol blue, and thymol blue. By mixing several indicators, chemists create a single solution that is useful in determining pH over a wide range.


Is this answer helpful?

Similar Questions

  • Q:

    How do you perform acid-base titration in a lab?

    A:

    Perform an acid-base titration in the lab by setting up a burette, dissolving the material for analysis in water in a flask, adding an indicator, recording an initial reading of the burette, adding titrant until the color changes and taking the final reading. The experiment usually takes less than an hour.

    Full Answer >
    Filed Under:
  • Q:

    What is the purpose of titration?

    A:

    According to Reference.com, the purpose of titration is to find the concentration of an unknown acid or base in a solution. It works by gradually combining a base of known concentration with an unknown acid solution, or vice versa, until the solution is neutralized.

    Full Answer >
    Filed Under:
  • Q:

    How accurate is a Vernier caliper?

    A:

    According to Reference.com, industrial-level vernier calipers usually provide a precision to one thousandth of an inch. In metric units, the precision is to a hundredth of a millimeter, or 10 micrometers.

    Full Answer >
    Filed Under:
  • Q:

    What do shifting problems indicate in a car with an automatic transmission?

    A:

    Shifting problems in a car with an automatic transmission are an indicator of an issue with the transmission's internal or external components or of an electrical issue. Trouble shifting may indicate external controls that need adjustment or replacement, or it may signal that electrical components are not functioning correctly, according to AAMCO. It's also possible that shifting problems are caused by low or burnt transmission fluid, according to Mister Transmission.

    Full Answer >
    Filed Under:

Explore