How do you use phenophthalein to test for acids and bases?

Answer 1

Any titration is done to find the "equivalence point" - where the amount of titrant (strong base in your question) is equal to the amount of unknown (weak acid in your question). When the two are equal, the base has converted all the weak acid into it's conjugate base.

An indicator should change color over the pH range that includes the equivalence point. In your question, when using a weak acid, what's left at the equivalence point is a strong conjugate base. The solution will have a slightly basic pH.

Phenolphthalein has a colorless to pink transition over the range of pH 8-9.6, which is slightly basic. So it changes color across the equivalence point. So it makes a good indicator for the scenario you asked about.

Thymol blue (color change slightly lower pH, weaker base, stronger acid) or Thymolphthalein (color change slightly higher pH, stronger base, weaker acid) may also be good choices.

Answer 2

Any titration is done to find the "equivalence point" - where the amount of titrant (strong base in your question) is equal to the amount of unknown (weak acid in your question). When the two are equal, the base has converted all the weak acid into it's conjugate base.

An indicator should change color over the pH range that includes the equivalence point. In your question, when using a weak acid, what's left at the equivalence point is a strong conjugate base. The solution will have a slightly basic pH.

Phenolphthalein has a colorless to pink transition over the range of pH 8-9.6, which is slightly basic. So it changes color across the equivalence point. So it makes a good indicator for the scenario you asked about.

Thymol blue (color change slightly lower pH, weaker base, stronger acid) or Thymolphthalein (color change slightly higher pH, stronger base, weaker acid) may also be good choices.

Answer 3

Phenolphthalein can be used as an acid-base indicator to determine the acidity or alkalinity of a solution. In acidic solutions, phenolphthalein remains colorless, while in basic solutions it turns pink or purple. By adding phenolphthalein to a solution and observing the color change, you can determine whether the solution is acidic or basic.

Answer 4

It is an indicator that turns pink when a solution becomes basic. but remains clear for acids. It is useful when doing a titration and testing for the endpoint of neutralization.

Answer 5

Add 1 drop of phenolphthalein to the substance. If it remains colorless it is acidic (or less than pH 8 to be accurate). If it turns pink, the substance is a base.

Answer 6

Be pink/purple