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Posted by on Wednesday, April 29, 2009 at 8:23pm.

What is a disadvantage of using pH indicators?

  • chemistry - , Wednesday, April 29, 2009 at 9:06pm

    A solution of Acetic acid has a light red color in the presense of the indicator orange IV. When sodium acetate is added to the solution, the color changes to yellow. Explain the reaction which causes the color change.

    I have no idea. Does it have to do with the sodium added? I don't understand. Help please!

  • chemistry - , Wednesday, April 29, 2009 at 9:07pm

    I don't know
    ??

  • chemistry - , Wednesday, April 29, 2009 at 11:26pm

    Disadvantage of using pH indicators for what? For titrations it is that not all indicators change at the equivalence point pH. If for determining the pH of a solution, it is because most pH indicators have a pH range of about 2 pH units which isn't very close if you want to know the pH closer than 2 pH units.

  • chemistry - , Wednesday, April 29, 2009 at 11:30pm

    Joyce, you should have posted your question separately. There is a good chance it will get overlooked by piggy backing on another question.
    The answer is that acetic acid/sodium acetate mixtures form a buffered solution. The addition of the acetate changes the pH enough that the indicator changes.
    You can calculate the change in pH if you have enough information to plug into the Henderson-Hasselbalch equation which is pH = pKa + log(base/acid).

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