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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: hiuky on November 28, 2004, 05:40:49 PM

Title: acid/base indicators
Post by: hiuky on November 28, 2004, 05:40:49 PM
Jsut wondering,

Why can methyl red be used as an indicator for acid-base titrations?

Title: Re:acid/base indicators
Post by: budullewraagh on November 28, 2004, 05:54:32 PM
it changes colors depending on the pH of a solution
Title: Re:acid/base indicators
Post by: sisco on December 03, 2004, 10:02:11 AM
It changes colour due to its interaction with the Oh- ions in an acid/base solution
The more alkaline the solution the more oh- ions and so the more interaction with the methylene red.
However when the methylene red changes colour does its absorption lines change?
Title: Re:acid/base indicators
Post by: Krishnan on January 29, 2005, 02:11:27 AM
Methylred is used as acid base indicator because of its sharp color change at end point especially when a weak base is used in the titration.
Title: Re:acid/base indicators
Post by: pizza1512 on February 03, 2005, 08:58:41 AM
You could use litmus paper....

Title: Re:acid/base indicators
Post by: Kong on February 04, 2005, 05:45:24 PM
When ever you are doing an acid base titration you are looking for the equivalence point.  This is the point where the number of moles of acid and base are equal.  This will help you relate an unknown quantity to a known quantity.  The equivalence point could realisically be anywhere on the pH scale.  So different indicators to different colors depending on the pH.  So depending on where your equivalence point is will determine what indicator you will want to use.  Phenolphthalien is a very popular indicator because it actually changes very close to neutral.  
   It is my estimation that indicators have been very much phased out by pH meters and will probably take one more generation to be completly eleminated.  I learned very little about them in college and a very minor occurance on the advanced placement chemistry exam.