Titration Question

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How would adding too much indicator to a base being titrated by an acid affect the result?
Can I list it as a possible error?
If not, can someone please suggest another one? please also say how it would affect the outcome of the experiment and how i would be able to minimise it.

Thanks :)
 

Answers and Replies

  • #2
symbolipoint
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The indicator itself is either a weak acid or a weak base. Adding too much indicator will force your titration to significantly include the indicator an an interfering analyte component competing with your titrant against the acid or base which you are expecting to measure.

If you can comfortably do the titration monitoring with a pH meter, then you could titrate without a colored indicator.
 
  • #3
Borek
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  • #4
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we used methly orange
 
  • #5
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it can also alter the volume...
 
  • #6
symbolipoint
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it can also alter the volume...
Just what level of material quantity is meant by "too much indicator"? A 100 ml. quantity of titration solution would usually be given no more than about 3 or 4 drops of indicator solution, hardly meaningful to the volume of the contents in the titration vessel. Greater concern for concentration would be from adding maybe 5 or more milliliters of indicator solution, but then of great concern is still how much actual indicator was present in the titration vessel to compete with the actually sought material.

Based on volume alone, I would not expect even 7 to 10 ml. of indicator to mean much; it is the amount of indicator compound that would be more of an interference.
 
  • #7
Borek
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it is the amount of indicator compound that would be more of an interference.
That's exactly the problem. Changes in volume are rarely important - many titration procedures call for dilution of the sample up to 100 or 200 mL, but it is rarely exact number, so even adding 10 mL more or less doesn't matter.
 
  • #8
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so whats the general consensus?
is it a possible error?
what im mainly concerned is whether or not it would affect a base
being titrated, since the indicator itself is a weak acid.
i know it would affect an acid (it shifts pH)
 
  • #9
Borek
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Have you read the link provided?
 
  • #10
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yeah..doesnt really specify though :/
just says that it will modify the results

sorry i just want to be sure that it is a possible error :S
 
  • #11
symbolipoint
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Methyl Orange will be in its salt form in alkaline and neutral water solution. The salt form would be yellow, but at about pH 4 and below it will be orange. Some information may be found here: http://en.wikipedia.org/wiki/Methyl_orange

If you had a solution of Methyl Orange but of uncertain concentration, yet high enough to perform a titration, let's say, of the salt form, then the solution would be yellow, probably strong yellow. You would titrate this with an acid to a color change from yellow to orange. You could determine the amount or concentration of the salt-form Methyl Orange in your sample or your solution.

Now, what if your alkaline Methyl Orange solution had a small amount of some other alkaline material present and you titrate with your acid titrant? Your color change pH transition may now depend on two materials: the large amount of Methyl Orange salt, and your other alkaline material. One or both of these materials may have steep pH changes either near or at pH 4.
 
  • #12
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so...in simple terms..?
would it be a source of error?
 
  • #13
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so in this case, would be right in saying that adding too much indictor would be a source of error since it is a weak acid and would react with the base being titrated, thus affecting the end point determined.

Or should i say something about the pH?
 
  • #14
Borek
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so in this case, would be right in saying that adding too much indictor would be a source of error since it is a weak acid and would react with the base being titrated, thus affecting the end point determined.
You should try to evaluate how large error it can produce, but you are right when it comes to general idea.

Or should i say something about the pH?
Something what?
 
  • #15
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as in the fact that it can shift the pH and subsequently the end point?
or does not that apply to this case since it is being added to a base not an acid?
 
  • #16
Borek
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as in the fact that it can shift the pH and subsequently the end point?
or does not that apply to this case since it is being added to a base not an acid?
Earlier you stated you have read the page I linked to, now you are asking things which clearly show you didn't.
 

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