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Chemistry Lab

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Last week, I did titration of Zn with EDTA experiment. I used calmigte as the indictor. The endpoint of this titration is supposed to be blue. The color change go from wine-red to violet to Blue. I did a mistake by stopping the titration at the violet color. Is there anyway to estimate how many mL I am away from the Blue end-point. Thanks.

  • Chemistry Lab - ,

    The only thing I can suggest is to use the numbers you have, assume that is the end point, and calculate the amount of Zn in your sample. Then weigh an amount of Zn or Zn salt equal to the amount you have calculated as being in your sample, add the same materials as you did to the unknown, titrate to the same color that you titrated to the first time, then count the drops of titrant from that point in the titration to the suggested end point color. That won't get it exactly but it should be a close approximation. The problem with this estimation and that you have only your "memory" as to the color you titrated to the first time. And I can tell you that the eyes are not that good at remembering a color that is not a sharp color change. My advice to students who did this was to start over. If this is a lab report you are doing, I suspect starting over is not an option; hence you want to estimate. And you may not have the option, even, of doing the estimation procedure I've outlined above. The simple answer to your question initially is "no."

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