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Titrations

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So, I've been working on my essay, and I've chosen to do an experiment of pH level of wine as it ferments. Well, there's one problem there: I have no idea how to properly do a titration measurment of pH. I'm doing the equallibrium and acid-base chemistry sections by myself (I'm in year 1, we don't do it until year two), and I'm slightly overwhelmed by everything that I have to learn. Could someone please explain titrations to me in lameman's terms, so I can get a good idea (considering I have to know how to do them by Saturday, I'm kinda stressing. :0 Thank goodness for PD days)

Any help is muchly appricated! :blum:

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Titrations are when you have a known molarity and volume of an acid or base in a burette, and the opposite in a beaker. You use an indicator in the beaker such as phenyltheline (don't remember how to spell it) and you drip the, strong acid or base until it changes colour in the beaker. At this point it is ~ at a pH of 8. This works because on the graph it has a straight line that is ~vertical around the pH of 7 range, this means that the amount of titre (known acid or base) used is the same for a pH of 8 as it is for 7. So you get the data, and when you find out the volume of titre you can find out the molarity of the unknown substance. I hope you work it out. You are making ethanol with the Wine which isn't an acid or base, but I'm sure you have worked that out. Don't use a weak acid with a weak base the curve will buffer all the time and give you no information!

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Usually titration is used to measure the concentration of the solution in question. If your intention is just to measure pH, why not simply use a pH meter (assuming your school lab has one)? So far as I know, pH is not a factor in titration. As long as one solution is acidic and one solution is basic, no matter what the pH difference is, titration will work. However,you won't be able to calculate the pH for that solution, only the amount of acidic or basic molecules that are present in the solution hence being able to determine its concentration.

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[quote name='silverks' post='17375' date='May 28 2008, 06:14 AM']Usually titration is used to measure the concentration of the solution in question. If your intention is just to measure pH, why not simply use a pH meter (assuming your school lab has one)? So far as I know, pH is not a factor in titration. As long as one solution is acidic and one solution is basic, no matter what the pH difference is, titration will work. However,you won't be able to calculate the pH for that solution, only the amount of acidic or basic molecules that are present in the solution hence being able to determine its concentration.[/quote]

True- but this statement only applies to acid/base titrations and not redox titrations. If you want to measure the pH at various fermnetation stages, the easiest way would be to use an ISE-pH meter. Note that you have to be careful in your statements here, because technically a pH meter measures the activity of hydrogen and not directly the concentration of hydrogen. In most cases, these can be taken to be equal, but technically they are not. So let me answer your question/concern with a question of my own - what do you intend to do with the pH data that you collect? If you just need a pH measurement for acidity purposes, this methodology will be fine. If you are specifically interested in proton concentration, however, you will need to covert the reported activity to yield the concentration. Harris has a good section on this. PM me for more help on this if you would like.

Booji

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i'm conducting redox itration using oat as the source of iron. when potassium permanganate is added drop by drop into the solution in the conical flask, the purple colour turn colourless until all the potassium permanganate used up. that's mean there is no pink colour form. what is mean by that? why that happen?please help...

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