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ph indicators

Postby Harpeck » Tue Jan 19, 2016 1:45 pm

When testing which ph indicator works best between red cabbage, red onion, and blueberries, how can you tell which works best? How can you be sure which one is giving you the most accurate results?

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Re: ph indicators

Postby karenzyj » Wed Jan 20, 2016 10:17 pm

You could collect data using multiple ph indicators, and if any produce numerous significant outliers, you'll know those are faulty.

If you want an easier way to determine accuracy, you could compare the values given by your ph indicators with those listed on this web page:

http://www.fda.gov/Food/FoodborneIllnes ... 122561.htm

This is from the U.S. Food and Drug Administration archive, so the data there should be scientifically proven and reliable.


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Re: ph indicators

Postby dfcoll » Thu Jan 21, 2016 4:11 am

Hi Harpeck,

That sounds like a really interesting experiment!

It might be a challenge deciding which indicator is "best" by the accuracy of the measurement. The pH indicators give you qualitative information (data that is not a number) of color. You then have to match that color to a known pH value using a quatitative measurement (one that gives you a number). Karenzyj gave an excellent link that you can use to match known pH to color. You could also use a pH meter to match solution color to number, but the tricky part is whether your eyes can tell the difference between the colors of solutions at pH 5.0 and 5.2 (for example). There might be a difference in color that your eyes cannot see, even though the indicator is changing. You might be able to use some kind of spectroscopy to measure the color change more precisely, but I'll have to leave that discussion to another expert.

You might compare whether the different food indicators change color noticeably over the same pH range, and determine that the one with the widest visible range is the "best". If you make a color chart (color versus pH) for your solutions, you should be able to tell over what pH range there is the most noticeable change.

Information on pH meters:

Example of a pH color chart:

Hope that helps! Let us know what you decide to do.

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Re: ph indicators

Postby Harpeck » Thu Jan 21, 2016 10:16 am

Thank you both for your inputs. I think I'm actually going to change it a little to make it a bit easier. I'm going to test which homemade pH indicator gives the closest results to a store bought pH strip.

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