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Self made acid/base indicators, PH indicators

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A lot of plants with colors other than green are usable as a PH indicators. Some of the most commonly known ones are: The litmus paper is used in labs around the world to test whether a solution is acidic or basic. The advantage of litmus is that it can be stored over many years and remains usable.
Litmus PH indicator
below ph 4.5above ph 8.5

Red cabbage is cheap, very color intensive and can actually indicate the PH of a solution in more find grained steps. The problem is it works best with fresh cabbage and the extract is only usable for a couple of weeks. It is however still a very useful "home made" PH indicator and it's a nice experiment for a science class in school. To make red cabbage extract you cut a few leaves of red cabbage into small slices or you can put them into a mixer.


red cabbage leaves


Add a 50-70% alcohol water solution and let it sit for about 15 minutes. I recommend to use real ethanol and not isopropyl alcohol if you do this experiment with children where it is difficult to avoid that some get in contact with the alcohol. Both ethanol and isopropyl-alcohol are toxic but ethanol is less toxic to humans. Isopropyl causes kidney damages even if it is just used externally over a longer period of time. Short exposure of a hand or the inhalation of the vapor for a few minutes is supposedly not dangerous but ethanol is for sure less dangerous.


red cabbage extraction process


Separate the cabbage from the now dark colored alcohol solution by pressing it through a cheese cloth and fill the red cabbage indicator solution into a small bottle for storage.


red cabbage extract PH indicator


To test the PH of any liquid just add a few drops of the red cabbage extract and then compare the color with the following table.
Red cabbage extract PH indicator
ph 0-1 ph 2 ph 4 ph 5-8 ph 9 ph 10 ph 11-14

Turmeric and Radish as PH indicators

Red cabbage is a very good PH indicator but is looses its ability to indicated the PH over a couple of weeks or month depending on how you store the solution. More stable PH indicators that can easily made at home are: Radish peels are stable for many month and turmeric continues to work for many years. Radish is similar to red cabbage in the sense that it can indicate the PH in many fine grained steps where as turmeric has just two colors similar to litmus.

The best way to store turmeric over longer periods is to store it as powder. To use it just mix a bit of powder with water.
Turmeric PH indicator
below ph 7.4above ph 8.6

Radish extract is produced in the same way as red cabbage extract. Just peel the red skin off several radishes and then extract the dye using an alcohol water solution.


radish



radish skin peeled



radish peels extraction with alcohol and water


radish extract PH indicator


Radish extract changes its color according to the PH as shown in the below table.
Radish extract PH indicator
ph 0-2 ph 3 ph 4-7 ph 8-9 ph 10 ph 11-14

References


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