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Author: Subject: Homemade Ph Indicator from purple cabbage
Hermes_Trismegistus
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[*] posted on 15-1-2004 at 18:14
Homemade Ph Indicator from purple cabbage


MAKING CABBAGE INDICATOR

INTRODUCTION:

Acid base indicators are chemicals that change color in the presence of different pH levels. These are usually larger organic molecules. Some, like that in purple cabbage, are natural.

You will be making an acid base indicator from purple cabbage. This indicator is a very good one with good color changes.
MATERIALS NEEDED:

Tea strainer
2 Glass quart jars with lids
1 Quart distilled water
Uncooked purple cabbage
Hotplate and pan

PROCEDURE:

Fill one jar with cabbage leaves that have been torn into small pieces.

Heat the distilled water to boiling, and fill the jar containing the pieces of cabbage with the hot water.

Allow the jar to stand until the water cools to room temperature.

Poor the cooled cabbage solution through the tea strainer into the second quart jar. Discard the cabbage leaves.

Store the cabbage indicator in a refrigerator until needed.

RESULTS:

The hot water dissolved the colored chemicals in the cabbage. These colored chemicals turn red when mixed with an acid, and green when mixed with a base. This indicator can be used to test for the presence of either an acid or a base.

Posted w/out permission from original author (labdad)




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[*] posted on 15-1-2004 at 18:21
Turmeric Base indicator


MAKING TURMERIC PAPER

INTRODUCTION:

Some indicator solutions and papers will indicate both an acid and a base, while others are specific to just one. In this lab you will be making a test paper that will indicate the presence of a base.
MATERIALS NEEDED:

Zip-lock plastic bag
Teaspoon
1/3 cup alcohol
1/4 teaspoon turmeric powder
Coffee filters
Cup
Cookie sheet
Quart bowl

PROCEDURE:

Fill a cup one-third full with alcohol.

Stir 1/4 teaspoon powdered turmeric into the alcohol.

Pour the solution into the quart bowl.

Dip one coffee filter at a time into the turmeric solution.

Place each wet filter on the cookie sheet and allow them to dry.

Cut the dry papers into strips about one-half inch by three inches.

Store the strips in a zip-lock plastic bag.

RESULTS:
Indicators are materials that have a specific color change. The dry turmeric paper is a bright yellow and is an indicator for a base. The color change is from yellow to red.

Reprinted without permission from LabDad




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[*] posted on 16-1-2004 at 13:39


Turmeric paper is also used for the detection of borates. Next question; Who wants to detect borates?
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[*] posted on 16-1-2004 at 14:38


In reactions where HCl and/or NH3 are used to acidify/neutralize etc... CuSO4 is a good pH indicator.

Once there is free HCl in the solution, it will form the deep green CuCl4 complex, is there free NH3 in the solution you'll get deep blue Cu(NH3)4. This is fairly sensitive and the color transition is very sharp.




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[*] posted on 16-1-2004 at 22:27


Iron(II) Sulphate is useful for detecting nitrates, this is called the 'brown ring' test.
Quote:
Iron(II) Sulphate is added to the cold solution to be tested, and concentrated sulphuric acid is added down the side of the test tube; in the presence of a nitrate a brown or black ring is formed at the junction of the two liquids. This test is unreliable in the presence of bromide or iodide (which also give coloured rings).

This is taken from "The Penguin Dictionary of Chemistry, 3rd Edition". The cabbage indicator will only last a few weeks in the fridge and then it will start to grow this blue mould (I don't know if this is different for anyone else). It would be interesting to know if there is a way to prolong its storage life.




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Saerynide
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[*] posted on 17-1-2004 at 00:11


Can paper strips be soaked in the cabbage juice and dried off for use as test strips?
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[*] posted on 17-1-2004 at 02:33


They probably could. Keep them away from light though, as many of these indicators are UV sensitive.



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[*] posted on 17-1-2004 at 06:57


I once tested blue Morning Glory flowers as a Ph test and they showed a relly big difference in color change. Use the dried flower petal (they turn purple when dried) and soak them in water, they color the water quickly and strong. Not many flower colors dissolve that well in water. It's purple when acidic, but turn green when basic. It is'nt stable in the basic form thou. I don't know the Ph-range, which is rather important, maybe someone with a Ph meter could check it out. Also I belive I saw a blue color just when it was about to change from purple to green.
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[*] posted on 17-1-2004 at 07:23


Seems a waste of such pretty flowers :D

So if they turn purple when acidic, and the dried flowers are also purple, what color is it when its neutral?
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[*] posted on 17-1-2004 at 07:43


Yes. That is what would like to know also. Therefore my suggestion that someone with a Ph-meter could check it out. Besides I belive that blue is the neutral color but it is a very narrow range. (wich is actually good). And you could collect the petals after they dried, so you could still get your seeds!.;)
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[*] posted on 18-1-2004 at 01:55


I just found quite an interesting page at About, Home and Garden pH Indicators

:)

[Edited on 18-1-2004 by ech310n]




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[*] posted on 18-1-2004 at 09:50
ech310n........sweet dude!


Red cabbage contains a pigment molecule called flavin (an anthocyanin). This water-soluble pigment is also found in apple skin, plums, poppies, cornflowers, and grapes. Very acidic solutions will turn anthocyanin a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the color it turns the anthocyanin pigments in red cabbage juice.

The color of the juice changes in response to changes in its hydrogen ion concentration. pH is the -log[H+]. Acids will donate hydrogen ions in an aqueous solution and have a low pH (pH < 7). Bases accept hydrogen ions and have a high pH (pH > 7).

Here is a table of approximate colors of red cabbage indicator solution at different pH's. If you wish, make your own chart, using chemicals of known pH.



pH------2------4 ------ 6 ------- 8 ------- 10-------------12
Color Red- Purple- Violet- Blue - Blue-Green - Greenish Yellow


[Edited on 18-1-2004 by Hermes_Trismegistus]




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[*] posted on 18-1-2004 at 11:00


whats the difference between purple and violet? I always used those to terms interchangebly.
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[*] posted on 18-1-2004 at 12:12


Violet is lighter, Purple is more grape juice....Violet is more of a pinkish purple.



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smile.gif posted on 28-5-2004 at 08:32


Purple is the color of dark blood (carboxylated blood).
Violet is the color you get when mixing pink and blue....like the Joker costume in Batman.
Thus purple is closer to red and violet is closer to blue....but indeed in the mean regio...hard to tell wich is which; like for turquoise....wich is green..no blue...euhhh
;);););)




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[*] posted on 19-7-2006 at 04:51


the flowers on the Hydrangea also change color according to soil conditions and ph, perhaps an extract could be had that would provide another suitable indicator?



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[*] posted on 19-7-2006 at 22:33


It works with pretty much any dark purple flower. I've used pansies and violas (viola tricolor), and the color range was very similar to red cabbage.



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[*] posted on 10-8-2006 at 17:52


For whatever method you use to make the pH indicator, I would advise you to test the strips using various substances with a known pH for accuracy reasons. When I perform experiments, I maintain my lab meticulously to eliminate any impurities and other variables.

[Edited on 11-8-2006 by cranium]




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[*] posted on 11-8-2006 at 05:08


"When I perform experiments, I maintain my lab meticulously to eliminate any impurities and other variables."
I'm intrigued; the dyes from plants etc are susceptible to atmospheric oxidation. How do you keep air out of the experiments? I know you can do it if you have a glove box but that's a bit much for most home labs.
I'd also like to know where you get ultra pure water from.

[Edited on 11-8-2006 by unionised]
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[*] posted on 11-8-2006 at 13:20


I do not make my own pH indicator. I usually use pH paper, so use a little logic to figure out what I mean.



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[*] posted on 19-8-2006 at 03:58


As far as I can tell, the rules of logic will not answer my question about keeping air out of experiments nor will they infrom me about how you prepare ultra pure water.
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