Homemade plant acid-base indicator
Wash the petals, leaves, peels, etc. of some fresh plants with clean water, then put them into a mortar and grind them with a pestle. Mash it, add 1 to 2 ml of alcohol (depending on the number of petals and other plants), soak for about 10 minutes according to the requirements for preparing a concentrated solution, and pound a few more times
times, dissolve it, add 2 ml of distilled water to dilute it, and finally wrap it with clean gauze to squeeze out the juice. If the juice is turbid, use a funnel to filter and remove the residue until it is clear. At this time, the clear solution can be used as an indicator
Plant acids and bases Test of the discoloration range of the indicator
(1) Test of the feasibility of the plant acid-base indicator
In each experiment, 1 to 3 kinds of plant flowers, stems, leaves, and roots were taken Or fruits were used to prepare plant indicators according to the above method. Then
drop some dilute hydrochloric acid (pH=2) and dilute sodium hydroxide (pH=12) solutions into the holes of the white drip plate, and then
respectively Add three drops of the alcohol solution of the prepared plant pigment indicator, observe its color change, and compare it with the original color in the third test tube to measure the pH value of the original juice. After good records, we came to the conclusion: It is feasible to use the indicator as an indicator if it changes color obviously when encountering acid or alkali solution, but the opposite is not possible. Then select plants with obvious discoloration and good feasibility for the next round of tests
Natural pH indicators can be selected from sugar radish, blueberry, carrot, cherry, delphinium petals, geranium petals, grapes, horse chestnuts, etc. Extracted from tree leaves, hydrangeas, onions, morning glory petals, primrose, poppy petals, purple peonies, red cabbage, carrots, rhubarb, rose petals, strawberries, thyme, and turmeric.
The color of morning glory is similar to that of purple litmus. It is red under acidic conditions, purple under neutral conditions, and blue under alkaline conditions.
Purple cabbage turns red when exposed to acid and turns blue when exposed to alkali.
The skin of dragon fruit turns colorless when exposed to acid and turns yellow when exposed to alkali.
Extended information:
The indicator used for acid-base titration is called an acid-base indicator. It is a type of organic weak acid or organic weak base with a relatively complex structure. They can be partially ionized into indicator ions and hydrogen ions (or hydroxide ions) in solution, and due to structural changes, their molecules and ions have Different colors, thus showing different colors in solutions with different pH.
Commonly used acid-base indicators mainly include the following four categories:
1. Nitrophenols? This is a type of significantly acidic indicator, such as p-nitrophenol wait.
2. Phenolphthaleins include phenolphthalein, thymolphthalein and α-naphtholphthalein, which are all organic weak acids.
3. Sulfonated phenolphthaleins include phenol red, cresol red, bromophenol blue, thymol blue, etc. They are all organic weak acids.
4. Azo compounds include methyl orange, neutral red, etc. They are all amphoteric indicators and can be used for both acidic and basic dissociation.