Phenolphthalein represents organic compound- indicator of acid and alkaline environment. Can be used as an industrial technical dye. Until recently, it was widely used in pharmacology due to its pronounced laxative properties and was sold under the brand name “purgen”.
Production and chemical properties of phenolphthalein
The synthesis of phenolphthalein occurs through the joint process of condensation of phthalic anhydride and phenol. The initial reaction temperature is 100 - 110 degrees. Can act as a catalyst for the process sulfuric acid high concentration or technical zinc chloride (zinc chloride). Phenolphthalein, heated with sulfuric acid, allows for the reverse reaction to produce phenol.
Appearance and physical properties of phenolphthalein
Phenolphthalein has a visual crystalline structure that is predominantly diamond-shaped. It dissolves poorly in water and contains excess sediment. Soluble in diethyl ether and alcohol. To indicate the medium, in most cases it is used as an alcohol solution. Initial solid has medium density 1.3 g per 1 cm3.
Applications of phenolphthalein
Today, the main use of phenolphthalein is associated with the indication of an alkaline environment on specialized products, in particular, medical purposes. In industry and analytical chemistry the drug is used to determine the total acidity of alcohols and alcohol solutions, calorimetric analysis of acidity levels, and so on. Phenolphthalein is usually used as a dye for lead, magnesium, zinc, and so on. In medicine, the use of the drug is irrelevant, as it is due to a strong cumulative effect and the possibility of damage to human kidney tissue with long-term use. In addition, when administered orally, properties similar to carcinogens were observed. However, complete refusal medicine has not been used in medical practice, but use should be carried out with great caution.
Preparation of solution for indication
Phenolphthalein solution For most controlled surfaces it is prepared at a concentration of 1%. For this, 1 gram of initial crystalline substance dissolve in 100 ml of ethyl alcohol. The shelf life of the working solution is one month. Store the solution in the refrigerator.
Methods of using the working solution
- Apply 2-3 drops of solution to the surface to be tested.
- The swab is moistened with the solution and the surface being tested is lubricated.
- The instrument to be tested for the presence of an alkaline environment is immersed in the solution.
- 2 - 3 drops of solution are added to a controlled liquid environment.
The choice of testing method depends on the specifics and size of the controlled environment.
Reaction of the working solution to acidic and alkaline environments
- Strongly acidic environment. Indicator color: orange.
- Slightly acidic environment. Indicator color: colorless.
- Neutral environment. Indicator color: colorless.
- Alkaline environment. Indicator color: pink.
- Highly alkaline environment. Indicator color: colorless.
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Indicators that have different colors in acidic and alkaline environments are called two-color (litmus, methyl orange). The color of the indicator in an alkaline medium is crimson. ELECTROLYTES). However, in a highly alkaline environment, phenolphthalein becomes discolored again! This happens because in an acidic and alkaline environment the indicator molecules have different structures.
Several hundred acid-base indicators are known, artificially synthesized since the mid-19th century. You can get acquainted with some of them in the school chemistry laboratory. In order to check this, you need to prepare a diluted solution of brilliant green: pour a few milliliters of water into a test tube and add one or two drops of the pharmaceutical preparation to it.
However, most often in laboratory practice a universal pH indicator is used - a mixture of several acid-base indicators. When it dries, the pH indicator is ready. Let's try its action. To do this, let’s dip our one pH indicator into a solution of soda ash, which is probably available on the farm (or sold in hardware stores). You can also use ammonia. Our pH indicator will react to the solution and change its color to blue-green (after all, solutions of soda ash and ammonia give an alkaline environment!).
Application in medicine
Soda ash (or sodium carbonate) – Na2CO3 – is a white powder used in household cleaning and washing as a strong detergent. Persol. This complex substance is salt, the main component which is bound sodium carbonate and hydrogen peroxide in one molecule 2Na2CO3*3H2O2. When heated, this substance easily decomposes, releasing oxygen and turning into sodium carbonate (regular washing soda Na2CO3) and water. Persol is good because it practically does not spoil the paint.
Finally, in concentrated sulfuric acid, a red color appears again, although not as intense
In soda ash, sodium atoms replaced all the hydrogen atoms, but in baking soda, “there weren’t enough sodium atoms.” Baking soda It is much less soluble in water than soda ash (washing soda), and, unlike the latter, it gives a very weak alkaline reaction. METHOD 2: In exactly the same way, you can prepare a pH indicator from mulberry juice.
Onion broth can serve as an indicator, but a pH indicator made from it has less pronounced colors and is not particularly indicative. METHOD 3: How to make a pH indicator from juice chokeberry.
The violet color of juices is given by so-called anthocyanin dyes, which have indicator properties. In the presence of acids they are purple, and in a neutral or alkaline environment they are blue. If you dissolve a few drops of chokeberry juice in a glass with a soda solution, it will turn blue.
This happens due to the formation of another colorless form of the indicator - in the form of a triply charged anion
4 METHOD How to make a pH indicator from cauliflower. All resources in the Collection are intended only for non-commercial use in the educational system Russian Federation. For others, falling into acid is a failure, But he will endure it without sighing, without crying. But in alkalis phenolphthalein will not have life, but pure raspberries!
Properties. White or slightly yellowish fine-crystalline powder, odorless and tasteless. Almost insoluble in water, soluble in alcohol (1:12). INDICATORS (from Latin indicator - pointer) - substances that allow you to monitor the composition of the medium or the flow of chemical reaction. An example is the common indicator phenolphthalein, which was previously also used as a laxative under the name purgen.
Our pH indicator will turn purple if placed in an acidic environment (such as vinegar or citric acid). Some of the most common are acid-base indicators, which change color depending on the acidity of the solution.