Preparation method of two iron-hydrochloric acid-alkali indicators

Abstract

The acid-base indicator has important application in the fields of chemical industry, food, medicine and the like, so that a plurality of inorganic and organic acid-base indicators are invented by people. The invention prepares two novel acid-base indicators with similar processes and properties. The method specifically comprises the following steps: firstly, dissolving chitosan by using an aqueous solution of lactic acid, then adding a ferrous sulfate solution into the solution, and dialyzing and standing to obtain a solution containing ferrous ions. Adding potassium ferricyanide into the solution to obtain an indicator A; adding ammonium thiocyanate and a small amount of sulfuric acid into the indicator A to obtain an indicator B; the two indicators are blue and faint yellow when the pH value is 9-10 or above. Wherein the indicator B can still turn blue after being added into the acid solution again.

Description

Technical Field

[0001] This invention relates to the fields of chemical engineering and food processing, specifically to two methods for preparing iron salt acid-base indicators with similar processes. Background Technology

[0002] Potassium ferricyanide is an inorganic compound with the chemical formula K3[Fe(CN)6], commonly known as ferricyanide, and a molecular weight of 329.24. It appears as red crystals, soluble in water and acetone, slightly soluble in ethanol, and insoluble in methyl acetate. Its aqueous solution exhibits a yellow-green fluorescence and contains the ferricyanide complex ion [Fe(CN)6]3-. Its aqueous solution gradually decomposes during storage and is easily decomposed by light and alkali. It forms a deep blue precipitate (Thun's blue) upon contact with ferrous salts. Potassium ferricyanide is mainly used in the photographic paper, pigment, leather, pharmaceutical, fertilizer, electroplating, and papermaking industries.

[0003] Lactic acid, with the chemical formula C3H6O3, contains a hydroxyl group and belongs to the α-hydroxy acid family. The pure product is a colorless, odorless, and hygroscopic liquid. Its relative density is 1.2060 (25 / 4℃). Its melting point is 18℃. Its boiling point is 122℃ (2kPa). It is miscible with water, ethanol, and glycerol; its aqueous solution is acidic, and it produces lactate ions (CH3CH(OH)COO-) in aqueous solution. It is insoluble in chloroform, carbon disulfide, and petroleum ether. Because lactic acid molecules contain both hydroxyl and carboxyl groups, they can undergo esterification under certain conditions.

[0004] Chitosan is a product of the deacetylation of chitin. Chitin, a natural polysaccharide, is abundant in the shells of shrimp, crabs, insects, and mollusks. Chitin is widely distributed in nature and is the second largest natural polymer after cellulose, making it a recyclable resource. Chitin and chitosan have similar chemical structures, thus the production of chitosan from chitin holds great promise. Chitosan contains free amino groups and is the only basic polysaccharide among natural polysaccharides. Chitosan possesses many unique properties, including biodegradability and cell affinity, and exhibits various physiological functions such as biocompatibility, non-toxicity, and antibacterial properties. It has wide applications in food, environmental protection, cosmetics, antibacterial applications, agriculture, medicine, and pharmaceuticals.

[0005] Potassium thiocyanate (KSCN) is an inorganic compound, a colorless to white crystalline solid. It is readily soluble in water and cools due to the large amount of heat it absorbs. It is also soluble in alcohol and acetone. As a chemical reagent, it is a common indicator of iron ions (Fe³⁺). SCN⁻ coordinates with Fe³⁺ to form [Fe(SCN)n]³⁻n, which turns the solution blood red upon addition. It is also used to detect copper and silver. In industrial applications, it is mainly used in the synthesis of resins, pesticides, thiourea, and mustard oil. It can also be used as a refrigerant and photographic thickener. Summary of the Invention

[0006] Acid-base indicators have important applications in chemical, food, and pharmaceutical fields, leading to the invention of numerous inorganic and organic acid-base indicators. This invention produces two novel acid-base indicators with similar processes and properties. Specifically, chitosan is first dissolved in an aqueous solution of lactic acid. Then, a ferrous sulfate solution is added, followed by dialysis and standing to obtain a solution containing ferrous ions. Adding potassium ferricyanide to this solution yields indicator A. Its aqueous solution is blue, gradually fading to pale yellow upon contact with alkali, with the color change occurring at approximately pH 9-10. Adding acid does not restore the blue color.

[0007] Adding potassium thiocyanate and a small amount of sulfuric acid to indicator A yields indicator B. Its aqueous solution is blue; adding acid increases the acidity, deepening the blue color. In the presence of alkali, it gradually fades to pale yellow, with the color change occurring around pH 9-10. Adding more acid will restore the blue color, but it is not suitable for repeated use.

[0008] Specific Plan

[0009] S1. Prepare a lactic acid aqueous solution by adding 4-6 ml of lactic acid per 100 ml of solution;

[0010] S2. Add chitosan powder, at a rate of 2-4 grams per 100 ml. Stir continuously until the chitosan dissolves into a solution. S3. Prepare a ferrous sulfate solution, adding 2-4 grams of ferrous sulfate per 100 ml of the solution. Immediately add the ferrous sulfate solution to the chitosan lactic acid solution at a 1:1 volume ratio to prevent oxidation.

[0011] S4. After adding chitosan, it precipitates out. Let it stand open for at least 1 hour to allow the reaction to complete, then filter out the precipitated chitosan.

[0012] S5. Dispense the obtained filtrate into dialysis bags, 20-30 ml per bag. Immerse the dialysis bags in a beaker containing 100 ml of pure water and dialyze for at least 10 hours. Then remove the dialysis bags and collect the remaining aqueous solution.

[0013] S6. If this solution is left exposed for about a week, you can observe that its color gradually turns light green and finally turns orange.

[0014] S7. Add 0.1-0.2 grams of potassium ferricyanide powder to each cup of this solution. The solution turns blue, indicating the presence of indicator A. If a precipitate forms, remove it by filtration.

[0015] S8. Add 0.1-0.2 g of potassium ferricyanide powder, 0.1-0.2 g of potassium thiocyanate powder, and 2-3 ml of 10% sulfuric acid solution to each cup of this solution. Initially, it is bluish-green, but after standing for several hours to a day, it stabilizes into a blue color, thus obtaining indicator B. If there is a precipitate, remove it by filtration.

[0016] Note: Steps S7 and S8 will produce a small amount of irritating gas; therefore, they should be performed in a well-ventilated area and then stored in a sealed container. Indicator B's blue color will slowly fade under light and oxygen conditions, so it should also be protected from light and oxygen and should not be stored for extended periods. A small amount of lactic acid can be added to adjust the pH to slightly acidic to maintain the color.

[0017] The above processes and proportions are for illustrative purposes only. In actual applications, appropriate adjustments may be made as needed, and these adjustments should also be included within the scope of protection of this invention.

Claims

1. Two ferric acid-base indicators have the following characteristics: Indicator A has a blue aqueous solution that turns pale yellow upon contact with an alkali, with the color change occurring at around pH 9-10. Adding acid does not restore the blue color. Indicator B has a blue aqueous solution that turns pale yellow upon contact with an alkali, with the color change occurring at around pH 9-10. Adding acid restores the blue color.

2. A method for preparing two types of iron salt acid-base indicators, characterized in that, Chitosan was dissolved in lactic acid to prepare a chitosan solution. Ferrous sulfate solution was added, and after dialysis and standing, a new solution was obtained. Adding potassium ferricyanide powder to this solution yielded indicator A; adding potassium ferricyanide powder, ammonium thiocyanate powder, and sulfuric acid solution to this solution yielded indicator B.

3. The preparation methods for the above two iron salt acid-base indicators specifically include the following steps: S1. Prepare a lactic acid aqueous solution by adding 4-6 ml of lactic acid per 100 ml of solution; S2. Add the chitosan powder to it. The mass is 2-4 grams per 100 milliliters. Stir continuously until the chitosan dissolves into a solution; S3. Prepare a ferrous sulfate solution by adding 2-4 grams of ferrous sulfate per 100 ml of solution. Then immediately add the ferrous sulfate solution to the chitosan lactic acid solution at a 1:1 volume ratio to prevent oxidation. S4. Let it stand open for more than 1 hour to allow the reaction to be complete, and then filter out the precipitated chitosan. S5. Dispense the obtained filtrate into dialysis bags, 20-30 ml per bag. Immerse the dialysis bags in a beaker containing 100 ml of pure water and dialyze for at least 10 hours. Then remove the dialysis bags and collect the remaining aqueous solution. S6. Leave this solution exposed to the air for about a week; S7. Add 0.1-0.2 grams of potassium ferricyanide powder to each cup of this solution to obtain indicator A; S8. Add 0.1-0.2 g of potassium ferricyanide powder, 0.1-0.2 g of ammonium thiocyanate powder, and 2-3 ml of 10% sulfuric acid solution to each cup of this solution. Let it stand to stabilize the color, and you will get indicator B.

4. The above process and proportions are for illustrative purposes only. In actual applications, appropriate adjustments may be made as needed, and these adjustments should also be included within the scope of protection of this invention.