Zhengzhou Weier-PH reagent production, use and application range
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August 02 12:35:53, 2025
For many years, two common methods have been used to determine the pH of a solution: pH test paper and pH meters. However, each has its limitations. pH test paper is inexpensive but lacks accuracy, often leading to significant errors in results. It is especially ineffective for detecting weak buffer solutions or low-concentration acid-base solutions. On the other hand, pH meters provide more accurate readings, but they are costly, require careful handling, and are not always convenient for field use. To address these issues, pH reagents have emerged as a practical alternative.
pH reagents offer a simplified, cost-effective, and reliable method for measuring pH. They eliminate the need for complex instruments and reduce testing costs significantly. The procedure is straightforward: add 3–4 drops of the reagent into 50 mL of the test solution, or adjust the volume of the sample and add 1–2 drops accordingly. By comparing the resulting color with a standard color chart, the pH value can be easily determined. When preparing the reagent at home, however, it may not yield precise numerical values, and the results can vary depending on factors such as concentration, temperature, and vapor pressure.
Various indicators can be prepared using different compounds. For example, sodium diphenylamine sulfonate (0.2 g in 100 mL water) changes color from blue to violet. Diphenyl hydrazine (1 g in 100 mL ethanol) is another useful indicator. Dithizone (50 mg in 100 mL ethanol) is commonly used in metal detection. Litmus (10 g in 40 mL ethanol, then treated twice) changes from red to blue between pH 4.5 and 8.0. Cresol red (0.1 g in 5.3 mL of 0.05 mol/L NaOH, diluted to 100 mL) shifts from yellow to red between pH 7.2 and 8.8. A mixture of cresol red and thymol blue provides a broader range of color change.
Methyl red (0.1 g in 7.4 mL of 0.05 mol/L NaOH, diluted to 200 mL) works well between pH 4.2 and 6.3. Methyl red-methylene blue and methyl red-bromocresol green mixtures are also widely used in titrations. Methyl orange (0.1 g in 100 mL water) changes from red to yellow between pH 3.2 and 4.4. Similarly, xylene blue FF and methyl orange can be combined for better accuracy.
Other indicators include phenolphthalein (1 g in 100 mL ethanol), which turns from colorless to red between pH 8.3 and 10.0, and starch (0.5 g in 100 mL boiling water), used in iodine titrations. Bromophenol blue (0.1 g in 3 mL of 0.05 mol/L NaOH, diluted to 200 mL) changes from yellow to blue-green between pH 2.8 and 4.6. Thymol blue (0.1 g in 4.3 mL of 0.05 mol/L NaOH, diluted to 200 mL) exhibits two color transitions: red to yellow (pH 1.2–2.8) and yellow to purple-blue (pH 8.0–9.6).
These pH reagents are highly accurate, easy to use, and portable. Each 10 mL bottle can be used up to 150 times, far exceeding the performance of traditional pH test papers, which typically last less than 90 times. They are suitable for a wide range of applications, including aquaculture, wastewater treatment, laboratory analysis, boiler water monitoring, and even educational demonstrations. Their versatility and affordability make them an excellent choice for both professionals and students.