Zhengzhou Weier-PH reagent production, use and application range
August 02 12:47:48, 2025
For many years, two primary methods have been used to determine pH: pH test paper and pH meters. While the former is low-cost and easy to use, it suffers from poor accuracy, large margin of error, and inability to detect weak buffer solutions or low-concentration acids and bases. On the other hand, pH meters offer high precision but are expensive, require complex operation, and often demand controlled environments, making them less convenient for everyday use.
The introduction of pH reagents has significantly improved this situation. These reagents simplify the process, reduce costs, and provide reliable results. To use a pH reagent, simply add 3–4 drops into 50 mL of the test solution, or dilute the sample by half and add 1–2 drops of the reagent. By comparing the resulting color with a standard color chart, you can accurately determine the pH of the solution.
When preparing pH reagents at home, it's important to note that they cannot provide exact numerical values. They typically measure only one type of acid, and the pH readings may vary depending on concentration, temperature, and vapor pressure. However, these indicators are still valuable for general testing.
Several common pH indicators are prepared as follows:
- **Sodium diphenylamine sulfonate**: Dissolve 0.2 g in 100 mL water.
- **Diphenyl hydrazine**: Dissolve 1 g in 100 mL ethanol.
- **Dithizone**: Dissolve 50 mg in 100 mL ethanol.
- **Litmus**: Soak 10 g of litmus powder in 40 mL ethanol, reflux for an hour, filter, and repeat twice. Wash with water and ethanol, then boil in 50 mL water. The color change range is pH 4.5 to 8.0 (red to blue).
- **Cresol red**: Dissolve 0.1 g in 5.3 mL of 0.05 mol/L NaOH, then dilute to 100 mL. Color change: pH 7.2 to 8.8 (yellow to red).
- **Methyl red**: Dissolve 0.1 g in 7.4 mL of 0.05 mol/L NaOH, then dilute to 200 mL. Color change: pH 4.2 to 6.3 (red to yellow).
- **Methyl orange**: Dissolve 0.1 g in 100 mL water. Color change: pH 3.2 to 4.4 (red to yellow).
- **Phenolphthalein**: Dissolve 1 g in 100 mL ethanol. Color change: pH 8.3 to 10.0 (colorless to red).
- **Starch**: Mix 0.5 g of soluble starch with 5 mL water, then slowly add to boiling water. Boil for 2 minutes, cool, and filter. Used fresh for best results.
- **Thymol blue**: Dissolve 0.1 g in 4.3 mL of 0.05 mol/L NaOH, then dilute to 200 mL. Color change: pH 1.2–2.8 (red to yellow), and pH 8.0–9.6 (yellow to purple-blue).
These reagents are widely used in various fields such as aquaculture, wastewater treatment, laboratories, boiler water, ionized water, pharmaceuticals, and more. They are highly accurate, user-friendly, and cost-effective. A 10 mL bottle can be used up to 150 times, far exceeding the limited usage of pH test paper. Their application ranges from educational demonstrations to quality control in drinking water systems and industrial settings.