The pH value (pH value) of natural water is mostly in the range of 6 to 9, which is also the pH control range in China's wastewater discharge standards. pH value is one of the commonly used and most important test ranges in water chemistry. Since the pH value is affected by the water temperature, the measurement should be carried out at the specified temperature, or corrected temperature. The glass electrode method and the colorimetric method are commonly used to determine pH. The glass electrode method is often used in laboratories because the glass electrode is basically free from the interference of chromaticity, turbidity, colloidal substances, oxidizing agents, reducing agents and salinity.
Operation method
glass electrode method
Principle
The glass electrode is used as the indicator electrode and the saturated calomel electrode is used as the reference electrode to form a cell. Under the ideal conditions of 25℃, the hydrogen ion activity changes by 10 times, which causes the electric potential to shift by 59.16mV, and the PH value is measured according to the amount of change in the electric potential. The effect of temperature on the electrode is corrected by a temperature compensation device on the PH meter. In order to improve the accuracy of the measurement, the PH of the standard buffer used for calibration should be close to the PH value of the water sample.
Materials and Instruments
Water samples Move I. Reagent Preparation Caveat 1. The glass electrode should be soaked in distilled water for more than 24 h before use. After use, rinse well and place in a protective cap containing 3 mol/l KCl to keep the electrode bulb moist. Avoid soaking the glass electrode in distilled water for a long time. 2. When the glass electrode bulb is contaminated, use dilute hydrochloric acid to dissolve the inorganic salt dirt, use acetone to remove the oil (but not anhydrous ethanol) and then use pure water to clean it, and then put it into the water to soak for one day and night and then use it again. 3. The external reference solution of the composite electrode is 3 mol/L KCl solution, which can be added from the small hole of the electrode. 4. The lead end (plug) of the electrode must be kept clean and dry, and the output end must be prevented from short-circuiting, otherwise the measurement results will be inaccurate or invalid. 5. after long-term use, such as found that the electrode of the percentage of the theoretical slope is slightly reduced, then the electrode can be soaked in 4% HF at the lower end of 3-5 seconds, washed with distilled water, and then soaked in 0.1 mol / l HCl solution for a few hours, rinsed with deionized water, so that it is new again. 6. Determination of pH value of water samples should preferably be carried out in the field, otherwise, the sample should be kept at 0 ~ 4 ℃ after sampling, and the determination should be carried out within 6 h after sampling . 7. In order to prevent the dissolution of carbon dioxide in the air or the escape of carbon dioxide in the water sample, the water sample bottle should not be opened in advance before the determination of the cork. For more product details, please visit Aladdin Scientific website.
Potassium hydrogen phthalate Potassium dihydrogen phosphate Disodium hydrogen phosphate Sodium tetraborate
Composite Glass Electrodes Polyethylene Beakers PTFE Beakers Magnetic Stirrers pH Meters Ion Activity Meters
1. Standard buffer solution pH 4.008: Prepared as bagged potassium hydrogen o-phthalate.
2. Standard buffer solution pH 6.865: Prepared as bagged potassium dihydrogen phosphate and disodium hydrogen phosphate.
3. Standard buffer solution pH 9.180: Prepared as bagged sodium tetraborate.
II. Experimental steps
1. Calibration instruments
Adopt two-point calibration method, the first standard solution and water samples to the same temperature (the temperature difference between the two should be within ± 1 ℃), record the measurement temperature, and the instrument temperature compensation knob adjusted to the temperature; neutral standard buffer solution positioning, close to the water samples of the standard buffer solution adjust the slope, and repeated debugging so that the difference between the indicated value and the standard value is less than 0.1 PH. (Note: the electrode in the alternately inserted into the standard buffer solution to be used) (Note: The electrode should be rinsed with distilled water and dried with filter paper when inserting standard buffer solution alternately).2. Measurement of water samples
First rinse the electrode with distilled water, then rinse it with the water sample to be measured, immerse the electrode in the water sample, stir or shake carefully to make it uniform, leave it to stand, and then record the PH value after the readings are stabilized.