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Determination method of water-soluble acid (acidity meter method)


This method is suitable for the determination of water-soluble acids in insulating oil and steam turbine oil

1. Summary of method

Mix and shake equal volumes of distilled water and test oil at 70~80°C, take its water extract, and measure its pH value with an acidity meter

2. instruments

⑴ PH meter

⑵ Separating funnel

⑶ Erlenmeyer flask

⑷ Pipette

⑸ beaker

⑹ volumetric flask

⑺ thermometer

⑻ Water bath

3. Reagents

⑴ Potassium hydrogen phthalate

⑵ potassium chloride

4. Preparations

⑴ Prepare potassium hydrogen phthalate standard solution: weigh potassium hydrogen phthalate that has been dried at 110-120°C in advance. Put it in a beaker, dissolve it with an appropriate amount of distilled water, transfer it into a volumetric flask, and dilute it to the mark with distilled water. The pH value of this solution is 3.97, which is used for the positioning of the acidity meter.

⑵ Glass electrode: soak in distilled water before use, and the soaking time must be more than 24 hours before use.

⑶ saturated potassium chloride solution

⑷ Zero point adjustment and positioning: adjust and position according to the instrument manual

5. Test steps

⑴ Measure the test oil, inject it into the Erlenmeyer flask, add an equal volume of pre-boiled distilled water, heat it to 70~80°C in a water bath, and shake it for 5 minutes

⑵ Pour the liquid in the Erlenmeyer flask into the separatory funnel, and after layering and cooling to room temperature, pour 30~40ml of water extract without oil into the 50ml beaker, and measure its pH value with a pH meter

6. Precision

The difference between the two results of the parallel determination should not exceed 0.05pH

Note: The pH value measured with a pH meter is about 0.2 higher than the result of visual colorimetric determination