pH Measurement of Aqueous Solutions

The REX PH500T pH Meter allows quick and simple determinations of the pH of aqueous solutions with calibration reminder setting and verification reminder setting.

Aqueous solutions are used in numerous lubricating applications, such as metal working fluids and coolants. If the pH of these solutions is not correct, metals in the system may corrode, the solutions may oxidize or degrade and biological growth may be accelerated. This test determines the pH of aqueous solutions using a glass electrode.

1.Standard Reference

ASTM E70- 19 Standard Test Method for pH of Aqueous Solutions With the Glass Electrode

This test method specifies the apparatus and procedures for the electrometric measurement of pH values of aqueous solutions with the glass electrode. It does not deal with the manner in which the solutions are prepared. pH measurements of good precision can be made in aqueous solutions containing high concentrations of electrolytes or water-soluble organic compounds, or both. It should be understood, however, that pH measurements in such solutions are only a semiquantitative indication of hydrogen ion concentration or activity.

2.The Principle

pH—defined formally as the negative logarithm to the base 10 of the conventional hydrogen ion activity.

pH measurements of good precision can be made in aqueous solutions containing high concentrations of electrolytes or water-soluble organic compounds, or both. It should be understood, however, that pH measurements in such solutions are only a semiquantitative indication of hydrogen ion concentration or activity. The measured pH will yield an accurate result for these quantities only when the composition of the medium matches approximately that of the standard reference solutions. In general, this test method will not give an accurate measure of hydrogen ion activity unless the pH lies between 2 and 12 and the concentration of neither electrolytes nor nonelectrolytes exceeds 0.1 mol/L (M).

3.Recommended Configuration

PH500T pH meter

The pH meter is calibrated, the electrode is immersed in the aqueous sample solution and the pH is measured and reported to 0.01 pH units.

 If only an occasional pH determination is made, standardize the assembly each time it is used. In a long series of measurements, supplement initial and final standardizations by a check at intervals of l h, or longer if little or no change is found between successive standardizations.

50. Multi-reading feature allows auto-read, timed-read and continuous-read. 
50. Automatic/Manual temperature compensation ensures accurate results.
50. Calibration reminder setting and verification reminder setting ensures standardization.
50. Automatic electrode diagnosis with pH slope and offset display.

Reference Electrodes and Glass Electrodes

The design of the electrode shall permit a fresh liquid junction between the solution of potassium chloride and the buffer or test solution to be formed for each test and shall allow traces of solution to be readily removed by washing.

The silver-silver chloride electrode also is used widely as a reference electrode and has replaced the mercury containing calomel electrode.

Other reference electrodes of constant potential may be used. Combination pH electrodes with or without integrated temperature sensor are permitted for use with this test method.

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