The acidity meter is what we usually call the pH meter. The acidity meter mainly measures the pH value of the aqueous solution by measuring the principle of the electromotive force of the battery. Conversely, pH meters also measure electrode potential.
The principle of pH meter
To measure the pH value with a pH meter, insert a pair of working electrodes into the solution to be tested, one is a reference electrode with a known and stable electrode potential (usually a calomel electrode), and the other is a electrode whose potential varies with the ionization of the solution. The indicator electrode (usually broken glass electrode) that changes due to concentration changes forms a primary battery and is connected to a precision potentiometer to measure the electromotive force of the battery. Since the pH value of the solution to be tested is different, the electromotive force generated is also different. Therefore, the pH value of the solution can be measured by measuring the electromotive force of the solution.
In order to save the procedure of converting electromotive force into pH value, the acidity meter directly displays the measured electromotive force of the battery on the electric dial with a p scale. On the same day, the instrument is also equipped with a positioning regulator. When measuring, first use p9 standard buffer solution , By positioning the regulator 11l so that the pointer is just about to point at its pH value. In this way, when measuring the solution to be tested, the pointer directly indicates the pH value of the solution to be tested. Usually, the previous step is called positioning, and the latter step is called measurement.
How to use the acidity meter
(1) Measuring the pH value
1. Calibration of pH meter
(1) Check whether the indicator pointer is at 1.0, otherwise use the pointer zero adjustment screw to adjust.
(2) Turn on the power, press the power switch, and then press the pH button. Preheat the instrument for 30 minutes. (3) Adjust the temperature compensation regulator to the temperature of the solution to be tested, and connect the electrode. Turn the gear switch to the "6" position (at this time, the measuring range of the indicator is pH6~8), adjust the zero point adjustment knob so that the pointer points at 1.0 (that is, pH-7.0), (5) turn the gear switch to "correction ” position, adjust the 1J correction knob to make the pointer point to the full scale of 2.0.
(6) Repeat steps (4) and (5) to check the reproducibility of the pointer at 1.0 and 2.0. When the instrument is stable, the calibration is over. After that, the zero adjustment knob and the calibration knob cannot be moved again.
2. Positioning of the acidity meter
Insert the connected electrode into the pH standard buffer solution, press the reading button, adjust the positioning knob so that the pointer points to the pH scale of the standard buffer solution (the sum of the value indexed by the step switch and the index pointer of the indicator), and stir Solution, adjust the positioning knob repeatedly until the pointer is stable. Then release the reading button, the positioning is completed, and the positioning knob cannot be moved after that.
3. Measurement of acidity meter
Take out the electrode, rinse it with distilled water and gently blot the moisture on the surface of the electrode with filter paper, then include it in the solution to be tested, turn the step switch to the measured range, press the reading button, the index value and indication of the step switch The sum of the values indicated by the hands of the meter is the pH value of the solution to be tested.
4. Precautions for acidity meter
(l) The glass electrode is easy to break, so be careful not to collide with it when using it.
(2) The broken glass electrode should be soaked in distilled water for more than 24 hours before use.
(3) The calomel electrode should be replenished with saturated KCl solution in time to maintain a sufficient hydraulic pressure difference.
(4) Do not soak the calomel electrode for a long time.
(2) Measuring the electromotive force of the battery
(l) Connect the two poles of the battery to be tested to the corresponding electrode connectors of the instrument, and press the +mV button to preheat the instrument for 30 minutes.
(2) Adjust the temperature compensation regulator to the temperature of the solution to be tested.
(3) Turn the split switch to the 0" position, adjust the zero adjustment knob so that the pointer points to 1.0, then turn the split start to the "correction" position, adjust the correction knob to make the pointer full scale (0- 2.0 scale).
(4) Turn the gear switch to the "0" position, loosen the screw of the negative pole jack, pull out the negative pole plug, then connect the reading button, adjust the positioning knob so that the pointer points to "0", after adjustment , release the reading button, and the pointer returns to 1.0. Then insert the negative plug, and tighten the small screw on the jack.
(5) Insert the electrode into the solution to be tested, adjust the gear switch to an appropriate position, press the reading button, the sum of the value indexed by the gear switch and the index pointer of the indicator is the battery electromotive force +mV value, if To measure one mv, first press the one mV button, use a 2.0~0 scale, and the rest are the same as above.
