Before using a pH meter to calibrate it, each pH electrode is used for measurements, something different and its characteristic changes with age. Without the proper pH meter calibration results are usually at least a few tenths of the unit. pH meter calibration performed with buffers of exactly known pH (which were marketed as solutions), immersed in the pH electrode and pH meter data are corrected. I performed calibration, almost on its own (ask only change for buffer if necessary).
To calibrate, I turned the meter on using the button on top and placed electrode in the solution for which I was to determine the pH, following with Rinsing the meter with distilled water and gently blot the end dry with a paper towel. Submerge the meter up to the cap line in the 7.0 calibration solution and adjust the screw labelled pH 7 on the top of the meter with a screwdriver until the meter reads 7.0. And rinsed the meter with distilled water and gently blot the end dry with a paper towel. Next, submerge the meter up to the cap line in the 4.0 calibration solution and adjust the screw labelled pH 4 on the top of the meter with a screwdriver until the meter reads 4.0. After calibrating the pH meter, I turned the meter off, replaced the cap, and discarded their calibration solution.
I calibrated 0.25M and 1M of HCl to observe the accurate results from my practical experiment and the result I achieved are stated below in the table.
The result I attained were different from the result which were given is because the accuracy and precision of the various electrodes have assessed between the result of my practical experiment and the results which were given, pH-range of recordings of solutions with known pH values. Some electrodes are quite correct. For some electrodes accuracy depends on the true pH values, while such dependence has been tested and determined in relation to the accuracy of the electrodes. Both accuracy and precision will be affected if pH recordings made on solutions included with pH values outside the pH range of the calibration buffer. My results show that the accuracy and precision of these electrodes are not as fixed and known parameters. Electrodes should be checked before use, and electrodes with low accuracy and precision are to be excluded from further use.
If I not followed the addressed points below, I would have discovered an error.
- Rinsing the electrodes with distilled water before placing in another solution.
- Making sure the pH meter is up to date, e.g. Battery.
- Stirring the solution in a circular motion with the pH meter.
- Readings of pH or adjustment of the pH with the appropriate acid or base.
- Allowing enough time for meter’s reading to stabilise.
- The hydrogen ion concentration of a solution of pH 2.5
= 10-2.5
= 3.16×10-3 M
- The pH of 0.25M acid solution
= -log (0.25)
= 0.602pH
-
The concentration of H+ ions in a solution of pH 1.0
pH = -log10 [H+]
-1 = +log10 [H+]
[H+] = 1×10-1
= 0.1M