Potentiometric Measurement – Determination of the pH of an alkali solution, a buffer solution , a
hair shampoo, a hand wash and distilled water.
To carry out potentiometric measurement to determine whether a solution is controlled by the buffer system or by a strong electrolyte.
To prepare the samples with different concentration by adding distilled water.
The potentiometric measurement is to determine the difference in potential between a working (an indicator) electrode and a counter (reference) electrode by using the potentiometer. The working or indicator electrode represents the cathode which locates at the right half-cell whereas the ...view middle of the document...
The reasons of using the electrodes to measure the pH are they have the wide range, highly precision, unaffected by the sample colour or turbidity, low cost, fast response and real time in-situ measurement.
The majority of pH electrodes available are the combination electrodes which they combine the reference and pH sensing elements into single electrode. Separate pH and reference electrodes can still be used, but this tends to be for the highest precision, research measurements. Physically, combination pH electrodes are much more practical to use.
The most important step towards accurate pH measurements is by making sure the pH electrode is calibrated probably. Calibration adjust the slope and offset of the slope is produced using the Nernst equation and is usually expressed as a percentage of a theoretically perfect slope (i.e. 100%). However, the limitation of using Nernst Equation is the temperature should maintain at 250C because it is temperature dependent. Besides that, the presence of additional potentials in the electrochemical cells which also called the liquid junction potential, it could be minimized by a salt such as KCl.
Normally, pH buffers are used as standards to calibrate pH electrode. There are a large number of buffers available of different pH values (pH 1.68, pH 4.01, pH 6.86, pH 7.00, pH 9.18 and pH 10.01 at 25 0C) and of varying quality, so it is important to know what should be using. Well, in this experiment, we are using the buffer solutions with pH 4.00, pH 7.00 and pH 10.00 only.
A calibrated glass pH electrode is used to measure the pH of commercially available shampoos; both concentrated and diluted (i.e. 1:10 and 1:100). An estimate is made whether the pH is controlled primarily by a buffered solution or a strong electrolyte.
Calibration of the electrodes
The experiment had been performed by the first calibrating the electrodes at pH7 and making approximate pH measurements of the various samples.
The glass electrode had been soaked in0.1M KCl solution at least one day prior to its use; it had been stored in the dilute KCl solution when not in used.
Only three buffers solution were used for calibrations such as pH 4, 7 and 10. This would consist...