Measurement of pH (electrometric mathod)

Electrometric method (introduction, principal,mathod, advantage)

Introduction -the pH of a solution can be determined by means of an electrode,whose depends on the hydrogen ion activity. The hydrogen and glass electrodes are typical pH electrodes, through the later one is commonly used ,glass electrode is a condensed or combined electrode i.e. this incorporates a reference electrode junction next to the glass membrane,so that both electrodes are kept in one unit . The pH sensitive glass bulb is made of lithia  glass, which is suitable over entire range .

Principal  

1) the potential difference exist at the interface between glass and a solution containing hydrogen ion.

2) the magnitude of this difference varies with the concentration of hydrogen ions.

3) class electron is used for the pH measurement .

4) the glass electrode consist of earth in glass bulb of special class blown at the end of glass tube.

5) the bulb is filled with dilute acid I e desi normal hydrochloric acid solution, which furnished a constant hydrogen ion concentration.

6) silver silver chloride electrode Makes the necessary electrical connection with the acid.

Eh= k-0.0592(pHx - pHk)

              pHx = (K - Eh /0.0592)+pHk

Standard reference buffer solution are used to celebrate the pH parameter to set a symmetric potential. Then the pH of unknown solution can be read from the panel of pH meter.

Mathod-

1) initially , the temperature is said to the solution temperature, as it effect the pH of solution. All PH metres have provision for temperature compansation.

2) the electrodes are emerged in a standard buffer solution of PH 7.0 . Assymetric potential control knob is altered until the metre reads the known PH value of the buffer solution.

3) the instrument is further celebrated using standard pH buffer for 10 and pH 9.14.

4) the electrode is rinsed with water.

5) the bulb of the glass membrane electrod immersed  in the test solution.

6) the pH value of the solution is read from the metre directly.

Advantage -

1) glass electron is not affected by oxidation reduction system there is no exchange of electron.

2) sensitivity of electromagnetic method is high. Hell's accurate measurements can be obtained.

3) the electrode stabilized equilibrium very rapidly.

4) the pH range of measurement is large.