Measurement of pH using pH meter

Aim

To measure the pH of a given sample

Apparatus Required:

1. pH meter
2. pH Electrode
3. Duffer solution
4. Thermometer

Theory:

Introduction:pH is a measure of the acidity of an aqueous solution. It is related to the concentration of hydrogen ion, H+. The pH scale can tell if a liquid is more acid or more base, just as the Fahrenheit or Celsius scale is used to measure temperature. The range of the pH scale is from 0 to 14 from very acidic to very basic. A pH of 7 is neutral. A pH less than 7 is acidic and greater than 7 is basic. Each whole pH value below 7 is ten times more acidic than the next higher value. The dissociation of water into hydrogen and hydroxide ions is the basis for the pH scale. The pH is related to the concentration of hydrogen ions by the formula, pH = -log[H+]. It is a logarithmic relationship. When the concentration of hydrogen ion changes by a factor of 10, the pH changes by a factor of 1. Many chemical processes are pH dependent and careful control of pH is important consideration. Solution pH is an important property that is measured by means of a pH meter.

A pH meter and its electrodes form a sensitive electrochemical device that will allow an accurate, reproducible, and reliable measurement of the pH of a solution (see Figure 1). A pH meter is essentially a voltmeter that measures the voltage of an electric current flowing through a solution between two electrodes. There is a direct relationship between the voltage and the pH of a solution. As a result, the meter on the instrument is calibrated directly in pH units. Two electrodes are required. One of them is called a glass electrode. This electrode is sensitive to the concentration of H+ ions in the solution. The other electrode is called the reference electrode and its operation is independent of the composition of the solution. The two electrodes are sometimes combined into a single entity called a combination electrode.

Formula:Ph= - log(H+)

Procedure:

1. Prepare buffer solution of PH4 and Ph 9.2 by dissolving the respective buffer tablets
2. Measure the temperature of the buffer solution and adjust the temperature to penetrate.
3. Dip the electrode in the buffer solution.
4. Swich on the pH meter.
5. Push the Ph/Mv switch to ph positive and STBV/READ switch to read position and adjust CAL control to set on the read out and wait for 30 seconds
6. Set STBV/READ switch to STBV position to move the container with pH and buffer solution.
7. Wash the electrode with distilled water and clean with tissue paper.

pH measurement of given sample:

1. Measure the temperature of the given sample and set the temperature control and immersed electrode in the given sample.
2. Set the Ph/Mv switch to Ph position and STBV/READ switch to read position and wait for 30 seconds.
3. The pH value of the sample will be displayed in the read out.

Tabulation:

Result:

The PH value of the given solution was measured.