15-05-2013, 04:30 PM
A Seminar on Digital pH Meter - Use & Calibration
Digital pH Meter.ppt (Size: 439.5 KB / Downloads: 51)
What is pH ?
pH stands for “potential of hydrogen”.
A unit of measure which describes the degree of acidity or alkalinity of a solution.
It is measured on a scale of 0 to 14.
The formal definition of pH is the negative logarithm of the hydrogen ion activity.
pH = -log[H+]
What is a pH Meter?
An instrument that measures the H+ ion concentration (pH) of a solution using an ion sensitive electrode which will ideally respond to one specific ion, in this case H+
A typical modern pH meter has a glass and reference electrode in one tube.
History
Mr. Sorensen devised the pH term and pH scale.
Apparatus for Testing Acidity pH Meter.
Arnold O.Beckman invented a pH meter for measuring acidity and alkalinity.
How does pH meter work?
The pH meter has two electrodes in one tube, glass and reference electrode.
A saturated KCL and HCL solution is contained in a tube which is inside of an outer tube that will have contact with the solution to be measured.
This outer tube has a double glass bulb with Na+ which makes an ion specific electrode. When measuring the pH of a solution, a salt bridge forms.
The Na+ ion, not H+, crosses the glass membrane of the pH electrode and allows for a change in free energy which is measured by the pH meter as the concentration of H+.
PH Value
The pH value of a substance is directly related to the ratio of the hydrogen ion and hydroxyl ion concentrations.
If the H+ concentration is equal to OH- the material is neutral.
pH=7
If the H+ concentration is higher than OH- the material is acidic.
pH is less than 7.
If the OH- concentration is higher than H+ the material is alkaline.
pH is greater than 7
Measuring the pH of a Solution
Always rinse electrodes with de-ionized water prior to placing in a solution for pH measurement.
Allow meter to stabilize for 30 seconds or a minute, then read.
Remove electrodes and rinse with de-ionized solution.
The pH bulb should always be stored wet preferably in pH 4.0 buffer with 1/100 KCl.
Other buffers or tap water can be used for storage.
Application
Medical usage like blood pH
Petrochemical industry
Food and Agriculture
Other chemical process Pharmaceutical
Soil testing