UNIT 4 scientific practical techniques
1 .PH Probe
A PH probe also known as a PH meter is an electronic device used for measuring the pH (acidity or alkalinity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances). A typical pH meter consists of a special measuring probe (a glass electrode) connected to an electronic meter that measures and displays a digital pH reading
The glass electrodes must be calibrated using a two point method with the appropriate buffer standard. To perform a two point calibration two buffer solutions are required. These buffers should be based upon the normal measurement range that probe operates in. A probe used for measuring the pH of alkali solutions should use pH buffers 7.0 and 10.0. Likewise, a pH probe in an acidic solution should be calibrated with a 2.0 (or 4.0) and a 7.0 buffer solution.
Why this instrument was selected?
The pH probe was selected for analysis because it provides accurate (post calibration) pH readings that are digitally taken to 2dp’s, and as we were dealing with solutions of an unknown pH, it is important to know precisely what the pH of each was, as they may have been used in other experiments needing a specific Ph. The use of this respective piece of equipment allowed us to ensure our reading of the pH of 3 unknown solutions was accurate to 2 decimal places,
The alternative method would be use of PH litmus papers
Litmus papers
Litmus is a water-soluble mixture of different dyes extracted from lichens, especially Roccella tinctoria. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity.
How they are use:
Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic (i.e. alkaline) conditions,
Evaluating and comparing the accuracy of the procedures
Advantage of using a PH meter over Litmus papers
• The PH meter provides a digital reading to 2 decimal places while as the litmus paper gives a rough estimate whether the solution is acidic or alkaline not giving a specific value of levels of the acidity or alkalinity .
Disadvantages of using a PH meter over litmus papers
• For very precise and accurate results the pH meter must be calibrated before each measurement which means the accuracy of the results may be depend on