Chapter 7 Reference
7.1 pH measurement
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Using standard solutions
Standard solutions are used to calibrate the scale of the pH meter
employed to measure the unknown pH of a solution. Standard solutions
of pH 4, 7, and 9 are used in combination according to the particular
conditions of the solution that is to be inspected.
When the approximate pH value is desired (1-point calibration)
Use the pH 7 standard solution or a standard solution that approximates
the pH value of the solution that is to be inspected.
When it is known beforehand whether the test solution is acidic or
alkaline (2-point calibration)
Acidic: Use the pH 4 and 7 standard solutions.
Alkaline: Use the pH 7 and 9 standard solutions.
When an unknown solution is to be inspected (3-point calibration)
Use the pH 4, 7, and 9 standard solutions.
Other
When finding the pH of other solutions, perform 2-point or 3-point
calibration using pH 2, 4, 7, 9, or 12 standard solutions randomly, then
measure the test solution.
