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Types of pH standard solutions
When measuring pH, the meter must be calibrated using a standard solution. There are
several kinds of standard solutions. For normal measurement, two standard solutions
(with a pH of 7 and 9) are sufficient to accurately calibrate the meter.
pH 1.68 standard solution: Oxalate
pH 4.00 standard solution: Phthalate
pH 6.86 standard solution: Neutral
phosphate
pH 9.18 standard solution: Borate
pH 12.45 standard solution: Saturated
calcium hydroxide solution
9.7
Conductivity Measurement (Optional)
"Conductivity" is an index that expresses the ease with which electric current flows through a
material. Conductors are categorized either as "electron conductors," such as metals and
other substances which use free electrons to conduct electricity, or "ion conductors," such as
electrolytic solution or fused salt, which use ions to conduct electricity. This section deals with
the kind of conductivity that pertains to ions, especially the conductivity of electrolytic solution
that uses water as the solvent. As shown in Fig. 2, two pole plates with an area A (expressed
2
in m
) are positioned parallel to each other, separated by distance l (expressed in m), then
solution is poured into the cell until full and alternating current is run between the plates.
0.05 mol/L tetra-potassium oxalate aqueous solution
0.05 mol/L potassium hydrogen phthalate aqueous solution
0.025 mol/L potassium dihydrogen phosphate, 0.025 mol/L
sodium dihydrogen phosphate aqueous solution
0.01 mol/L tetra-sodium boric acid (boric sand) aqueous solution
Saturated hydrogenated calcium solution
Polar plates a m
Fig. 2 Conductivity cell imitative
Solution
2
x2
9 REFERENCE
169
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