Define Reagents for Measurement of pH?

Buffer solutions of pH 4, pH 7 and pH 9.18 for calibration and an unknown solution (i.e. solution of unknown pH)

You can prepare these buffer solutions (of pH 4, 7 and 9.18) by following the steps enumerated herewith:

1. Buffer solution of pH 4:

It is prepared by dissolving buffer tablet of pH 4 in a 100 ml volumetric flask and diluting it up to the mark with distilled water. Alternatively, it may be prepared by dissolving 1.021 g of potassium hydrogen phthalate in distilled water in a 100 ml volumetric flask and making the solution up to the mark.

2. Buffer solution of pH 7: Dissolve a buffer tablet of pH 7 in distilled water in a 100 ml volumetric flask and make up the solution up to the mark with distilled water. Alternatively, dissolve 0.340 g of potassium dihydrogen phosphate (KH₂ PO₄) and 0.3550 g of disodium hydrogen phosphate (Na₂HPO₄) in distilled water in a 100 ml volumetric flask and make up the solution to the mark.

3. Buffer solution of pH 9.18: Dissolve a buffer tablet of pH 9.18 in distilled water in a 100 ml volumetric flask and make up the solution up to the mark. Alternatively, dissolve 1.906 g of borax in distilled water in a 100 ml volumetric flask and make up the solution up to the mark.