pH meter

pH electrode

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Buffer Solutions Amazon

Buffer Solutions

by R.J. Beynon, J.S. Easterby

pH meter

In general you will probably use commercially available calibration buffers, sold either as ready solutions or as tablets to dissolve in deionized water. However, it may be interesting to look at the table of standard solutions that can be used for the electrode calibration. pH given is for 25°C:

Standard calibration buffers
substance(s)concentrationpH
hydrochloric acid
HCl
0.1000M1.094
potassium trihydrogen oxalate
KH3C4O8
0.05000m1.679
potassium hydrogen phthalate
KHC8H4O4
0.05000m4.005
potassium hydrogen tartrate
KHC4H4O6
saturated in 25°C3.557
disodium hydrogen phosphate
Na2HPO4
potassium dihydrogen phosphate
KH2PO4
0.02500m

0.02500m
6.865
disodium hydrogen phosphate
Na2HPO4
potassium dihydrogen phosphate
KH2PO4
0.03043m

0.008695m
7.413
disodium tetraborate
Na2B4O7
0.01000m9.180
sodium hydrogen carbonate
NaHCO3
sodium carbonate
Na2CO3
0.02500m

0.02500m
10.012
calcium hydroxide
Ca(OH)2
saturated in 25°C12.45

m stands for molality, M for molarity.

Please note that high pH buffers are less stable, as they tend to absorb atmospheric CO2 which lowers their pH. During calibration you should open the bottle only to pour the buffer to the beaker. Never left the bottle open.

It is also important to remember that pH of buffer solutions change with temperature. pH of potassium hydrogen phthalate solution rises to 4.16 at 80°C. Many pH meters doesn't take these changes into account automatically, even if they allow automatic temperature compensation during measurements.