THE STICK ANTIMONY ELECTRODE FOR THE MEASUREMENT OF HYDROGEN ION CONCENTRATION
Authors: Uemura Taku , Sueda Hideo 
Published: July 2006

As we have performed various kinds of experiments with the stick antimony electrode, changing their conditions of electrodes and external influences, we may summarise the results of our observations.

(1) The stick antimony electrode in an unstirred solution in contact with air at equilibrium gives a reliable measurement of pH values from pH 1 to 9 inclusive. Recognizing some decrease of accuracy in the results, we may of course apply this electrode for the determination of pH values above pH 9, up to 12.

(2) The value of E.M.F. (m.v.) with the electrode prepared by a Japanese sample and measured against the saturated calomel electrode is obtained by the equation E=53.8 pH—0.7.

(3) We did not take the temperature as a calculating factor, but we always record it during our observation, and we know that E.M.F. value becomes invariably greater when the temperature rises. All our experiments have been made with a temperature varying between 10°C. and 25°C., and the mean error due to the temperature gradient, in this case, is, on an average, about 4%, which is comparable to other experimental errors easily inserted in the estimation of the hydrogen ion concentration.

(4) The surface of a polished antimony electrode is probably covered in a solution with an oxide whose colour is dependent on the pH value of the solution, and the change is more striking when the solution is more acidic. When the pH value of the solution is 1 to 8, the surface of the electrode immersed in the solution becomes black, but if the solution is alkaline (pH is 9 to 12), the immersed part shows a whitish shade of colouring.

(5) When pH is small, i.e. acidic, we generally obtain a higher value of E.M.F. at the beginning of the experiment, and the value decreases and tends to a point of equilibrium; but the opposite takes place in the case of an alkaline solution whose pH is great. We may think that colour change on the surface of the electrode immersed in a solution has perhaps some relation to this transformation of the direction of E.M.F.

(6) The time to reach equilibrium is also dependent on the pH value of the solution. It is comparatively short when the solution is slightly alkaline and its pH value is about 8 to 9, and the colour on the surface of the electrode due to the immersion cannot easily be found in this range of pH. But when the solution is strongly acidic (small pH) or strongly alkaline (large pH), the surface of the electrode changes readily in colour, and the time to reach equilibrium becomes longer.

(7) As for the effect of stirring a solution, E.M.F. deviates to a higher side after it has once reached equilibrium. If we stir the solution from the beginning of the experiment (continuous stirring), E.M.F. thus obtained gives generally a higher value than it is unstirred but when we stop the vibration, E.M.F. value decreases.

(8) Mechanical treatment by the preparation of the stick antimony electrode (Ex. emery paper for polishing) is rather little influenced for obtaining the E.M.F. value, but the original minute impurities contained in an electrode, and the porousness of the electrode cannot be neglected in the determination of E.M.F.

(9) When we have once observed with a solution saturated with antimony oxide, results are obtained at equilibrium, and they are nearly similar to those of an ordinary case. We may, therefore, conclude that the chemical change of the electrode, often discussed by some authors, is not a great factor in the use of the antimony electrode.

(10) When we immersed two electrodes in the same solution but, at different times, the course followed to reach equilibrium are nearly parallel. If the equilibrium is once established by an electrode in a given solution, and we only change the electrode with a polished one, or use the same after polished it again, nearly the same course taken in the first case may also be followed to obtain an equilibrium value.