pH-composition relations in the system Na2OSiO2H2O at 20° C☆

Abstract New apparatus and technique for the accurate determination of electromotive force and pH data of solutions are described. These have been used in an extensive investigation at 20° C. of the pH-composition relationships of sodium hydroxide and sodium silicate solutions of the five Na 2 O: SiO 2 molecular ratios 1:0.487, 1:1.009, 1:1.492, 1:1.996 and 1:3.015 (orthosilicate to trisilicate range). The results are of interest as a contribution toward understanding the constitution of silicate solutions, and wherever pH may be used for control purposes in the practical application of silicates. At the trisilicate ratio where pH changes with time, pH is a function of the history of the silicate solution. Comparative colorimetric values by the Taylor indicators are given. Use of these indicators is hardly practicable at concentrations below 0.01 per cent Na 2 O. The density or specific gravity of sodium hydroxide and sodium silicate solutions varies with concentration ( A = % Na 2 O) according to the relation d = 1 + aA + bA 2 + cA 3 over a considerable range.