Short Communication THE DETERMINATION OF HYDROXIDE AND CARBONATE IN CONCENTRATED SODIUhf CHLORIDE SOLUTIONS

Summav. A computer method for the determination of carbonate and hydroxide in con-centrated (2.89 M) sodium chloride solutions is described. The method is based on multi-parametric curve-fitting end can also be applied to salts of dibasic acids with unknown equilibrium constants. The systematic error is not more than 1%. The titration and cal-culation takes less than 20 min. In the potentiometric titration with hydrochloric acid of hydroxide and carbonate of concentrations less than 0.01 M it is often impossible to deter-mine the equivalence point of hydroxide from the inflexion point or first derivative [ 11. The calculation of the hydroxide concentration from the equivalence-points of carbonate is not very accurate. Straightforward Gran plots are sometimes curved, while more sophisticated linearization techniques require accurate values of the equilibrium constants [2,3]. Another method with at least comparable versatility is multiparametric curve-fitting [4-S]. This paper describes the adaptation of the Wentworth method [9], as used earlier by Bos [S] for the titration of mixtures of a weak and a strong acid with sodium hydroxide, for the determination of hydroxide and carbonate in 2.89 M (3.00 m) sodium chloride solutions. Four parameters from the charge-balance equation are adjusted to obtain a centrations of hydroxide and carbonate, and both of carbonate. Theory The symbols are defined in Table 1. Charge-balance equations. The charge-balance least-squares fit, the con-the equilibrium constants equation valid- for each point of the titration curve of a salt of a dibasic acid and a strong base with hydrochloric acid is given b