THE HEAT OF NEUTRALIZATION OF STRONG ACIDS AND BASES IN HIGHLY DILUTE AQUEOUS SOLUTIONS

Heats of neutralization of sulphuric and hydrochloric acids by sodium hydroxide have been determined, using a microcalorimeter of the Tian–Calvet type. The range of concentrations employed was 5 × 10−4 N to 3 × 10−2 N, which is sufficiently low to permit an accurate extrapolation to be made down to zero concentration. The extrapolated values obtained were: for H2SO4–NaOH, 13.48 ± 0.05 kcal. per gm-equiv. and for HCl–NaOH, 13.52 ± 0.05 kcal. per gm-equiv. These values, which correspond to the process H3O+ + OH− → 2H2O, are significantly higher than the values of 13.32–13.37 kcal. obtained on the basis of previous calorimetric studies in a much higher concentration range. The present values, however, agree well with those calculated by Harned and co-workers and by Everett and Wynne-Jones from electrochemical data.