T H E Heat O F Neutralization O F Strong Acids and Bases in H I G H L Y Dilute Aqueous Solutions
T H E HEAT O F NEUTRALIZATION O F STRONG ACIDS AND BASES IN H I G H L Y DILUTE AQUEOUS SOLUTIONS]
Can. J. Chem. Downloaded from www.nrcresearchpress.com by 86.145.230.179 on 01/15/13 For personal use only.
ABSTRACT 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 5x10-" N to 3x10-* N,which is sufficiently low to permit an accurate extrapolation to be made down to zero concentration. The extrapolated values obtained were: for 11:SO4-NaOH, 13.48 3~0.05 lccal. per gm-equiv. and for HCI-NaOH, 13.523Z0.05 kcal. per gm-equiv. These values, which correspo~ld the process H30++ OIi- + 2H20, are signifito cantly higher than the values of 13.32-13.37 kcal. obtained on the basis of previous calorimetric studies i n a llluch higher concentration range. The present values, however, agree well with those calculated by Harned and co-worlrers and by Everett and Wynne-Jones from electrochemical data. INTRODUCTION
Although heats of neutralization of strong acids by strong bases have been measured on very many occasions, there has remained a distinct discrepancy between the results obtained by direct calorimetry and those calculated from electrochemical data. The classical calorimetric studies of this problem are those of Richards and Rowe (12) and of Richards and Hall ( l l ) , who worlted with a variety of strong acids and bases, a t concentratiolls (after mixing) of 1 A4 and higher. Vario~isworliers, including Rossini (13), Pitzer (lo), and Kegeles (8), have employed heat ol dilution and other thermochemical data to calculate from Richards ' results the heat of neutralization a t infinite dilution and a t 25" C., and have obtained valuqs ranging from 13.32 to 13.37 lical. per gm-ecluiv." Pitzer (10) also made a calorimetric determination of his own from which he obtained a value of 13.36&0.016 Itcal. per mole a t infiilite
Can. J. Chem. Downloaded from www.nrcresearchpress.com by 86.145.230.179 on 01/15/13 For personal use only.
ABSTRACT 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 5x10-" N to 3x10-* N,which is sufficiently low to permit an accurate extrapolation to be made down to zero concentration. The extrapolated values obtained were: for 11:SO4-NaOH, 13.48 3~0.05 lccal. per gm-equiv. and for HCI-NaOH, 13.523Z0.05 kcal. per gm-equiv. These values, which correspo~ld the process H30++ OIi- + 2H20, are signifito cantly higher than the values of 13.32-13.37 kcal. obtained on the basis of previous calorimetric studies i n a llluch higher concentration range. The present values, however, agree well with those calculated by Harned and co-worlrers and by Everett and Wynne-Jones from electrochemical data. INTRODUCTION
Although heats of neutralization of strong acids by strong bases have been measured on very many occasions, there has remained a distinct discrepancy between the results obtained by direct calorimetry and those calculated from electrochemical data. The classical calorimetric studies of this problem are those of Richards and Rowe (12) and of Richards and Hall ( l l ) , who worlted with a variety of strong acids and bases, a t concentratiolls (after mixing) of 1 A4 and higher. Vario~isworliers, including Rossini (13), Pitzer (lo), and Kegeles (8), have employed heat ol dilution and other thermochemical data to calculate from Richards ' results the heat of neutralization a t infinite dilution and a t 25" C., and have obtained valuqs ranging from 13.32 to 13.37 lical. per gm-ecluiv." Pitzer (10) also made a calorimetric determination of his own from which he obtained a value of 13.36&0.016 Itcal. per mole a t infiilite
References: 1. BENDER, and BIERMAN, J. J . Am. Chem. Soc. 74: 322. 1952. P. W. W. N. J. Am. Chem. Soc. 76: 4289. 1951. 2. BIERMAN, J. a n d WEBER, 3. C.~LVET, MCm. services chim. Ctat (Paris), 32: 168. 1946. E. 1682 CANADIAN JOURNAL O F CHEMISTRY. VOL. 34, 1956 Can. J. Chem. Downloaded from www.nrcresearchpress.com by 86.145.230.179 on 01/15/13 For personal use only. 4. CALVET, E. Report to the Commission on Thermochemistry. International Union of Pure and Applied Chemistry. 1952. D. W. 5. EVERETT, H. and WYNNE-JONES, F . K. Trans. Faraday Soc. 35: 1380. 1939. 6. HARNED. S. and OWEN. 13. Chem. Revs. 25: 31. 1939. H. 13. 7. HARNED; H. S. and ROBINSON, R. A. Trans. Faraday Soc. 36: 973. 1940. 8. I