I n arsenic trichloride AsCla+ and C1are the ions characteristic of the solvent and correspond to H30+ and OH- in aqueous solutions. Thus the neutralization of the Lewis acids, stannic chloride and titanium tetrachloride, in arsenic trichloride by a monoacid base pyridine can be represented as :
+
[AsC12]2+[SnC16]2- 2
2 C1-
[
0
+AsC12
+
e O A s C l 2 ] SnCle + 2 hsC13 2
G [0 +
[AsCI~]2+[TiCl~]2-2
2 C1-
e
AsC12
AsC12] Tic16
+
+ 2 AsC13
2
From this account i t appears that in these titrations a fundamental difference exists in the two types of solvents, which has been recognized since early times. LITERATURE CITED
(1) Anderson, H. L., Lindqvist, I., Acta Chem. Scand. 9, 79 (1955). (2) Davis, M. M., Schuhmann, P. J., Lovelace, M. E., J . Research Natl. Bur. Standards 41, 27'( 1948). (3) Garber, E. B., Pease, L. E. D., Luder, W. F., ANAL.CHEM. 25, 581 (1953). (4) Goyal, K., Paul, R. C., Sandhu, S. S., J . Chem. SOC.1959, 322. (5) Gutmann, V., Monatsh. 83, 159 (1952). ( 6 j Zbid., 84, 1191 (1953). (7) Zbid., 85, 393 (1954). ( 8 ) Zbid., p. 404. (9) Zbid., p. 1077. . (10) Gutman, V., 2. anorg. u. allgem. Chem. 266, 331 (1951). (11) Zbid., 270, 179 (1952).
(12) Henry, M. C., Hazel, J. F., McNabb, W. M.,Anal. Chim. Acta 15, 187 (1956). (13) Luder, W. F., McGuire, W. S., Zuffanti,. S.,. J . Chem. Educ. 20, 344 (1943). (14) blanhas, B. S., Paul, R. C., Sandhu, S. S., J . Chem. SOC.1959, 325. (15) Paul, R. C., Chander, K., Singh, G., J . Indian Chem. SOC.35,869 (1958). (16) Paul, R. C., Sandhu, S. S., Singh, J., Eingh, G., Zbid., 35, 877 (1958). (17) Paul, R. C., Singh, J., Sandhu, S. S., Chem. & Znd. (London) 1958, 622. (18) Rice, R. V., Zuffanti, Saveno, Luder, W. F., ANAL. CHEY. 24, 1022 (1952). (19) Seaman, William, Allen, Eugene, Zbid., 23,592 (1951). (20) Singh, J., Paul, R. C., Sandhu, S. S., J . Chem. SOC.1959,845. (21) Spander, H., Brunneck, E., 2. anorg. u. allgem. Chem. 270, 201 (1952). (22) Tomirek, O., Sbornik Celosthtni Pracovni Konf. Anal. Chemikai 1 , 246 (1952).
RECEIVED for review September 5, 1958. Accepted May 4, 1959.
Thermometric Titration of Acids in the Presence of Hydrolyzable Cations F. J. MILLER
and P. F. THOMASON
Analytical Chemistry Division, Oak Ridge National laborafory, Oak Ridge, lenn.
,A
thermometric titration method is presented for determining acid in aqueous solutions of zirconyl ion in hydrofluoric acid, uranyl ion in sulfuric acid, uranyl and copper(l1) ions in sulfuric acid, thorium(1V) ion in nitric acid, and uranyl ion in nitric acid. This "free acid" is determined by titrating the test solution with a standard solution of a base and recording the change in temperature during the titration. Temperature, as detected by a thermistor, is plotted automatically by a recording potentiometer vs. volume of titrant added. The end point of the titration is obtained by extrapolating the straight-line portions of the curve to their point of intersection. Milliequivalent quantities of free acid can be determined. For 0.1 meq., the relative standard error is f1 to &2% a t the 95% confidence level; for 0.01 rneq., it increases to about
&5%.
S
methods are being used for the determination of "free acid"i.e., acid in the presence of hydrolyzable cations. Most of these are discussed by Booman et al. (1). I n general, these methods involve the addition of a complexing agent followed by one of several different types of titrations. EVERAL
1498
ANALYTICAL CHEMISTRY
Thermometric methods of titrations have been known to analytical chemists. Jordan and Alleman ( 3 ) have applied this method most recently. They have shown that by prior consideration of thermodynamic data, the feasibility of a thermometric titration can often be determined without experimentation. EXPERIMENTAL DETAILS
Apparatus. STIRRING MOTOR, A. S. LaPine a n d Co., Catalog No. 38286. The slow-speed shaft that operates at 320 r.p.m. was used. The stirring motor should have a cooling coil of I/*inch diameter copper tubing wound around it. A small flow of water is passed through the copper tubing t o prevent excessive temperature rise in the motor during operation. GLASSSTIRRER. A flat piece of glass, inch wide, twisted into a spiral 11/* t o 2 inches long, was attached t o a glass rod inch in diameter for use as a stirrer. THERMISTOR. A thermistor that is suitable for measuring temperature changes is Type 32-a-1, manufactured by the Victory Engineering Corp., Springfield Road, Union, N. J. It has the following characteristics: Sensitivity in the region of 25' C., 0.04 ohm/ohm/" C. Resistance at 25' C., -2,000 ohms Thermal time lag,
