A Laboratory Manual of Methodology,” Tech. Rept. R59-6, R. A. Taft Sanitary Engr. Center, Cincinnati, November
LITERATURE CITED
(1) Alexander, G. V., Nusbaum, R. E., MacDonald, N. S., J . Am. Water Works Assoc. 46, 643-54 (1954). (2) Burriel-Marti, F., Ray,irez-Munoz, J., “Flame Photometry, pp. 154, 271-5, Elsevier, Amsterdam, 1957. (3) Chow, T. J., Thompson, T. G., ANAL. CHEM.27, 18-21 (1955). (4) Davis, P. S., Nature 183, 674 (1959). (5) Hallbach, P. F., ed., “Radionuclide Analysis of Enviroamental Samples.
1959.
(6) Hillebrand, W. F., Lundell, G. E. F., lLAppliedInorganic Analysis,” p. 626, Wiley, New York, 1959. (7) Leddicotte. G. W.. Revnolds. S. A..
Marion, ANAL. CHEM.34, 778 (1962). (11) Skougstad, M. W., “Flame Photometric Determination of Strontium in Water.” Water Resources Div., U. S. Geol. ‘ Survey, Washington, D. C., October 1957. (12) Sugawara, K., Kayama, T., Kawasaki, N., Bull. Chem. SOC.Japan 29 683-5 (1956). (13) Wade. M. A.. Seim. H. J.. ANAL. ‘ CHEM. 33, 793-5’(1961): RECEIVEDfor review July 2, 1963. Accepted November 20, 1963.
Thermometric Titrations in Glacial Acetic
Acid
HUBERT J. KEILY and DAVID N. HUME Department of Chemistry and laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge
b The automatic thermometric titration method has been applied to the titration of acids and bases in glacial acetic acid. An apparatus has been developed for difflarential titration to eliminate the effects of heats of dilution and mixing. The thermometric end point is particularly useful for the determination of weak organic bases by titration with perchloric acid. For very weak bases, traces of water constitute a disturbing factor because of the basicity of the! water molecule. Under strictly anhyidrous conditions, even diphenylamine, urea, acetamide, and acetanilide are rmeadily titratable.
I
automatic thermometric titration, Ldnde, Rogers, and Hume (12)pointed out that the method does not require ai1 electrolytically conducting solvent or an electrode which must respond to changes in the solution. It should therefore have considerable advantage over conventional electrometric methods of end-point detection for titrations in solvents of low dielectric constant. The present investigation involved a study of the applicability of the thermometric titration technique to acid-base reactions in glacial acetic acid. N INTRODUCING
EXPERIME YTAL
chronous motor rotates the cam through gears which reduce its speed to 0.04 r.p.m., giving a delivery rate of about 2 ml. per minute. The direction of rotation is reversible. The plungers are held against the bar by spring loading, preventing siphoning and expediting filling when the cam is returned to its dwell position. A dialindicator micrometer is attached in such a way as to indicate the position of the bar and permit duplication of the plunger setting to within =kO.001 inch. The syringes are connected to reagent reservoirs by three-way stopcocks for ease in filling. If only one syringe is to be used in a titration, the other is allowed to deliver its contents back to the storage reservoir. Plexiglas covers were mounted over the stands holding the half-pint Dewar
Figure 1. A.
Apparatus. T o be able to compensate, if desired, for heats of dilution and mixing, provision was made for differential thermometric titration.
Two motor-driven syringe burets were designed to be operated either individually or in unison. This was accomplished by attavhing the plungers of two 50-ml., glass, hypodermic-type syringes to a bar which is driven by a cam with a constant rise of 0.130 inch per 15’ of rotation. A 1-r.p.m. syn-
Thermistor bridge circuit
Basic diagram 6. Detailed diagram E l , €2. 1.5-volt dry cells Rlo. 2 0 3 4 ohms Rli. 1030-ohm 1 0-turn Helipot R1z. 25.0-ohm 1 0-turn Helipot R13. 2 4 8 6 ohms R14. 2 0 3 3 ohms 1 000-ohm 1 0-turn Helipot R16. Rle. 500-ohm 1 0-turn Helipot R17. 15,000-ohms R18. 90,000 ohms RT. Thermistor E, e. Net applied voltage and unbalance patential, respectively R13 may be replaced by a thermistor matching RT for differential titrations
39, Mass.
flasks used as titration vessels. Each cover held a thermistor and a heater in a fixed position, and had holes for the buret tip and the shaft of the stirrer. The glass-enclosed electrical heaters were used to adjust the temperature of the solution in the Dewar t o match that of the (warmer) titrant, if desired. The syringe delivery was calibrated by weighing water delivered a t 0.1-inch intervals. Temperature was measured by means of a thermistor and Wheatstone bridge circuit shown in Figure 1. Sensitivity was adjusted by varying the applied voltage, E , linearly from zero to 1.5 volts by means of the bucking potential taken from the voltage divider a t RI6. The imbalance potential, e, was fed directly to the recorder, a 2.0-mv. Leeds and Northrup Speedomax. The bridge components were so chosen that the output voltage of the unbalanced bridge would be essentially linear with temperature over the range of temperature variations encountered in this work and the linearity was checked by comparison with a Beckmann thermometer. The thermistors were Western Electric Co. 14B with a nominal room temperature resistance of 2000 ohms and a negative temperature coefficient of resistance of 3.970 per c. The ordinary, measuring thermistor is connected to the bridge a t RT. A second thermistor may be introduced, replacing R13 for differential thermometric measurements. The fixed resistors in the bridge were calibrated to &O.l% after being built into the circuit. The applied voltage, E , can be estimated to within a few per cent by the voltmeter, V . For accurate temperature measurements, a potentiometer should be used. Calibration of the temperature-measuring system, although necessary if heats of reaction are to be determined, is not required for ordinary analytical applications. Details of the apparatus and its calibration have been described (9). Materials and Reagents. SOLVENT.
Glacial acetic acid of reagent quality contained 0.1 to 0.3’% water by Karl VOL. 36, NO. 3, MARCH 1964
e
543
Fischer titration and was used directly where such quantities of water were not considered objectionable. Essentially anhydrous (
