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A PORTABLE MIXTURE CALORIMETER OF HIGH ABSOLUTE ACCURACY DWIGHT F. MOWERY, JR. Ripn College, Ripn, Wisconsin
MANYtypes of portable calorimeters designed to measure heats of mixing or neutralization and suitable for student use have been described in the literature (1-8). Although the 'precision of the best of these (4,8)is about 0.2%, the absolute accuracy in neutralization measurements is either not specified (8) or is claimed to be about 1%-274 (4)). In most cases a greater volume of one solution than the other must be used. This complicates comparison of student results with the literature, which usually records heats of neutralization for equimolar quantities of solutions of t,he same concentration. The present equipment was designed to provide a more rapid and uniform mixing of the solutions and a t the same time allow the use of equal volumes. It requires only one Beckman thermometer upon which both the initial and final temperatures are read. The apparatus, drawn to scale in the figure, consists of a Dewar flask ( a ) of inside dimensions z3/4 X 7 S / rin. which is centered, by means of spring clips, in a metal jacket (b) whose inside wall is maintained a t 25 O.l°C. by circulating water from a thermostat through a copper coil soldered to it. Inside the Dewar flask is a lightweight metal bucket supported by glass rods ( d ) which move up and down with the rotating Lucite disc (g) whose center is cut out to clear the fixed center tube holding the thermometer. The bucket, held up by springs between discs (fl and (g), has a l-in. hole in the bottom which is sealed by a conical plug and silastic gasket (c) attached to glass rod ( e ) . Disc (f), with a groove for the driving belt, is made of '/,-in. Lucite and fits tightly around the outside member of an automobile front-wheel bearing. The two rods (d) move
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caI0rimot.r
for Meaeurement of H..t
of Miring or Noutrau..tion
JOURNAL OF CHEMICAL EDUCATION
up and down freely through holes in this disc while the two upper ends of rod (e) are fastened securely to it by set screws. The inner member of the wheel bearing is pressure-fitted t o the lower end of a short a/l-in. brass tube whose upper end is soldered securely into a heavy brass plate, fitted with two half-inch rods which are clamped t o uprights fastened to opposite sides of the metal jacket. A 3/16-in.Lucite plate fastened to the underside of the heavy brass plate covers the top of the calorimeter but allows enough visibility t o work the driving belt into position through two holes (not shown) in the jacket. Driving power is provided by a smoothstarting constant-speed motor clamped to the upright rods. In operation, one of the solutions to be mixed is placed in the Dewar flask and the other in the bucket. The calorimeter cover, rotating mechanism, and bucket are carefully lowered as a unit and clamped in position, rods (d) and (e) having previously been adjusted up or down so that the liquid in the Dewar flask is about in. below the top of the bucket. The belt is worked into the groove in disc (f)and the motor started slowly and gradually increased to 80 r.p.m. After 15 min. the solutions are rapidly and thoroughly mixed by depressing glass plunger (h). This pushes down disc (g) and submerges the bucket at the same time opening the hole in its bottom. A metal spiral on the thermometer causes a downflow inside and an upflow outside the bucket. Two spring latches (i) hold disc (g) and the bucket down and springs on (h) return it, when released, t,o its original position out of contact with (g). The maximum temperature is usually reached about 1 min. aft,er mixing thereby making all temperature readings easy t.o obt,ain with accuracy.
which the heat of neutralization could be calculated as 13.40 0.03 kcal. Nine trials using citric acid yielded an average temperature increase of 2.949 e 0.003"C. at an average starting temperature of 24.99'C. which gave a heat of neutralization of 12.65 0.02 kcal. All errors specified are probable errors on the 0.01 level of significance using the Student &test (12). Heat capacities of the salt solutions produced were 0.982 for NaCI, 0.985 for NaOAc, and 0.961 for NaHICit., all being expressed as cal./g.
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Temo Solutions mized with 0.5 M NaOH 0.51 M HCI
13.65 ( 9 )
Stmdardiza,
LITERATURE CITED ( 1 ) GRUBB,A. C., Znd. Eng. Chem., 18, 163 (1926). H . S., J. CHEM.EDUC.,12,285-6 (1935). ( 2 ) VANKLOOSTER, ( 3 ) V O ~ DR., D., J. Am. Chem. Soe., 59, 1516 (1937). ( 4 ) LIVIN~STON, R., AND W. HGRWITZ, J. &EM. EDUC., 16, 287-90 (1939). I . , AND R. H. WRIGHT, J. CHEW. EDUC.,18, 5 1 s ( 5 ) CAMERON, 12 (1941). J. ( 6 ) PAITISON,D. B., J. G. MILLER,AND W. W. LUCASSE, CHEM.EDUC.,20, 319 (1943). H., AND E. RICHTER, Monatsh., 80, 51&16 ( 7 ) TSCHAMLER, (1949). W. H., J. CHEM.EDUC.,33, 51S20 (1956). ( 8 ) SLABAUOH, F . T., JR.,AND W. B. MELDRUM, "Physi~&l Chem( 9 ) GTJCKER, istry," 1st. ed., Amerioan Book Co., New York, 1942, p. 323. T . W., AND B. J. MAIR,J. Am. Chem. Soc., 51, (10) RICHARDS, 739 (1929). (11) RICHARD^, T. W., AND B. J. MAIR,J. Am. Chem. Soe., 51, 740-7 (1929). (12) , . ROSSINI.F. D.. Editor. "Exoerimental Therrnoohemistry," interscience ~ublishers,'~ew ~ o r k 1956, , p. 305. T. W., AND L. P. HALL,J. Am. Chem. Soc., 51, ( 1 3 ) RICI~ARDS, 731-6 (1929). T. W., B. J. MAIR,AXD L. P. HALL,J. Am. ( 1 4 ) RICHARDS, Chem. Soe., 51, 729 (1929). T. W., AND F. T. GUCKER, JR., J . Am. Chem. ( 1 5 ) RICHARDS, Soc., 51,723 (1929). L.J., R. H. LAMBERT, AND J. A. GIBSON, JR., (16) GILLESPIE, J . Am. Chem. Soc., 52, 3810 (1930).
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MAY, 1957
1.0062 -0.0506
The author wishes to commend Byung Cho Kim and Rodell Singert for their conscientious effortsin performing much of the routine experimental work of this paper.
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34, NO. 5,
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ACKNOWLEDGMENT
In order to test the calorimeter, 203.8 g. (200 ml.) of 0.5000 M carbonate-free sodium hydroxide (sp. gr. 1.019) solution from a thermostat a t 25% was weighed into the Dewar flask and exactly 200.0 ml. of 0.51 M hydrochloric, acetic, or citric acid (c.P. reagents at 25'C.) was delivered from a volumetric flask, each delivery being checked by difference in wt. to the nearest 0.1 g. The Bureau of Standards certified Beckman thermometer used for temperature measurement,~wes read every 3 min. for 15 min. before mixing and every min. for 6 min. and then every 3 min. for 9 min. more after mixing, giving a total time for each run of 30 min. The clean dry calorimeter was allowed to come to thermal equilibrium in the 25" jacket for a t least 8 hr. before each run. The heats of neutralization were calculated in the usual way from large-scale timetemperature plots (4). Eighteen trials with HC1 yielded an average temperature increase of 3.165 0.003"C. at an average starting temperature of 24.89"C. Using the literature value of 13.65 kcal. for the heat of this neutralization, the heat capacity of the calorimeter could be calculated as 33.4 + 0.4 cal./deg. Nine trials using acetic acid gave 0.004°C. an average temperature increase of 3.105 at an average starting temperature of 25.00°C. from
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It is clear from the table that the heats of neutralization of acetic and dtric acids as determined with this calorimeter, using hydrochloric acid for standardization, have probable errors of 0.2270 and 0.16%, respectively, which bracket the most accurate values available in the literature. The literature values were corrected to 2 5 T . by means of the tabulated temperature coefficients calculated from available heat capacity data (13-16).
EXPERIMENTAL RESULTS
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coeff,
Heat Heat ofneut. (kcal. at W C . ) of neut. ((kcal./ LitemThis "C.) lure calorimeter
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