Systematic errors in an isoperibol solution calorimeter measured with standard reference reactions

Abstract

Syste mati c erro rs in an isope ribol calorimete r of a wid e ly.used design, amou nting to a bout 0.5 pe rce nt of the e nd othermi c enthalpy of solu tion of S RM 1 655 (KCI) in H20 , were fou nd to be th e res ult of e rro rs in hea t leak co rrections due to in adeq uate s tirring and comm onl y used calo rimetric procedures.Other systematic e rrors we re found in meas urements of the enthalpy of soluti o n of the exothermic reaction of tri s(hydroxymethyl)aminomethan e in aq ueou s HCI so lution.Recom mended procedures are summarized.Key words: Calorime try; enth alpy of so luti on; KCI ; so luti on calo rim etry; standard re ference materials; the rmochemistry; tris(h ydroxymeth yl)amin omethane.

The enthalpy of solution of SRM 1655 (KCl) in H2O

“…7 perce nt in th e enthalp y of solution of KBr measured by three high-precision ca lori meters. Another recent stud y [3] showed errors in heat tra nsfer co rrecti ons in iso peribol cal orimeters due to some cal orim etric procedures. Th ese sources of un certainty ca n be avo ided by th e use of a standard reference material of KCl from a single source (such as SRM 1655) if the recomm ended procedures are followed .…”

“…15 0 J·mor l (0.8%). This was probab ly due to d ifferent methods of sample preparation and drying as well as systemati c errors in the calorimetry [3]. Gunn [4] s howed differences of as much as 35 J.mor l (0 .2%) in M ,o)n of samples with different ori gin s and drying procedures.…”

“…The remainder of A was sieved through U.S. Standard (bronze) Sieves into the following portions 3 : (1) passed #18 sieve and was retained on #35 sieve, (2) was between #35 and #50 sieves, (2) was between #50 and #100 sieves, and (4) passed #100 sieve. A little less than 40 percent (by volume) of the material was in each of portions (1) and (2), about 20 percent in (3), and less than 1 percent in (4)_ Only a few particles were retained on the #18 sieve (> 1000 J.Lm). When sample P was similarly sieved, portion (1) was about 25 percent of the total, portions (2) and (3) were each about 35 percent, and portion (4) about 10 percent.…”

“…The reaction vessel in this adiabatic calorimeter is surrounded by a vacuum (P <O.lPa), the platinum-lined silver vessel has an essentially isothermal poli s hed surface, and the ad iabatic shield is automatically co ntrolled to follow the temperature of the reaction vessel; thus, there is negligible heat transfer between the vessel and the surroundings and the system is not subj ect to the errors in heat leak co rrections which may exist in some other calorim eters [3,9].…”

“…The "hot or cold" spots due to inadequate stirring, a problem III some calorimeters [3], are relatively unimportant where there is negligible heat transfer between the vessel and the environment. In this calorim eter, the propeller-type stirrer is located immediately below the sample container; this arrangement provides effective stirring.…”