Parr Instrument 6755 - Manual (Page 24)

5
Calculations
P a r r I n s t r u m e n t C o m p a n y 22
C
HAPTER
5
Calculations
Standardization
A sample of tris (hydroxymethyl) aminomethane,
commonly called TRIS, is furnished with the 6755
Calorimeter to provide a reliable standardizing re-
agent. TRIS is furnished as a dry powder which can
be used directly from the bottle as supplied without
further preparation, but undue exposure to air and
moisture should be avoided in order to preserve the
integrity of the standard.
For standardizing the 6755 Solution Calorimeter,
solid TRIS can be dissolved in dilute hydrochloric
acid in a controlled reaction for which the amount of
heat evolved is well established. In the recommend-
ed standardization procedure described below, 0.5
gram of TRIS is dissolved in 100 ml of 0.1 N HCl to
evolve 58.738 calories per gram of TRIS AT 25 °C.
1. Tare the Dewar on a solution or trip balance and
add exactly 100.00 + .05 grams of 0.100 N HCl.
2. Weigh 0.50 +.01 gram of TRIS into the 126C Tef-
lon Dish on an analytical balance to an accuracy
of +.0001 g.
3. Assemble the rotating cell; place it in the calo-
rimeter and start the motor.
4. Let the calorimeter come to equilibrium; then
initiate the reaction by depressing the push rod.
5. Analyze the thermogram to determine the net
corrected temperature rise, ∆T
c
. At the conclu-
sion of the test the instrument will report a net
corrected temperature rise, ∆T
c
.
6. Calculate the known energy input by substitut-
ing in the equation:
QE = m[58.738 + 0.3433(25 - T(0.63R))]
where:
QE = the energy input in calories
m = weight of TRIS in grams
T(0.63) = temperature at point 0.63R on the
thermogram
Note: The term, 0.3433(25 – T(0.63R)), adjusts
the heat of reaction to any temperature above
or below the 25 °C reference temperature.
Calculate the energy equivalent of the calorimeter
and its contents by substituting in the equation:
where:
e is expressed in calories per °C.
Determine the energy equivalent of the empty calo-
rimeter by subtracting the heat capacity of the 100 g
of 0.1N HCl from e, as follows:
e’ = e - (100.00)(0.99894)
where:
e’ = energy equivalent of the empty
calorimeter in calories per °C.
100.00 = mass of 0.100N HCl in grams
0.99894 = specifi c heat of 0.1N HCl at 25 °C
Example:
A standardization reaction involving 0.5017
grams of TRIS, and 100.00 grams of 0.100N HCl
producing a net corrected temperature rise of
∆TC = 0.244 °C with 0.63 rise, T(0.63R), at 24.301
°C.
In this reaction the known energy input is:
QE = 0.5017 [58.738+0.3433 (25 - 24.301)]
= 29.589 calories
The energy equivalent, e, of the calorimeter and
its contents is then computed:
The energy equivalent, e’, of the empty calorim-
eter is then computed: