thermometric titration-introduction,instrumentation,application....

2. INTRODUCTION
 Thermometric titration is one of a number of
instrumental titration techniques where
endpoints can be located accurately and
precisely without a subjective interpretation on
the part of the analyst as to their location.
 Enthalpy change is arguably the most
fundamental and universal property of chemical
reactions, so the observation of temperature
change is a natural choice in monitoring their
progress.

3.  Titrant is added at a known constant rate to a titrand until the
completion of the reaction is indicated by a change in
temperature. The endpoint is determined by an inflection in the
curve generated by the output of a temperature measuring
device.
 The temperature changes observed during a thermometric
titration are the consequence of the heat evolved or absorbed by
the reaction between the analyte & the reagent. The heat or
enthalpy of a reaction ∆H is given by the familiar thermodynamic
expression.
 ∆H=∆G + T∆S
 Where T is the temperature. ∆G is the free energy change & ∆S is
the entropy change for the reaction. The change in the
temperature ∆T during thermometric titration is given by,
 ∆T= -n∆H/K where n is the no. of moles of reactant and K is the
heat capacity of the system. Thus, the total change in
temperature is directly proportional to the no. of moles of analyte.

4. FOR IDEAL CONDITION
 Heat losses or gains from outside
the system via the vessel walls
and cover.
 Differences in the temperature
between the titrant and the titrand.
 Evaporative losses from the
surface of the rapidly mixed fluid.
 Heats of solution when the titrant
solvent is mixed with the analyte
solvent.
 Heat introduced by the
mechanical action of stirring(minor
influence).
 Heat produced by the thermistor
itself (very minor influence).
Idealized thermometric titration
plots of exothermic (left) and
endothermic (right) reactions

5. FOR EXPERIMENT
 Consider the titration reaction:
aA + bB = pP
 Let A represent the titrant, and B the
titrand. At the beginning of the
titration, the titrand B is strongly in
excess, and the reaction is pushed
towards completion. Under these
conditions, for a constant rate of
titrant addition the temperature
increase is constant and the curve is
essentially linear until the endpoint
is approached. In a similar manner,
when the titrant is in excess past the
endpoint, a linear temperature
response can also be anticipated.
Thus intersection of tangents will
reveal the true endpoint.

6. THERMISTOR
 The most practical sensor
for measuring temperature
change in titrating solutions
has been found to be the
thermistor.
 Thermistors are small solid
state devices which exhibit
relatively large changes in
electrical resistance for
small changes in
temperature.
 It is capable of resolving
temperature changes as
low as 10–5 K.
Glass-encapsulated thermistor of the
Thermoprobe.

7. APPARATUS AND SETUP FOR AUTOMATED
THERMOMETRIC TITRIMETRY
• Precision fluid dispensing devices – burets – for
adding titrants and dosing of other reagents
• Thermistor-based thermometric sensor
• Titration vessel
• Stirring device, capable of highly efficient stirring of
vessel contents without splashing
• Computer with thermometric titration operating system
• Thermometric titration interface module – this
regulates the data flow between the burets, sensors
and the computer.

8. A=dosing
device
B = thermometric sensor
C = stirring device
D = thermometric titration interface
module
E = computer
Basic thermometric titration system featuring 859 Titrotherm interface module and
800 Dosino dispensing devices.

9. OPTIMIZATION OF THERMOMETRIC TITRATION
PARAMETERS
 Mixing
 Most of the instrumental noise evident in thermometric titrations is thus due
to the detection of temperature gradients in the stirred titration solution.
Minimization of instrumental noise can therefore be obtained by using
stirring speeds as high as possible consistent with the avoidance of
splashing.
 Probe orientation
 It has been observed by a number of workers in the field of thermometric
titration that there is an optimum placement of the thermistor probe and the
buret delivery tip in the titration vessel.
 Data density
 The Titrotherm thermometric titration software permits data density to be
preset before the start of the titration. The data density stays constant over
the entire titration. With Titrotherm software, the analyst has the option of
altering the sampling rate of the output from the thermometric sensor in the
range of 5 to 25 times per second.
 The data sampling rate is matched to the anticipated titrant consumption and
to the titrant addition rate of the determination.

10. However, it is inevitable that
some shift will occur. For highest
accuracy and precision this shift
should be taken into
consideration.
The Titrotherm software employs a
powerful data-smoothing algorithm
that exhibits a minimum endpoint shift
as a function of the degree of filtering
applied.
The effect of the filter factor on
the endpoint peak shape and
the endpoint shift.
FIG 6 filter factor =20 Fig 6 filter factor=50
Fig 6 filter factor=80 Fig 6 filter factor=100
Optimizing titration
results with software

11. Determination of optimal filter factor

12. APPLICATION OF THERMOMETRIC TITRATION
 Acid-base titrations
Titration of NaOH with 1 mol/L HCl. Titration of HCO3 – in company with CO3
2– by 1 mol/L NaOH
Determination of fully dissociated acids
and bases

13. Titration of weak acids with 1 mol/L NaOH
Titration of weak
acids
Titration of a mixture of nitric, acetic and phosphoric acid
with 2 mol/L NaOH
Titration of acid mixtures

14. Non-aqueous acid-base titrations
Determination of free H2SO4 in copper leach solution by titration in 2-
propanol with 1 mol/L KOH in 2-propanol

15. REDOX TITRATIONS
Titrations with permanganate

16. COMPLEXOMETRIC (EDTA) TITRATIONS
EDTA titration of calcium and magnesium in sea water
Calcium reacts exothermically with EDTA (heat of chelation approximately –23.4
kJ/mol), magnesium reacts endothermically with a heat of chelation of
approximately +20.1 kJ/mol.

17. PRECIPITATION TITRATIONS
Titration of benzalkonium
chloride with sodium dodecyl
sulfate.
Titration of sodium lauryl sulfate
in shampoo by titration with cetyl
pyridinium chloride. Acetonitrile
added to repress micellerelated
phenomena. Note sudden rise in
temperature immediately prior to
the endpoint.

18. REFERENCES
www.metrohm.com/com/.../Titration/BasicsThermometricTitration
.html
www.creative-chemistry.org.uk/alevel/module2/.../N-ch2-08.pdf
Thermal Analysis, 3rd edition W. W. Wendlandt.
Instrumental methods for chemical analysis by H. Willard