A comparison of chemical reference materials for solution calorimeters

Area of Science:

• Thermochemistry
• Analytical Chemistry

Background:

• Solution calorimeters are essential for measuring heat changes during dissolution.
• Different calorimeter types (semi-adiabatic, isothermal) and their specific requirements influence test substance selection.
• Standardizing calibration procedures is crucial for accurate thermochemical measurements.

Purpose of the Study:

• To evaluate the suitability of KCl, sucrose, and Tris as test substances for isothermal heat-conduction solution calorimeters.
• To compare the performance of different test substances in terms of sample size, accuracy, and ease of use.
• To identify an optimal calibration standard for isothermal calorimeters.

Main Methods:

• Investigated the enthalpy of solution for KCl, sucrose, and Tris using an isothermal heat-conduction calorimeter.
• Analyzed the impact of sample size and enthalpy of solution on measurement precision and accuracy.
• Compared experimental results with literature values and considered necessary corrections (e.g., for dilution).

Main Results:

• Potassium chloride (KCl) required small sample sizes (2 mg) due to its high enthalpy of solution, leading to larger standard deviations.
• Sucrose, with a lower enthalpy of solution, allowed for larger sample sizes (20 mg), minimizing experimental errors and yielding precise results (6.14+/-0.08 kJ mol-1).
• KCl data required minor corrections for dilution effects, while sucrose showed excellent agreement with literature values.

Conclusions:

• Sucrose is a more robust and accurate test substance for isothermal heat-conduction calorimeters compared to KCl.
• The use of sucrose offers advantages in sample handling and precision, making it a preferred calibration standard.
• Further development, including a certified reference sample, would support the widespread adoption of sucrose for calorimeter calibration.