Thermometric Determination of Blank with 2 EQPs

This note describes the determination of the blank value for titration curves having two EQPs. As an example, the titration of a mixture of phosphoric and sulfuric acid with sodium hydroxide (NaOH) is shown.

Background 

In a thermometric titration the enthalpy change is monitored in the course of a titration by measuring the small difference in temperature induced by the chemical reactions.

The titration EQPs are recognized and evaluated using a segmented evaluation procedure (second derivative of the curve).Thermometric titrations with more than one EQP require one blank correction for each individual EQP.

The thermometric titration allows a rapid and accurate analysis that can be fully automated with the Autosampler and a thermometric sensor.

Reaction

1st EQP:

H₂SO₄ + NaOH  ---------->  Na⁺ + HSO₄^- + H₂O

HSO₄^-  + NaOH  ---------->  Na⁺ + SO₄^2- + H₂O

H₃PO₄ + NaOH  ---------->  Na⁺  + H₂PO₄^1- + H₂O

2nd EQP:

H₂PO₄^- + NaOH ---------->  Na⁺ + HPO₄^2- + H₂O

(For the method to measure a mixture of two acids by thermometric titration, download the method M771)