Demonstrations as a Tool for Ironing-Out Preconceptions

Even experienced chemists/instructors sometimes fail in the correct prediction of certain phenomena. An illustration of the previous assertion is given through the chemical reaction between sodium sulfate and concentrated sulfuric acid. The potential importance of the proposed experiment is strengthened by the results of a poll performed on 47 students from the first, second, and final year of study. The experiment is further extended to the whole series of alkali metal sulfates (ammonium sulfate was also included). The increase of temperature was monitored in a very simple reaction system, via a thermocouple thermometer. An attempt is made to explain the observed trend of ΔT values in terms of neutralization of a Brønsted acid and a Brønsted base and a more sophisticated explanation is offered in terms of the lattice energy. The “anomalous” value for the reaction with ammonium sulfate is tentatively explained in terms of the much stronger hydrogen bonds formed in ammonium hydrogen sulfate compared to those found in the alkali metal hydrogen sulfates.