The Method of Continuous Variation: A Laboratory Investigation of the Formula of a Precipitate

Abstract

The method of continuous variation is applied to the reaction between barium chloride and diammonium hydrogen phosphate in neutral, acidic, and basic conditions. Depending on the medium, barium dihydrogen phosphate, barium hydrogen phosphate, or barium phosphate is precipitated. The precipitates are washed, dried, and weighed. Construction of a continuous variation plot for each condition leads to the deduction of the molecular formula of the phosphate precipitated. This experiment demonstrates the concept of stoichiometric relationships between ions in the formation of compounds and serves to give students practice in calculations involving limiting reagents.

Molecular insight of DREAM and presenilin 1 C‐terminal fragment interactions

“…Furthermore, the Job plot (Fig. B) shows a maximum at HL9 mole fraction (X HL9 ) of 0.5, what is consistent with a 1 : 1 stoichiometry for molecular association of HL9 with Ca 2+ DREAM . These results further suggest that a dimeric DREAM binds to two HL9 in the presence of Ca 2+ or Ca 2+ Mg 2+ .…”

Fabricating Simple Wax Screen-Printing Paper-Based Analytical Devices To Demonstrate the Concept of Limiting Reagent in Acid–Base Reactions

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“…To reinforce its concepts, experiments are continuously designed so that students can better understand molar ratios from a practical standpoint. For example, in the past decade, the Journal of Chemical Education published papers on the subject whereby the favorite techniques to ascertain stoichiometric relationships included mainly colorimetry/spectrophotometry, − conductivity, , electrochemistry, − gravimetry, − titrimetry, , gas generation, − thermochemistry/thermal analysis, , − and catalysis …”