No 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.

Infrared spectroscopy is traditionally used to identify compounds and aid in structure elucidation. However, solid samples require tedious and sometimes messy preparation of KBr pellets or mineral oil mulls and solutions cannot be used because there are no solvents that do not absorb in the IR. Disposable IR cards have simplified sample preparation for IR spectrometry. Moreover, they allow samples to be preserved for long periods, so that results can be verified at a later time. We report an experiment suitable for the instrumental analysis portion of the analytical chemistry course. It employs an internal standard in order to utilize the disposable cards for quantitative analysis. We use potassium thiocyanate as the internal standard because it has few absorption bands in the IR and they do not interfere with the bands of the unknown, benzophenone. Acetone is used as the solvent because it evaporates readily, making no contribution to the spectrum. This lab is useful as a teaching tool to illustrate the use of internal standards and calibration curves and the principle of Beer's law. It can be adapted for the determination of any analyte, provided the analyte and internal standard have distinctly separate IR bands. It is particularly useful in areas such as forensic chemistry, in which lab results are likely to be contested and samples must be preserved for long periods of time.

The generally accepted method to determine iron content in food is by acid digestion or dry ashing and subsequent flame atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry. We have developed an experiment that chemically extracts the iron from an egg yolk and quantifies it using UV–vis absorption spectrophotometry. Only the yolk of an egg is used because it contains almost all of the iron in an egg and the extraction is more efficient than with the whole egg. The experiment is suitable for the instrumental analysis portion of the analytical chemistry course and serves to demonstrate to the students the chemical and biochemical principles that can be used for the extraction of a mineral from a complex organic matrix.

A first-semester general chemistry laboratory experiment for college is described in which students carry out qualitative analysis to identify seven unknown colorless solutions. The experiment serves to correlate qualitative analysis with classification of reactions and can also be used in second-year or advanced-placement (AP) high school chemistry classes.