Most first-year college chemistry courses include the concepts of equilibrium, free energy, enthalpy, and entropy and the relationships between them. All are incorporated in one titrimetric experiment presented here. The chemicals used are sufficiently low in toxicity that waste disposal is simple. The chemical operations are straightforward . In this exercise, saturated solutions of calcium hydroxide at two (or more) temperatures are prepared and titrated with standardized hydrochloric acid solution. Using these titration data, the K sp and ∆G ° for the dissolution of calcium hydroxide are determined. ∆G °, ∆S °, and ∆H ° for the reaction are determined from the temperature dependence.

In the analysis of aldehydes and ketones (both for characterizing the functional group and identifying such compounds by the melting points of their derivatives), 2,4-dinitrophenylhydrazine reagent is often used. Of the several formulations of this reagent, the most popular uses sulfuric acid. The method involves making a paste of 2,4-dinitrophenylhydrazine in concentrated sulfuric acid, dispersion of the paste in ethanol, addition of water, and the filtration of the reagent (1). This improvement uses milder conditions, which may obviate the need for the final filtration. Those responsible for preparation of stock reagent solutions for classes should note that this method facilitates scaling up the preparation.To a clean, dry 125-mL Erlenmeyer flask and magnetic stir bar, add 3 grams of 2,4-dintrophenylhydrazine, 20 mL of water and 70 mL of 95% ethanol. Place the flask in an ice bath in a beaker. Stir and allow the mixture to cool. When the temperature reaches 10 °C, with continued rapid stirring, begin the slow addition of 15 mL concentrated sulfuric acid, trying to avoid boiling. If the temperature goes above 20 °C, stop addition until the temperature goes back to 10 °C. When the sulfuric acid has been added, turn off the stirrer, remove the ice-bath and place the flask on a stirrer-hotplate. Stir and warm the flask until the 2,4-dintrophenylhydrazine stops dissolving or the temperature reaches 60 °C, whichever comes first, then continue stirring without heating. When the solution has cooled, filter through a fritted funnel, if necessary. 2,] is a flammable solid, which must be kept moist and is harmful if swallowed, inhaled, or absorbed through the skin. Concentrated sulfuric acid [7664-93-9] is poisonous and corrosive. Its mist can cause severe burns to all body tissue. It may be fatal if swallowed or by skin contact. It is harmful if inhaled and may cause cancer. Ethanol [64-17-5] is flammable and should be kept from ignition sources. Eye and face protection, protective clothing, and gloves must be worn. Hazards

The popular elephant's toothpaste demonstration can be used to demonstrate the effect of temperature on reaction rate qualitatively. Our version is designed for simplicity of execution and to require little class time. Two runs of the reaction are performed at easily achieved temperatures (ice and ambient), the latter being approximately three times as fast. The reaction behind the demonstration, the iodide-catalyzed decomposition of hydrogen peroxide (along with some complicating side-reactions), are discussed in some detail.

Replacing the styrofoam, coffee cup calorimeter with the Snak Jar.

Our previous work correlated bond angles of group V and group VI hydrides (AH3E and AH2E2, respectively, where E represents a lone electron pair) to the electronegativities of the atoms using the fraction of s character to relate the two. Here we have extended the correlation to the AH2X2 series, where A is a group IV atom, carbon, silicon, or germanium and X is hydrogen, fluorine, chlorine, bromine, or iodine, treating each “X” as an individual series. These group IV series are correlated to each other by the atomic radius and electronegativity of the “X” (halide or hydrogen) atom, yielding a single relationship for all of fourteen compounds. The results support three assertions (and their corollaries) that allow students to predict relative hybridization and, thus, bond angles of these dihalides based on readily available electronegativity values.