Demonstrations for high school chemistry


Conductivity demonstrations of ionization develop the. Arrhenius conceptual definition (explanation) of acids and bases and their behavior. ... develo...
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Joseph F. Castka Martin Van Buren High School

Queens, New York City, 11427

Demonstrations for High School Chemistry

These demonstrations and the sequence in which their presentation is suggested may serve to initiate and maintain student interest in such topics as (1)the development of acid-base theories and (2) bond strength. Sources of these demonstrations or variations of them are the texts by Alyea and Dutton' and the not so easily obtainable one by Fowles.2 Students readily frame an operational definition of acids on demonstrations or experiments dealing with taste, indicator reactions, replacement of hydrogen by active metals, and acid-base neutralization resulting in the formatton of water and a salt. Listing of common acid formulas results in student recoenition of hvdroeen as an - ~ " acid constituent. In similar procedures they frame an operational definition of a hase and recognize that hases contain the OH group. Conductivity demonstrations of ionization develop the Arrhenius conceptual definition (explanation) of acids and bases and their behavior. These may include the conductivity of fused salts as well as that of aqueous solutions of acids, bases, and salts. The representative ionization (dissociation) equations are then written. Most high school chemistry courses include the concepts of the BronstedLowry definitions and some include the Lewis definitions. Some of the demonstrations described below may he used for these purposes. Chemical bonds and the role of energy in their rearrangements are fundamental in the development of the basic concepts of high school chemistry. Some of the demonstrations descrihed below may he used in explaining the role of bond strengths . and energies.