Educators maintain that "active learning" represents the most effective teaching style. Active learning specifically refers to meaningful, engaging, hands-on experiences with the subject matter, as opposed to the more "passive" methods of traditional lecture. The chemistry laboratory, by nature, should represent the quintessential active learning experience, but educational researchers find this is not the case, largely due to the "cookbook" nature of most laboratory procedures. Slight modifications to traditional, proven experiments can, however, make the laboratory experience significantly more engaging for the student.
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Many high-school chemistry courses introduce acid-base chemistry early in the curriculum. Typically, students perform a titration of an acidic solution (e.g., dilute hydrochloric acid) with a strong base (e.g., dilute sodium hydroxide). Such experiments demonstrate the fundamentals of acid-base chemistry, but the experiments do not convey the practical applications of the approach. Numerous experiments have been published that involve the titration of acidic or basic household chemicals and foods, including vinegar (acetic acid), antacid tablets (calcium carbonate), lemon juice (citric acid), vitamin C (ascorbic acid), baking soda (sodium bicarbonate), aspirin (acetylsalicylic acid) and borax (sodium tetraborate) A particularly engaging twist is to allow the students to verify the manufacturer's claims stated on the product's container, such as the claim of 5 per cent acetic acid in white vinegar.
Although complexometric titrations for water hardness are more advanced than acid-base titrations, they are still within the purview of a high-school chemistry class. The method involves using ethylenediaminetetraacetic acid (EDTA) to complex (i.e., bind to) the magnesium and calcium ions responsible for "hard" water. Students should be encouraged to collect their own samples, such as tap water from their homes or water from nearby rivers, lakes and streams. If one or more students' homes are equipped with water softeners or filtration systems, this also provides an opportunity to test the effectiveness of such devices.
Most high-school chemistry labs are not equipped with the necessary equipment to test for environmental pollutants such as pesticides, but instruments such as pH meters are commonplace. This provides students the opportunity to collect their own samples from rivers, lakes and streams. A more interesting variation of this project would include soil samples, which require special collection and handling procedures. If global positioning system (GPS) devices are available, students could record the exact coordinates of each sample to determine if any correlation exists between geographic position and soil pH. The experiment could also be repeated at various times throughout the school year to see, for example, if the pH of natural bodies of water exhibit seasonal changes.
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