Academic journal article Science Scope

Charcoal-Can It Corral Chlorine?

Academic journal article Science Scope

Charcoal-Can It Corral Chlorine?

Article excerpt

How many ways have you used water today? Have you ever wondered who used that water before you--and for what purpose? Because our water is used over and over, a faucet has been described as the other end of someone else's drain. Water is obviously one of our most precious resources, and we have a limited supply available for our use. For this reason, the United Nations has proclaimed 2011 as the International Year of Chemistry and, as part of that designation, has invited teachers worldwide to participate with their students in the Global Water Experiment (IYC 2010). Students have the opportunity to take part in four different water-related investigations to assess water quality and then share data with other students around the world. The project began on World Water Day (March 22 each year) and will run throughout 2011. This month's Everyday Engineering column looks at a related water exploration--designing charcoal filtration systems like those used in filtering water pitchers, some coffee pots, and refrigerators. There are several curriculum tie-ins for this lesson; most notably is natural water filtration using different types of sediment, such as sand or gravel.

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In this 5E learning-cycle activity, students will investigate how charcoal (carbon) filters can be used to remove chlorine from water. They will design a filtering system to reduce the chlorine concentration in a sample of water while also minimizing the amount of charcoal that is required. The International Technology and Engineering Educators Association's middle-level standard for attributes of design states, "Requirements for design are made up of criteria and constraints" (ITEA 2002, p. 95). In this lesson, the design requirement is to reduce the presence of chlorine in a water solution. The constraints include the time required for filtration and the amount of charcoal needed, which is a function of the system's total cost.

History

Early Sanskrit writings from the 15th century BC indicate that people attempted to treat and filter their drinking water. The walls of ancient tombs from this time show drawings of the purification of drinking water (see Figure 1) (Baker 1981). Chlorination of water began in the 1800s and is still widely used to purify water today, as it destroys many harmful organisms. Charcoal filters also have a long history: "The efficacy of powdered charcoal in preventing or removing bad tastes and odors from water, and therefore clarifying it, was established experimentally by Johann Tobias Lowitz in 1789-90" (Baker 1981, p. 26). By the end of the 19th century, sand and crushed coal were used to filter drinking water in the United States (Jesperson 1996a). Modern carbon filtration systems first came on the scene in the late 1960s, resulting in the plethora of water filters we have today, including water pitchers, faucet filters, and even water-bottle filters. In 1966, Heinz Hankammer started producing Brita charcoal filters in Germany, naming his company after his young daughter (Clorox Company 2011).

Teacher background information

Materials

For the Engage portion, try to locate a few common household water filters you may have on hand such as those used in filtering water pitchers, refrigerators, water faucets, and coffee pots, or you can search for online images by using a phrase such as "carbon filters." For each group of three to four students, you will need a funnel, several pieces of filter paper, and three small beakers. If funnels and filter paper are not available, you can substitute a half-liter empty water bottle that has been cut in half, with the top inverted and inserted into the bottom to form a funnel and receptacle with a coffee filter inside. In addition, each group will need a 300 mL solution of bleach and water. The dilution students are working with here is very weak, but you should review the material safety data sheet for bleach (Fisher Scientific 2008). …

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