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Setra Variable Capacitance Scale Helps High School Chemistry Students Get Balanced Education


When a high school chemistry teacher and a lab assistant decided to completely reconfigure their laboratories, they had a sizeable job on their hands-a very miniscule size to be exact.

Carol Murphree, chemistry teacher at Acton-Boxborough Regional High School in Massachusetts, and Charlene Golden, the department's laboratory assistant, determined a few years back that they needed to rewrite their lab experiments to function on a micro scale - that is to incorporate experiments that feature very small quantities of chemicals. This dramatic shift would require substantial planning, as well as the procurement of new lab equipment. But they deemed it to be an essential change for a number of reasons.

One reason was the natural concern for safety that arises when a large class of teenage students is working with a large number of potentially volatile chemicals. Smaller amounts of each chemical would inherently be safer. There was also a concern for the greater environment and a desire to reduce the problem of chemical disposal. And of course, as with just about every high school in the country, this Massachusetts high school was dealing with budgetary constraints. The cost of chemicals is steadily increasing. Murphree felt that her department could reduce costs by conducting some experiments with smaller amounts of chemicals.

Murphree, who teaches both Introductory Chemistry and Advanced Placement chemistry, explained the thinking behind the selection of one particular piece of equipment.

She said, "Charlene and I discussed all the variables that would go into rewriting our labs to function on a micro scale, and we visited a number of different high school labs to see how they addressed the issues we were facing. One concern we had was the inadequacy of our existing balances. It was clear to us that we needed new balances that would provide us with a greater degree of precision and accuracy. My A.P. students, in particular, are constantly pre-weighing chemicals for experiments, and then weighing them again to determine the precise amount of change. Their viable experimental results hinge on the accuracy of the weighing equipment, even more so when they are working with such miniscule quantities."

Locating a balance with this level of precision and quality might normally pose a challenge. Fortunately, Acton-Boxborough Regional High School didn't have to look very far. Based right in Boxborough, MA, Setra Systems is a leading designer, developer and manufacturer of electronic instrumentation for measuring pressure, acceleration and weight. Setra's Sierra Series SI-410S laboratory balances were an exact match for the chemistry department's specifications.

Setra's Sierra Series of precision balances includes four single range models (S Models), including the SI-410S, and two dual range models (D Models). The SI-410S series offered a number of advantages over the high school department's old balances. For one thing, the Setra balances are designed to weigh much smaller amounts, as they can weigh up to three decimal places; the old equipment could only measure up to two places.

Another key benefit - the SI-410S automatically displays the maximum resolution whenever the balance is tared, regardless of how much weight is zeroed out. For instance, the 0.0001g resolution of this precision balance is available up to 100 grams, even when a user tares objects that weigh close to the balances' rated capacity.

For maximum accuracy, the SI-410S also provides the unique advantage of Setra's patented variable capacitance sensing technology. This technology delivers maximum reliability while requiring fewer parts, so the balances remain structurally streamlined, inside and out, while taking up less valuable lab space. This is especially important in a relatively small high school chemistry lab.

The SI-410S has other benefits that are particularly relevant to Murphree's students.

She explains, "It all comes down to making it easier for students to get better laboratory data. First, the heightened accuracy greatly reduces the potential for errors in an experiment. The balance's wind-shield is also an excellent feature. When kids walked by our old balances, any little bit of breeze would cause the balance to oscillate. The wind screen eliminates this variable. "

The simplicity of the SI-410S is also a plus. This balance has one standard weighing mode - grams. So, according to Murphree, "the students don't have to think twice about the weight mode, and there's no danger of pushing the wrong button and accidentally switching to a different mode."

Two Setra balances are used just about every day at Acton-Boxborough High. Lab assistant, Golden, uses one balance every time a particularly dilute liquid or solid needs to be prepared for an upcoming experiment.

"The balance is essential when I need, say, .057 grams of a particular material," she explained, "or when I need trace amounts of various chemicals, as I do a couple times a year when I make up artificial urine for a biology class."

The second balance is used constantly by Murphree's students, particularly those in her AP class. "I'd say it is being used most mornings at least four days a week," she said.

Murphree gives an example of a recent experiment that couldn't have achieved success without the SI-410S. Her AP class was charged with determining the molar mass of a volatile organic liquid. None of the students were told the nature of their liquid - there were actually five different liquids, ranging from acetone to hexane.

She explained, "The students would have to vaporize the liquid in a warm water bath to condense it, and then weigh the miniscule volume that remains. This amounted to usually less than a gram, so the balance's ability to weigh to three decimal places made a big difference in the accuracy of the results."

Overall, the results of the high school students having access to a balance with the precision and quality of the Setra SI-410S have been uniformly excellent.

Murphree concludes, "It's a pleasure to be able to offer my students the best instruments available. As I said before, it's all about achieving accurate results. It's important for our students to know that the experimental value they are seeing is in fact the real value. The Setra balance makes this happen."

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