Teens learn chemistry by creating slime


January 04, 1993|By Anne Haddad | Anne Haddad,Staff Writer

A little monkey business helps soften the inevitable confrontations with Avogadro's Number and the Periodic Table of Elements.

But just because students are mixing a batch of toy slime and burning plastic soda bottles in chemistry class doesn't mean they're goofing off, said Westminster High School junior Brian Parker of Finksburg.

"You'll learn something from it," Brian assured an observer as the lab for burning bottles ended and the one for making the slime began in Alan DeGennaro's class.

Students say Mr. DeGennaro has a knack for making chemistry fun and interesting.

Mr. DeGennaro's peers throughout the state also think highly of him, and selected him secondary science teacher of the year last fall.

His famous "Monday demos" begin each week. He performs feats of chemistry that catch students' attention and teach something, too.

For example, he once dipped pennies into different solutions to turn them "silver" and "gold," said sophomore Bobby Mock of Gamber of the lesson, which demonstrated chemical reactions. "He puts it at your level," Bobby said.

Classmate Brooke Cavey of Silver Run agreed. "I've never really understood science before," Brooke said, "but he explains it, and I even had an 'A' last quarter."

The Avogadro Number, by the way, is a standard chemical measurement that is the number of molecules in a mole of any substance, or 6.0225 times 10 to the 23rd power. Subjects like that may merit breaking away for a little fun now and then.

The 19th century chemist for whom the measurement is named might scoff at what students were doing in Mr. DeGennaro's class the day before winter break. The lesson was to produce a homemade version of Gak, a slimy substance made by Mattel that feels like a cross between Silly Putty and Jell-O.

Before turning the students loose to mix the simple ingredients, Mr. DeGennaro held up a quart of Elmer's Glue and asked if anyone knew what the white adhesive was made of.

"Horses," said one student.

"No. It's made by the Borden Company," Mr. DeGennaro hinted. The glue is made from solids removed from raw milk before it is processed.

The molecules in the solids form long strands of proteins.

"These protein chunks in milk bump up against each other. That's why they don't flow like water," he said, demonstrating with a few pieces of cotton string on the overhead projector.

Pulling the strings together, he explained that a borax solution, another ingredient in the Gak the class was going to make, links the milk proteins together into a netlike structure, making the mixture more like a solid.

While Gak is made with milk proteins, Silly Putty is made much the same way with petroleum products, Mr. DeGennaro told the class.

The students then lined up to follow the Gak recipe. They measured glue into a small paper cup, then added the borax solution and talcum powder and their choice of food coloring. They stirred with a wooden stick.

Within a few stirs, the contents of the cup separated into a pliant lump and a thin liquid. Students poured the liquid down the drain, then took the brightly colored lumps out and kneaded them, bounced them, flattened them, stretched them and generally seemed to have a good time.

Mr. DeGennaro encouraged the students to test the slime, but asked them not to throw it at each other.

The printed recipe the students received challenged them to consider the properties of Gak and whether the product is a liquid or a solid.

"I'd say liquid," Brooke told a classmate, referring to a rule of chemistry about liquids: "It takes the shape of things."

As the class ended and the students left to begin their two-week holiday, Mr. DeGennaro reflected on how his teaching style has changed since his first job 17 years ago at Wilde Lake High School in Howard County.

"The conventional wisdom just says you have to focus the students' attention.

You ask the leading questions and relate it to things they know from before," he said.

"I know I have not taught them the size of molecules and how things flow, but this is a close approximation. They'll go home and talk about this."

After the holidays, he said, "I'll try another lab, and by the end of the year everyone will understand."

Not all of his students are as enthusiastic as he would like, he said, and not all of them will remember his lessons for the rest of their lives.

"When those students walked out today, I couldn't really know how many of them understood it or how much they got out of it," he said.

"We don't see our results right away.

"One of the benefits of the job is that every kid is different, but that's also the curse," he said.

The most frustrating part of public education, he said, is teaching to a mass audience.

"We run out of time. Kids are absent. They come in and need yesterday's work.

Some kids who are gifted get bored. Some kids are hopelessly challenged," he said.

Mr. DeGennaro said he had a good opportunity to get out of teaching, and decided to stay.

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