“When water is heated, it changes into something new … steam.”
“Chocolate can melt and be frozen again.”
“I think volcanoes can change rocks underwater.”
When posing such an open question as “what ways does matter change?” its easy to see the range of understanding and swath of misconceptions surrounding matter. But with the expectation that students will be able to “conduct an experiment to determine whether the mixing of two or more substances results in new substances with new properties,” Pine Glen’s, Sarah Visocchi kindly offered to volunteer her class as a guinea pig setting to do just that.
Our week long curriculum was framed with a multitude of student learning goals in mind. Besides coming up with the framework of an experiment exploring whether water and sodium polyacrylate forms a new substance (see day 5 below) students were expected to ultimately understand how “the addition or subtraction of heat energy can lead to phase changes” as outlined in current MA science standards and provide reasoning through evidence as to why a physical or chemical change has occurred. (See our backward design outline for the curriculum here or in the resources link at the bottom of the post.)
Our investigation began with a dialogue and recording of students’ current understanding of how matter changes. When posed the question directly to start the day, most came up with physical changes such as melting, freezing or an object changing shape as a result of a new container or force acted on it. Basic definitions of physical and chemical changes were provided along with a model of matter as particles. Students then completed a pre-assessment asking for best guesses as to which type of physical and chemical changes were which. The class was then polled, and examples that were unanimously voted physical or chemical were marked while inconclusive changes were given a question mark label. For unanimous changes, students reasons for why they said what they did were recorded on a classroom table to be referenced and checked for correctness through the rest of the week.
|Physical or chemical changes? Are new substances formed?|
Brought us to our first series of investigations and observations. Hot plates were brought in along with six different forms of matter. Each student was given a changes in matter investigation foldable notebook that was used for the rest of the week. Water, chocolate, quartz crystal, kool-aid, salt water, and pancake mix. Heat was applied to all six (three at a time) and observations were shared and recorded as changes occurred. There was some debate about whether the “smoke” or “steam” rising from the water was a new substance. Students also recognized the steam to be similar to what began to rise from the salt water and kool-aid in the second shift of investigations. Many students correctly predicted that if more heat was added to the quartz it would likely “melt” like the chocolate and ice had.
After all the investigations were completed, a round of reflection was completed in the circle and key terms such as “evaporation, condensation, melting and freezing” were emphasized and discussed further. Once again class notes were taken on a board describing which changes suggested physical changes and which suggested chemical changes. It was defined that physical changes are simply when a matter changes its form but does not form a new substance while chemical changes created new substances. These terms and definitions were used frequently from then on to emphasize the connection between the two and whether new substances had been made or not.
Class began with groups of students sharing observations and answers to questions with the class about each station before our final investigation began. Plastic dishes were handed out along with a powdery white substance for students to observe with magnification lenses. Once initial observations were completed students were taught how to use eyedroppers (after seeing less than exemplary use on Day 3!) and water was added to the mystery substance. Students watched in amazement as the powders surprisingly expanded to three or four times their original size! Not all students were stunned… some were familiar with the science trick “instant-snow” and recognized the powder to be the same used in diapers, a substance known as sodium polyacrylate.
|Sodium polyacrylate is the same chemical found in diapers for its liquid-absorbing properties|
Students were then posed the question: Has a new substance been formed? How can you tell? Ultimately this led to a brainstorm session about how the students could experiment with the water-logged powder to determine if a new substance had in fact, been made. Predictions and possible experiment forms were shared via email and in some cases (such as leaving the powder out by the window over the weekend) were conducted before the final day’s experiment.
With many shared experiment methods centered around the importance of adding heat (success!) to determine if new substances had been made or if mixtures of matter might separate, a final investigation was brought to the class involving a hot plate and a closed system consisting of two flasks connecting with rubber tubing. Students were immediately fascinated with the setup and excited to see if the tube and rubber stoppers would “capture” the steam and leave it available for further testing to see if it was water or would recombine to form the new powdery white matter. As many expected, a clear liquid began to collect at the bottom of the second flask. Was it water or something else? Students wondered. One suggested we “see if it freezes.” An excellent suggestion and one that showed we had had at least some success with our goal. After roughly 15 minutes of heating the new liquid was collected and placed in the freezer to be observed later. Mrs. Visocchi had students return to the original pre-assessment and review their answers to see if they would consider making any changes…
Overall, both Sarah and I were pleased with the amount of engagement and interest in the investigations and the amount of scientific conversation each generated. Students struggled with self-correcting some of the pre-assessment questions and I wondered if the terms “physical” and “chemical” changes simply got in the way of some students. In the future I anticipate narrowing the focus of the investigations to simply whether or not new substances are formed and what kind of changes suggest yes or no, eliminating a layer of vocabulary for emerging language learners, students with language disabilities, and so forth. The notebook helped students carry their observations throughout the week and the ability to check back on previous investigations. More importantly the class-wide record of what kinds of changes were physical and chemical (and therefore indicated new substances) was critical and used frequently to check for understanding and misconceptions. This tool was particularly valuable in our school system as the new ELA writing pilot uses similar tables when writing about non-fiction and provides valuable opportunity for skill overlap. Sarah affirmed by belief that this form of matter exploration was “far better” than previous rehashes of solid, liquid and gas properties and led student to deeper understanding than old observations of density columns and blowing up balloons. Oobleck was still included though during a science period unsupervised by me… a favorite activity for persuasive arguments through evidence of whether the matter is a solid or a liquid!