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Students often arrive in our science classrooms with perceptual and conceptual ideas that must be overcome to accommodate a correct understanding.
Perceptual = using the senses to categorize objects in to groups
Conceptual = categorizing objects based on what they do which is inferred from the original perceptual observations.
Melting and solubility are often confused by students. Solubility appears to make things disappear and clear liquids like water often seem to disappear when they undergo the phase change form solid to liquid. Students' perceptual experiences can lead to misconceptions surrounding these two very different physical changes. By undergoing a quick discussion surrounding an inquiry probe designed by Page Keeley I can quickly assess learners' understanding and work through any misconceptions. We can now proceed to investigate how physical properties and changes can help scientist identify unknown substances. I prepare two unknown samples that have similar physical appearance (salt and sugar), in a laboratory station configuration in our classroom.
A pre-laboratory inquiry focuses students’ attention surrounding the physical properties of appearance. We discuss how visual observations are important, but do not allow scientists to prove their hypotheses therefore, scientists must perform experiments with measurable outcomes to support their hypotheses. Station one tests and measures solubility and station two measures time it takes each unknown substance to melt.
In this investigation, solubility does not provide conclusive evidence to support students’ hypotheses because both substance A (salt) and substance B (sugar) dissolve in water. I encourage learners to continue their scientific inquiry much as scientist in the real world do through trial and error methods. At station two, substance B (sugar) melts at a significantly lower melting point than substance A (salt) so students can use this data point to show evidence whether their hypotheses were correct. In this experiment learners gain laboratory experience using their laboratory safety skills and common laboratory equipment. Learners in this activity must think creatively by drawing conclusions. They connect the conclusion directly with the original problem and articulate how the conclusion addresses the problem. Learners must document and justify a position through appropriate inferences.
Flashcard set
Flashcard set
Some learners struggle to understand physical changes and chemical changes. These flashcards may help them review.
Also available on TpT. Melting or Dissolving Card Sort
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