Patricia A. Morrison
Lesson Seven To illustrate types of chemical changes perform two simple demonstrations: burning magnesium ribbon and decomposing hydrogen peroxide using manganese dioxide as a catalyst (and detergent to enhance the visual appearance of bubbles). Write equations on board emphasizing that chemical changes produce new substances. Students will note the signs (what they actually observed) of a chemical change recalling previous experiments as well as those just witnessed: production of lots of heat and light energy, formation of bubbles, formation of a precipitate, and change in color of an indicator. Class will end with a brief lecture defining chemistry, matter, mass, substance, physical change and chemical change.
Assignment: Read text pp. 44-45, 234-237. Add vocabulary words to running list. Write a paragraph explaining how the painting exemplifies the definition of chemistry, physical change and chemical change. Note the words "reaction" and "change" are often used interchangeably. Be clear and specific. Remember English usage counts.
Lesson Eight Discuss students' examples of chemical and physical changes and how they thought the painting illustrated "chemistry." The primary forms of energy produced are heat and light. The major physical change occurs as the blacksmiths reshape pig iron into useful implements; the major chemical change involves burning. Students should deduce (or should have deduced) that the blacksmith is burning wood or perhaps coal, and that the bellows provides additional oxygen to make the fire burn hotter.
Introduce tomorrow's lab, which will focus on physical change. Mix different substances together in front of students at the beginning of class. Students will have to separate these substances. Substances that are merely physically mixed together can be physically separated based on their properties.
Assignment: Read text pp. 37-39, 46-50.
Lesson Nine Laboratory Experiment on Separating Mixtures
Reiterate that physical changes do not produce anything new and, therefore, often can be undone physically. Iron that is shaped into one form can be reshaped into another. Give groups of three students five samples of physical mixtures to separate. Equipment in the room includes test tubes, funnels, beakers, filter paper, magnets, centrifuge, hot plates, and condensation tubes. Students may request any additional equipment that is available. The mixtures include:
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Sulfur and iron filings
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Salt and sand
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Red food coloring in water
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Catsup in water
Assignment: Complete lab write-up using skeleton format handed out in class. Explain how you separated each mixture. If you did not have time to finish separating each mixture, which is quite likely, explain how you would separate it. Try to use the proper name for each separation procedure.
Lesson Ten Review lab with distillation apparatus assembled. On the board, list methods of separation: filtering, evaporating, distilling, using magnet, using centrifuge. (Students may add decanting and chromatography based on their reading.) Indicate the physical properties that made separation by this method possible. The properties of substances determine the methods used to separate them. Just as reactions can be physical or chemical, so can properties.
By drawing on students' prior knowledge and teacher additions, chart the physical properties, subdivided into qualitative and quantitative, and four major chemical properties: burns, supports combustion, reacts with an acid, doesn't react (inert).
Assignment: Select three substances present in
The Blacksmith's Shop
and list their physical and chemical properties. (Possible substances include: iron, oxygen, water, carbon dioxide, nitrogen and carbon.) Which substances are visible in the painting? Which substances did you deduce were present? What properties can you deduce from the painting? Remember that in chemistry the word "substance" means an element or a compound. Review text pp. 37-39, 48-50 and make certain that your vocabulary list is up to date and that you know all meanings.
Lesson Eleven Quiz on vocabulary, concentrating on physical and chemical changes, physical and chemical properties and methods of separating mixtures.
Again write equations for chemical reactions students have observed. Classify reactions: synthesis, decomposition, single replacement, double placement, neutralization and combustion (deduced from painting). Emphasize identification of reactions by carefully noting if reactants and products are elements or compounds. At a simplistic level one can identify types of reactions by counting and recognizing capital letters, groups, water (H2O) and carbon dioxide (CO2).
Assignment: Study sheet identifying types of reactions. (This topic will be revisited when students study writing and balancing equations.)
Lesson Twelve Reinforce definition of "chemistry": the study of matter, its structure, composition and the energy changes it undergoes. Examine painting from energy perspective. List kinds of energy illustrated in painting: heat, light, potential, radiant, electromagnetic, gravitational, kinetic (implied), and chemical (implied). Add any other types of energy they can recall: nuclear, electrical. Discuss potential energy (stored energy or positional energy) and kinetic energy (energy due to motion, K.E. = ½ mv2) as general terms. Classify all energy into four categories: kinetic (heat, mechanical), gravitational potential, electromagnetic (electricity, magnetism, radiant, chemical, light,) and nuclear.
Assignment: Rd. Text pp. 40-43. Rd. handout: Richard Feynman's essay on energy.
Lesson Thirteen Answer any questions on energy readings. Emphasize energy as a form of matter and the Law of Conservation of mass-energy, E=mc2. Return to painting and look at transformations of energy taking place. Have students give specific examples:
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chemical to heat
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chemical to light
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chemical to gravitational potential
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gravitational potential to kinetic
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kinetic to ?
When you hit an iron bar, where does the energy go?