ISM_chapter5_part1

ISM_chapter5_part1 - Chapter 5 Chemical Reactions 169...

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Unformatted text preview: Chapter 5: Chemical Reactions 169 Chapter 5: Chemical Reactions Teaching for Conceptual Understanding In Chapter 4, students learned how to balance equations. In Chapter 5, the concept of net ionic equations is introduced, and the student must now also be reminded to balance the charges, as well as the atoms. Teach students to chunk information when possible, i.e., balance polyatomic ions as a whole unit instead of individual elements. Once students master balancing chemical equations, do not assume they will have mastered net ionic equations. Along with the common misconceptions described in the introduction to Chapter 4, students will now start confusing what is an ion and what is a molecule. For example: • the notation 2 NaOH(aq) is thought to form Na 2 and OH – or a molecular compound where O is the central atom and 2 Na and 1 H are bonded to it. • the notation H 2 SO 4 (aq) is thought to form an H 2 molecule and SO 4 2– ion, or maybe an S atom and 2 O 2 molecules. Reinforce the notion that when an ionic compound becomes aqueous, the common ions of which they are composed are recreated. Refer the students back to Chapter 3 (especially Figure 3.2 and Table 3.7) when they make mistakes. When teaching redox chemistry, do not limit the topic to the loss or gain of electrons. Biological applications of redox chemistry focus more on the loss or gain of oxygen, and the loss or gain of hydrogen. Important new stoichiometric relationships are introduced in this chapter. Figure 5.17 on page 199 shows how all of the stoichiometric relationships interrelate. You may want to use this as an overview and then highlight each individual portion as you introduce it or work sample problems. Molarity, while seemingly simple, tends to be a point of confusion for many students. Because the concept of concentration is so important, make sure that the students are capable of doing problems that relate both to dilution and to volumetric reactions. Warn the students that the dilution equation described on page 195 should NOT be used for reactions. Evaluate their abilities to do volumetric calculations with stoichiometric coefficients that are different from one. Suggestions for Effective Learning Most students start learning about acids and bases back in middle school science classes. Have them tell you everything they know then use your class time more wisely by clarifying and expanding on their knowledge. Don’t use the notation HOAc for acetic acid. Ac is the symbol of the element actinium. Acetic acid is an organic acid and should always be written CH 3 COOH. Demonstrate acid and base strengths with a conductivity apparatus. Samples of 0.1 M HCl, CH 3 COOH, and NaOH, and aqueous NH 3 work well....
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ISM_chapter5_part1 - Chapter 5 Chemical Reactions 169...

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