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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Content Panel Report: Chemistry
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools 1 Introduction The National Research Council’s Committee on Programs for Advanced Study of Mathematics and Science in American High Schools (parent committee) formed a chemistry panel to compare and evaluate the Advanced Placement (AP), the International Baccalaureate (IB), and alternative programs for advanced study in chemistry with respect to their pedagogy, content, assessments, and outcomes (the charge to the panel is presented in Appendix A). The chemistry panel met twice (in June and July 2000) to address its charge from the parent committee. The panel was chaired by a member of the parent committee, who served as liaison to the committee and consolidated the panel’s findings and recommendations into this report. Panel members also included high school chemistry teachers with AP, IB, and New York State Regents examination experience, along with experienced college and university chemistry professors noted for their work in chemical education (for biographical sketches, see Appendix B). Neither independent researchers nor the AP or IB program has published systematic data about the programs. Thus few data on the ways in which AP and IB courses are actually implemented in U.S. high schools, the long-term consequences to students who take AP or IB courses, or the effects of an increasing number of students who arrive at college with multiple AP and IB credits to use toward advanced placement or to meet graduation requirements were available to the panel. Because important data about the programs have not yet been published by either the programs or independent researchers, the panel focused its analysis on what the programs say they do, using available program materials such as course guides, released examinations, teacher manuals, program goals, and mission statements. The chemistry panel carefully reviewed a substantial volume of background materials related to the AP and IB programs; those materials are listed in Appendix C. The findings and recommendations reached by the panel and presented in this report were consensus opinions, arrived at by reading the background materials and holding extensive discussions. Panel
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools members also contributed written materials that were incorporated into this final report. The remainder of this report is divided into four chapters. Chapter 2 presents an overview of advanced study in chemistry for high school students. Chapters 3 through 5 respond to the questions under the panel’s charge. Chapter 3 focuses on the students who enroll in the AP chemistry course and the IB program, what is taught and how well it is being taught, the grade levels at which these advanced courses are offered, and the background and prerequisites needed to take and succeed in the courses. Chapter 4 addresses those who teach AP and IB chemistry courses, including their academic preparation, credentials, and appropriateness for the task. Chapter 5 provides an analysis of the assessments and outcomes associated with the AP chemistry course, the IB chemistry program, and their affiliated examinations. Throughout these chapters, key findings appear in italic type. The report concludes in Chapter 6 with a summary and recommendations regarding the AP chemistry course and the IB program, including the panel’s consideration of whether advanced study options in high school should be associated with opportunities for students to earn college or university credit.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools 2 Overview of Advanced Study Programs in Chemistry in U.S. High Schools CHARACTERISTICS OF AP CHEMISTRY In addition to recommending that at least 290 minutes per week be allotted to Advanced Placement (AP) chemistry courses, the College Board characterizes the AP chemistry course as follows: The AP chemistry course is designed to be the equivalent of the general chemistry course usually taken during the first college year. For some students, this course enables them to undertake, as freshmen, second-year work in the chemistry sequence at their institution or to register in courses in other fields where general chemistry is a prerequisite. For other students, the AP chemistry course fulfills the laboratory science requirement and frees time for other courses. AP chemistry should meet the objectives of a good general chemistry course. Students in such a course should attain a depth of understanding of fundamentals and a reasonable competence in dealing with chemical problems. The course should contribute to the development of the students’ abilities to think clearly and to express their ideas, orally and in writing, with clarity and logic. The college course in general chemistry differs qualitatively from the usual first secondary school course in chemistry with respect to the kind of textbook used, the topics covered, the emphasis on chemical calculations and the mathematical formulation of principles, and the kind of laboratory work done by the students. Quantitative differences appear in the number of topics treated, the time spent on the course by students, and the nature and variety of experiments done in the laboratory. Secondary schools that wish to offer an AP chemistry course must be prepared to provide a laboratory experience equivalent to that of a typical college course (College Entrance Examination Board [CEEB], 1999a, p. 1).1 (Note: Italics added for emphasis by the College Board.) 1 These publications are commonly referred to as Acorn Books because of the distinctive logo on their covers.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Thus by design, AP chemistry courses (and all other AP courses) are modeled after typical college-level introductory courses in the discipline. As a result, these high school courses are supposed to follow trends in college-level introductory general chemistry (not introductory chemistry, which typically denotes remedial or nonscience major chemistry courses). The College Board goes on to say that: The AP chemistry course is designed to be taken only after the successful completion of a first course in high school chemistry. A survey of students who took the 1986 AP Chemistry Examination indicates that the probability of achieving a grade of 3 or higher on the AP Chemistry Examination is significantly greater for students who successfully complete a first course in high school chemistry prior to undertaking the AP course. Thus it is strongly recommended that credit in a first-year high school chemistry course be a prerequisite for enrollment in an AP chemistry class. (CEEB, 1999a, p. 1)2 (Note: Italics added for emphasis by the College Board.) Whether schools offering AP courses follow this recommendation probably depends on local practice. In any case, the chemistry panel unanimously agrees that, unless truly exceptional circumstances dictate, students should not take advanced chemistry as their first chemistry course in high school.3 Although the College Board also recommends against this practice, it does happen, and the panel believes it is detrimental to the student, who is academically short changed by such circumstances. It is in the first course that the requisite concepts are learned and the laboratory skills developed that are needed to legitimize advanced study in the second high school chemistry course.4 An appropriate background in mathematics is needed to succeed in AP chemistry, and the College Board addresses this matter as well: “In addition, the recommended mathematics prerequisite for an AP chemistry class is the 2 The College Board (2001b) reports that in 2001 of the 55,000 students taking AP Chemistry, 3,000 were in the ninth or tenth grades, and 28,000 were in the eleventh grade. However, it is unclear from these data what percentage of students take AP Chemistry as their first course in the subject. Of the 28,000 students in the eleventh grade taking AP Chemistry, it is possible that many or most of them took introductory chemistry in the tenth grade. Additional research is needed to determine the actual proportion of students who take AP Chemistry as their first course in the subject. 3 Exceptional circumstances that would enable some students to succeed in an advanced course in chemistry as their first exposure to the discipline could include students who have had unusual preparation in science and mathematics or who have proven that they can acquire the concepts taught in introductory chemistry on their own. The panel emphasizes that such exceptions would be made only in very rare cases. 4 There are few data on the extent to which this practice occurs. The panel believes that gathering such data is important and calls on the College Board to gather and publish data describing the ways in which their courses are implemented in schools and the effects of those courses on student learning and achievement.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools successful completion of a second-year algebra course” (CEEB, 1999a, p. 1). (Note: Italics added for emphasis by the College Board.) The College Board also is explicit regarding the place of AP chemistry in the total science curriculum: “The advanced work in chemistry should not displace any other part of the student’s science curriculum. It is highly desirable that a student have a course in secondary school physics and a four-year college preparatory program in mathematics” (CEEB, 1999a, p. 2). Because of the structure of the AP program, the AP chemistry course can be a stand-alone course offered by a high school in the absence of any other AP course offerings at that high school or other high schools in the district. Moreover, students who enroll in and complete AP chemistry, or any other AP courses, are not required by the College Board to take the AP examination developed by the College Board and administered by the Educational Testing Service.5 Administered each May, the AP chemistry examination takes 3 hours and consists of 2 sections. The first section (90 minutes) consists of 75 multiple-choice questions and represents 45 percent of the final grade. The College Board uses some common multiple-choice questions from year to year as a consistency check on the performance of the students taking the exam. The second section of the examination (also 90 minutes) represents 55 percent of the final grade and consists of several short-answer and essay-style questions that purportedly provide for a more in-depth assessment of students’ understanding of chemistry principles. The questions may require calculations, a short essay response, or the determination of reaction products. Section II contains both required questions to which all students must respond and opportunities for students to choose two of four additional questions that they think they are best prepared to answer.6 The examinations are collected and sent to a central location, where they are graded by a national team of graders.7 All of the examinations are graded during a 1-week period. The College Board has developed procedures to ensure uniformity in the scoring process.8 The AP score (1–5) is determined by a complex formula that factors in how well others who took the test performed, how scores were distributed over the past 3 years, and how well college 5 Although the College Board has no such requirement, some state and local school districts are now requiring students to take the examination. In these circumstances, the district or state sometimes pays for part or all of the costs to students of taking the exams. 6 For example, in 2001 the AP Chemistry examination required that students answer questions 1, 4, 5, and 6 and allowed them to choose between questions 2 and 3 and between questions 7 and 8. 7 Graders are drawn from a pool of experienced high school AP teachers and college faculty with expertise in the discipline. Individuals are nominated or apply to become graders. 8 For example, more than one grader reads each paper, and large discrepancies between assigned scores are resolved by third and sometimes fourth readers.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools students at the end of their introductory course performed on the AP examination. CHARACTERISTICS OF THE IB PROGRAMME AND IB CHEMISTRY Whereas the AP program is a collection of individual, unrelated courses, the International Baccalaureate (IB) Diploma Programme is a comprehensive 2-year curriculum consisting of six academic areas.9 IB courses may be taken at either the Standard Level (SL) or Higher Level (HL).10 Chemistry is included with Group 4, the Experimental Sciences. IB Diploma candidates must take one subject from each of the six subject areas, with at least three and not more than four being HL. The other courses taken are SL. Thus, a chemistry student can take either the HL or SL version of the IB chemistry course and related examination. IB students are permitted to take two science subjects simultaneously from Group 4. Students can and do take individual IB courses without working toward an IB Diploma. These students are known as certificate candidates, as opposed to diploma candidates. Only diploma candidates are required to take one subject from each area, as well as to fulfill additional requirements. Approximately 65 percent of IB students work for and complete the requirements for a diploma. IB Diploma candidates must also complete three other requirements: (1) the interdisciplinary Theory of Knowledge course; (2) an extended essay of approximately 4000 words; and (3) participation in the school’s Creativity, Action, Service (CAS) program involving sports, artistic pursuits, and community service work. Unlike the AP program, the IB program seeks to provide interdisciplinary preparation for university work rather than attempting to meet particular university course requirements, although strong perfor- 9 Although AP courses are not traditionally offered as an integrated program, the panel notes that for several years the College Board has offered an International Diploma for Advanced Placement. This program is designed for students who plan to pursue undergraduate studies outside the United States or Canada. The total number of students seeking this diploma is relatively small. To earn the diploma students take four AP courses in three different subject areas and must receive an average grade of 3 or higher. In 2000, the College Board initiated a pilot test of a new AP Diploma that is similar to the IB Diploma in many respects. To qualify for this diploma, students must take one AP course from each of the following areas: languages and literatures, sciences, mathematics, history, and social sciences. They must also take one additional AP course in any area. In addition, students must earn an average grade of 3 on all exams taken. Additional information is available at http://www.collegeboard.org/ap/students/benefits/int_diploma.html [4/24/02]. 10 SL courses entail 150 hours of class time, while HL courses require 240 hours. HL courses are generally taught over 2 years.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools mance in IB courses is used to grant advanced placement at colleges and universities (International Baccalaureate Organisation [IBO], 1999). All Group 4 subjects include required practical (laboratory) work, which makes up a significant portion of the course.11 Although this laboratory work focuses primarily on the assessment of laboratory skills, it also offers opportunities for students to perform experiments and experience first-hand the benefits and limitations of scientific methodology. Individual teachers plan the Practical Scheme of Work (PSOW) for students in their classes. Thus, the laboratory experiences of students in different IB classrooms will vary. The PSOW should represent the breadth and depth of the subject syllabus, but students are not required to conduct an investigation for each topic in the syllabus. To ensure quality and to foster improvements, teachers are required to submit copies of their PSOW annually to the IBO for moderation and feedback. As noted above, the College Board recommends that at least 290 minutes per week be allotted for an AP chemistry class (174 total hours per year, assuming a 36-week academic year). Of this total, 54 hours is recommended for laboratory work. By comparison, IB recommends a total of 240 hours for HL and 150 hours for SL courses per academic year. Of this time, it is recommended that 60 hours for HL courses and 40 hours for SL courses be devoted to investigative activities that, along with the Group 4 project, comprise the internal assessment (IA) component of the course. A common core curriculum applies to both HL and SL chemistry courses. The core material taken by SL students is a subset of the HL program. At the SL level, the core topics make up about 60 percent of the material, while at the HL level the core represents 75 percent of the covered topics. Both SL and HL students also study optional topics that their teacher selects from among a list of topics included in the course syllabus. SL students study three options of 20 hours each, while HL students study two options of 30 hours each chosen by the school. The only option available exclusively to SL students is higher physical organic chemistry (15 hours). Options available to both SL and HL students (15 and 22 hours, respectively) include medicines and drugs, human biochemistry, environmental chemistry, chemical industries, and fuels and energy. The options available to HL students only (22 hours) are modern analytical chemistry and further organic chemistry. Additional hours of internally assessed practical work are required for both SL and HL options.12 Further, both SL and HL students must spend 10–15 11 The IBO recommends that 25 percent of the course be devoted to practical (laboratory) work. 12 SL options require an additional 5 hours of practical work that is internally assessed; options that are suitable for both SL and HL require an additional 5 hours for SL students and 8 hours for HL students; and options exclusively for HL students require 8 hours of internally assessed practical work.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools hours on an interdisciplinary Group 4 project, which is a common element of all IB science programs and constitutes 10 hours of the internally assessed practical scheme of work.13 The IB chemistry examination is given annually and is taken at either the SL or HL, depending on the student’s course of study. The SL exam consists of three papers. The first paper (0.75 hour) consists of 30 multiple-choice questions. The second paper (1 hour) contains short-answer questions and brief calculations in Part A and offers students a choice of answering one of two more extended questions in Part B. The remaining paper (1.25 hours) consists of one or two questions based on the course options completed by an individual student. The HL examination also comprises three papers with the same distribution as that of the SL examination but with topics examined in greater depth. The time allotted for the first HL paper is 1 hour, for the second 2.25 hours, and for the third 1.25 hours. IB examinations are sent to examiners around the world who mark and return them to the IBO offices in Cardiff, Wales. During the grading process, examiners measure each student’s performance against seven grade descriptors, given in the form of levels of performance that candidates can demonstrate on the examination. To ensure uniformity in the grading across examiners who are not centrally located, a representative sample of graded examinations from individual examiners is sent to the chief examiner for moderation. IB examination grades (1–7) are based on established criteria that represent an absolute standard of quality; thus, the interpretation of a student’s performance is criterion referenced. A grade of 7 represents “excellent performance,” while grades of 4 and 1 represent “satisfactory” and “very poor” performance, respectively. All IB group subjects, including chemistry, have a significant IA component involving laboratory work and a project, which constitutes 24 percent of a student’s final grade. The IA component is internally assessed at the student’s school by the teacher and is also externally moderated by the IBO. Final IB scores for each student are a combination of the results of the IA and the external scoring of the examination papers but are reported to the school as a single total. QUALIFICATIONS FOR TEACHING ADVANCED HIGH SCHOOL COURSES IN CHEMISTRY To provide a chemistry course consistent with the criteria noted above for an advanced study course in chemistry at the high school level, those 13 The Group 4 project is an interdisciplinary activity that involves all of the IB science students at the school in identifying and investigating an issue, usually of local interest. The project requirements emphasize sharing concepts and theories from across the disciplines and the processes involved in scientific investigation, rather than producing products.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools who teach such a course must be adequately prepared. The chemistry panel takes this to mean a B.S. or B.A. degree in chemistry and preferably an M.A. or M.S. degree in chemistry. The preparation of AP and IB chemistry teachers is discussed in detail in Chapter 4. DEFINITION OF ADVANCED STUDY IN CHEMISTRY FOR HIGH SCHOOL STUDENTS The chemistry panel agrees that the prerequisite first-year high school course in chemistry should provide students with an introduction to the atomic-scale view of matter, including its connection to macroscopic physical and chemical properties and to the language used to express these relationships, using the periodic table as an organizing entity. Moreover, as befits the nature of chemistry as an experimental science, the introductory (first-year) course should include experimentation and the use of scientific methodology. Members of the panel also agree that any high school course in chemistry that is labeled as advanced study, whether or not it is structured according to an established curriculum and assessment such as AP or IB, should enable students to develop the ability to explore the chemistry concepts and laboratory practices introduced in the first-year course in greater depth and, where appropriate, to conduct some form of research. Under the guidance of a qualified advanced study instructor, desirable features of such advanced study would include some combination of the following characteristics: Application of basic ideas to more complex materials, systems, and phenomena Use of modern instrumentation, methods, and information resources Integration of concepts within and between subject areas, including extensions to other disciplines Use of appropriate mathematical and technological methods Extended use of inquiry-based experimentation Development of critical thinking skills and conceptual understanding Use of appropriate tools for assessing student performance and attitude that reflect current best practices Promotion of communication skills and teamwork These characteristics are consistent with visions for undergraduate education articulated in the National Science Foundation’s (NSF) Shaping the Future (1996) and the National Research Council’s Transforming Undergraduate Education in Science, Mathematics, Engineering, and Technology (1999) reports. These two reports summarize what undergraduate science, mathematics, engineering, and technology courses, including introductory courses
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Appendix D Suggested Modifications of Examination Questions This appendix presents examples of the chemistry panel’s suggested modifications to the questions on the Advanced Placement (AP) chemistry 1999 examination, Section II, to make the questions more contextual; to probe more carefully the depth of student understanding; to seek to assess higher-order thinking skills; to require the applications of chemistry principles in an enlarged or new context; and to enjoin students to link concepts to chemical systems and macroscale phenomena, not merely see chemistry principles as isolated facts. In particular cases below, the original question is given, followed by its suggested modification. AP CHEMISTRY 1999, SECTION II, PART A, QUESTION 1 Original Question NH3(aq) + H2O(l) ↔ NH4+(aq) + OH−(aq) In aqueous solution, ammonia reacts as represented above. In 0.0180 M NH3(aq) at 25°C, the hydroxide ion concentration [OH−] is 5.60 × 10–4 M. In answering the following, assume that temperature is constant at 25°C and that volumes are additive. Write the equilibrium-constant expression for the reaction represented above. Determine the pH of 0.0180 M NH3(aq). Determine the value of the base ionization constant, Kb, for NH3(aq). Determine the percent ionization of NH3 in 0.0180 M NH3(aq). In an experiment, a 20.0 mL sample of 0.0180 M NH3(aq) was placed in a flask and titrated to the equivalence point and beyond using 0.0120 M HCl(aq).
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Determine the volume of 0.0120 M HCl(aq) that was added to reach the equivalence point. Determine the pH of the solution in the flask after a total of 15.0 mL of 0.0120 M HCl(aq) was added. Determine the pH of the solution in the flask after a total of 40.0 mL of 0.0120 M HCl(aq) was added. (SOURCE: CEEB, 1999b, p. 42) Suggested Modification The panel would suggest leaving much of question 1 alone, although it could stand to be condensed somewhat. As written, it tests the student’s fundamental understanding of Kb, buffers, and titration stoichiometry. One or more of the following additional questions might be added: Sketch a titration curve for part (e) using the information from (b), (c), and (d) and/or compare the base strength and give the rationale for strength based on the type of site and associated structure for one or two other more obscure bases, given their respective Kb’s. AP CHEMISTRY 1999, SECTION II, PART A, QUESTION 2 Original Question Answer the following questions regarding light and its interactions with molecules, atoms, and ions. The longest wavelength of light with enough energy to break the Cl-Cl bond in Cl2(g) is 495 nm. Calculate the frequency, in s–1, of the light. Calculate the energy, in J, of a photon of the light. Calculate the minimum energy, in kJ mol–1, of the Cl-Cl bond. A certain line in the spectrum of atomic hydrogen is associated with the electronic transition in the H atom from the sixth energy level (n = 6) to the second energy level (n = 2).
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Indicate whether the H atom emits energy or whether it absorbs energy during the transition. Justify your answer. Calculate the wavelength, in nm, of the radiation associated with the spectral line. Account for the observation that the amount of energy associated with the same electronic transition (n = 6 to n = 2) in the He+ ion is greater than that associated with the corresponding transition in the H atom. (SOURCE: CEEB, 1999b, p. 43) (NOTE: On the exam, students were asked to answer either this question or the next question concerning reaction rates, but not both.) Suggested Modification A question containing some of the information assessed in the original version of Question 2 but considerably extended might look like this. This question now relates to a chlorofluorocarbon compound known as CFC-12 or Freon-12. The Lewis structure of the CFC-12 molecule is: [structure would be given] Give the correct chemical name for this compound. Describe the geometrical shape of the compound and estimate the Cl-C-Cl angle. Identify the type of hybridization exhibited by the central carbon atom. The energy of the C-Cl bond is 327 kJ/mol bonds; the energy of the C-F bond is 485 kJ/mol bonds. Explain this difference. or alternatively The energy of the C-Cl bond is 327 kJ/mol bonds. Would you predict the energy of the C-F bond to be higher or lower? Explain your answer. Calculate the frequency, in s–1, of the radiation required to break a C-Cl bond. Calculate the wavelength (in nm) of the radiation required to break a C-Cl bond. Radiation of this wavelength falls within which region of the spectrum? What is the practical significance of the fact that radiation breaks C-Cl bonds in CFCs?
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools AP CHEMISTRY 1999, SECTION II, PART B, QUESTION 4 Original Question Write the formulas to show the reactants and products for any FIVE of the laboratory situations described below. Answers to more than five choices will not be graded. In all cases a reaction occurs. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solution as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. You need not balance the equations. Example: A strip of magnesium is added to a solution of silver nitrate. Calcium oxide powder is added to distilled water. Solid ammonium nitrate is heated to temperatures above 300°C. Liquid bromine is shaken with a 0.5 M sodium iodide solution. Solid lead(II) carbonate is added to a 0.5 M sulfuric acid solution. A mixture of powdered iron(III) oxide and powdered aluminum metal is heated strongly. Methylamine gas is bubbled into distilled water. Carbon dioxide gas is passed over hot, solid sodium oxide. A 0.2 M barium nitrate solution is added to an alkaline 0.2 M potassium chromate solution. (SOURCE: CEEB, 1999b, p. 45) Suggested Modification The panel would like to see the reaction/equation question tied more closely to phenomena and laboratory observation. In each of the cases below, the original version (a, b, c, etc.) and a suggested revision (a′, b′, c′, etc.) are given. (The panel also is not convinced that requiring ionic equations is the most appropriate strategy.) (a) Calcium oxide powder is added to distilled water. (a′) Calcium oxide powder is added to distilled water. Write the equation for the reaction and indicate whether the final solution will have a pH less than, equal to, or greater than 7.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools (b) Solid ammonium nitrate is heated to temperatures above 300°C. (b′) The vapors from 6 M HCl and 6 M NH3 combine to form a white cloud. Write the equation for the reaction. (c) Liquid bromine is shaken with a 0.5 M sodium iodide solution. (c′) 5.0 mL of a 0.5 M solution of sodium iodide is shaken with 5.0 mL of a water solution of bromine and 5.0 mL of hexane, C6H14. Describe what you would observe, and write an equation representing the reaction. (d) Solid lead(II) carbonate is added to a 0.5 M sulfuric acid solution. (d′) 0.5 M sulfuric acid is added to a small quantity of lead(II) carbonate in a test tube. Describe the first thing you would notice, and write an equation representing the reaction. (e) A mixture of powdered iron(III) oxide and powdered aluminum metal is heated strongly. (e′) A mixture of powdered iron(III) oxide and powdered aluminum metal is ignited with a burning piece of magnesium. Sparks, flames, and a pool of molten metal are formed. Write the equation for the reaction. What is the molten metal, and what does this imply about the reaction? AP CHEMISTRY 1999, SECTION II, PART B, QUESTION 6 Original Question Answer the following questions in term of thermodynamic principles and concepts of kinetic molecular theory. Consider the reaction represented below, which is spontaneous at 298 K. CO2(g) + 2 NH3(g) → CO(NH2)2(s) + H2O(l) ΔH°298 = −134 kJ For the reaction, indicate whether the standard entropy change, ΔS°298, is positive, or negative, or zero. Justify your answer. Which factor, the change in enthalpy, ΔH°298, or the change in entropy, DS°298, provides the principal driving force for the reaction at 298 K? Explain. For the reaction, how is the value of the standard free energy, ΔG°, affected by an increase in temperature? Explain. Some reactions that are predicted by their sign of ΔG° to be spontaneous at room temperature do not proceed at a measurable rate at room temperature.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Account for this apparent contradiction. A suitable catalyst increases the rate of such a reaction. What effect does the catalyst have on ΔG° for the reaction? Explain. (SOURCE: CEEB, 1999b, p. 47) Suggested Modification The panel suggests that Section II, Part B, Question 6 of the AP chemistry exam, which deals with thermodynamic principles and KMT concepts, could be directed to higher levels of thinking in part (a) by relating a simple system, such as an ice cube melting, to enthalpy, entropy, and free energy. The student could be asked to explain the process using the above terms and appropriate equations. Part (b) could be similar but related to something common, such as the possible oxidation of sucrose, which has a large negative free energy. The student could discuss why the sugar does not spontaneously combust on the kitchen table since the free energy is favorable. Included in the explanation would be descriptions of the differences between thermodynamic and kinetic stability. AP CHEMISTRY 1999, SECTION II, PART B, QUESTION 7 Original Question Answer the following questions, which refer to the 100 mL samples of aqueous solutions at 25°C in the stoppered flasks shown above (four partially full flasks are shown, each containing an equal volume of 0.10 M solutions of NaF, MgCl2, C2H5OH, and CH3COOH, respectively). Which solution has the lowest electrical conductivity? Explain. Which solution has the lowest freezing point? Explain. Above which solution is the pressure of water vapor greatest? Explain. Which solution has the highest pH? Explain. (SOURCE: CEEB, 1999b, p. 48) (NOTE: On the exam, students were asked to answer either this question or the next question concerning principles of chemical bonding and molecular structure, but not both.)
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Suggested Modification The panel suggests the following modified question: Modification 1. Do not have all solutions be 0.10 M. Instead use 0.010 M NaF, 0.050 M MgCl2, 0.10 M C2H5OH, and 0.20 M CH3COOH. This change requires a student to think more critically about the nature of these solutions to answer the subsequent questions correctly. More discrimination is required to differentiate acetic acid from NaF and from MgCl2 solution behavior. Modification 2. If the stoppers were removed from the flasks, from which flask would the solute escape most readily? Explain the answer. Modification 3. The contents of which flask(s) could be used as reactant(s) in an esterification reaction? Explain. This would become a more challenging question if varying concentrations of the compounds in water were used. This change would make the question quantitative and more difficult. The quantitative nature of question 7 would make it less appropriate as a companion for question 8. These two questions should be of like nature and degree of difficulty. To avoid the quantitative aspect of concentration calculation, it would be appropriate to ask the student to identify the type of substance for each question and to write a dissociation, ionization, hydration equation (as necessary) for these substances in water and discuss their relative activity. These three items are examples of particulate representations linked to symbolic representations or macroscopic phenomena. Such questions are not part of the AP or IB examinations. 1. Which particulate representation corresponds to the equation? 2 SO2 + O2 → 2 SO3
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools 2. Which would best represent a mixture of the gases helium and chlorine? 3. If the contents of these two beakers are poured into a third beaker, what will the resulting mixture look like? This is an example of an error analysis-type item. 4. A student titrated 10.00 mL of fruit juice with 12.84 mL of 9.580 × 10–2 M NaOH. Which step is NOT correct in this calculation of mass of citric acid in 1.00 mL of juice? C3H5O(COOH)3 + 3 NaOH → Na3(C3H5O(COO)3 + 3 H2O Moles NaOH = (12.84 mL) (9.580 × 10–2 mol/L). Moles citric acid = (1.230 mol NaOH) (1 mol citric acid/3 mol NaOH). Mass citric acid in sample = (0.4100 mol citric acid) (192.12 g/mol citric acid). Mass citric acid in 1 mL fruit juice = (78.77 g citric acid)/(10.00 mL fruit juice). All the steps are correct.
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools This is an example of a laboratory-related item. 5. Consider a laboratory exercise in which you prepare approximately 200 mL of a pH = 4.35 buffer. The chemicals available for your use are: 1M solutions of acetic acid, ammonium acetate, ammonium chloride, aqueous ammonia, hydrochloric acid, sodium acetate, and sodium hydroxide (acetic acid Ka = 1.8 × 10–5 and ammonia Kb = 1.8 × 10–5). Which chemicals will you use to make your buffer? Explain your choice; use chemical equations where appropriate. How much of each chemical will you need? Show calculations to support your answer. Outline the procedure you will follow to make your buffer. Include specific equipment and glassware you will use. How will you prove that you successfully prepared the buffer? ADDITIONAL SUGGESTIONS FOR SECTION II, PART B The following are some other suggestions for Section II, Part B that are not specifically tied to the 1999 version of the examination. A 0.2 M sulfuric acid is added to a 0.2 M solution of barium nitrate. Describe what happens and write an equation representing the reaction. A small piece of solid potassium is added to 500 mL of water in a beaker. The potassium fizzes, dances about, and bursts into flame. Write an equation representing the reaction. A drop of phenolphthalein solution is added to the resulting solution. What would you observe? Explain. The panel also suggests that a useful addition would require students to identify reactions as examples of one or more of the following types of reactions: acid/base, oxidation/reduction, decomposition, combination, precipitation, gas evolution, double displacement, electron transfer, and proton transfer. (This list could be expanded or reduced.)
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools Appendix E Research Agenda for Advanced Studies in High School Chemistry The chemistry panel identified a number of topics on which research is needed with respect to advanced studies in high school chemistry: How do students who take advanced courses in high school chemistry move through their college studies (e.g., choice of major, continued interest and enrollment in chemistry), and how well do they succeed compared with students who do not take these programs? Longitudinal data are needed to address these questions. What are the actual costs for implementing, sustaining, updating, and upgrading advanced courses in the experimental sciences? Surveys of teachers are needed to determine actual costs. Is there a difference in the academic success of students whose school districts spend more money on these programs (e.g., for staff development, materials, and modern equipment and facilities) compared with districts that spend less? How much is information technology being integrated into advanced study courses, and what are the requirements for achieving such integration? To what extent do the Advanced Placement (AP) and International Baccalaureate (IB) courses reflect current approaches to teaching and learning in introductory college courses? How much variation exists in the granting of college credit and placement in courses to students who take advanced courses in high school? What are the effects of the current ordering of prerequisite and advanced courses in science? Do advanced programs favor some kinds of students over others? What backgrounds, credentials, and professional experience characterize teachers who are involved with these programs? Do these differences translate into how well students learn and achieve in the courses?
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Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools What percentage of students who take AP chemistry take it as their first course in chemistry? How well do these students fare in the course and subsequently in college chemistry courses? What proportion of students who take AP or IB chemistry do not take the examinations? What effect does the resulting lack of information about student learning have on the quality and quality control of the AP program in individual schools and on the AP program overall? Are there advantages to having schools offer clusters of advanced study courses as opposed to isolated courses? What is the impact of not doing so (for example, in small high schools that can support only one or two advanced study courses that may not be connected with each other)? Are there “critical masses” in the number of teachers in a school who teach advanced study courses? In other words, do differences in opportunities for isolated teachers to communicate with colleagues translate into differences in learning and achievement of their students? Are there “critical masses” in the number of students who enroll in advanced study courses? Are students who enroll in such courses either individually (e.g., through distance learning courses) or in small numbers at an advantage or disadvantage relative to students who are enrolled in very large classes? What percentage of schools have prerequisites or other screening procedures for entry into advanced study courses? Do more stringent requirements for entry into such courses translate into differences in scores on the respective assessments? What kinds of physical facilities, equipment and instrumentation, and support for laboratories are available to teachers and students in advanced study programs in the experimental sciences? Do differences in the level and availability of such resources have an impact on student learning and performance? Are there differences in student performance on advanced study examinations in districts or states that provide incentives to students to do well as compared with students in districts or states that do not offer these kinds of incentives?
Representative terms from entire chapter: