El Crisol Volumen 002 abril a junio 2014

EL CRISOL REVISTA CIENTÍFICA Edición 5TA. VOLUMEN 002/abr–jun 2014

COLEGIO DE QUÍMICOS DE PUERTO RICO JUNTA DE GOBIERNO 2013-2014 Comité Ejecutivo Dr. Carlos R. Ruíz Martínez, Presidente Lcda. Rebeca Soler Rodríguez, Presidente Electo Lcda. Flor R. Mattos de Jesús, Secretaria Dr. Roberto Aguayo Rosario, Tesorero Lcda. Victoria Martínez, Pasada Presidenta Delegados: Dra. Agnes Costa, Academia I Dr. Carlos Nieves, Academia II Lcdo. Eduardo Nicolau, Academia III Vacante , Gobierno I Lcda. Aida T. Fuertes, Gobierno II Lcdo. Rafael A. Ortíz, Sector Privado Lcdo. Olvin A. Ortiz, Industrial Norte Vacante , Industrial Noroeste Vacante , Industrial Oeste Josselyn A. Colón , Industrial Sur Lcda. Solmarie Borrero Mejías, Industrial Metro Lcda. Sheila Pinto, Industrial Este

Colegio de Químicos de Puerto Rico 52 Calle Hatillo Hato Rey, Puerto Rico 00919

Contenido Mensaje del Presidente 2013-2014 ................................................................................................................................... 2 Editorial ............................................................................................................................................................................ 3 What Does a Student Know Who Earns a Top Score on the Advanced Placement Chemistry Exam? ............................... 4 Cost of Petroleum vs. Natural Gas: Is Natural Gas Conversion of our Power Plants Practical? ........................................ 18 Restauración del Mural “La Plena” (Parte 2) ................................................................................................................... 23 Los artículos que aparecen en las revistas del CQPR son responsabilidad de sus autores, por lo tanto, el CQPR, la Junta de Gobierno ni sus auspiciadores se hacen responsables de las opiniones o errores que puedan contener dichos artículos.

Nuestros lectores pueden remitir sus comentarios o sugerencias por correo electrónico a jqcqpr1941@outlook.com, cqpr@cqpr1941.org o correo postal del CQPR.

Mensaje del Presidente 2013-2014 Dr. Carlos R. Ruiz Martínez, Presidente 2013-2014 CQPR ¡Saludos Cordiales Colega!

El Colegio de Químicos de Puerto Rico está listo para recibirte en su 73ra Convención Anual y Exposición PRChem 2014, a celebrarse en el Centro de Convenciones del Hotel Ritz Carlton en Isla Verde. Este año te estaremos ofreciendo 38 cursos en las áreas de forense, regulatorio, ambiental, biotecnología y farmacéutica. En las temáticas, tendremos conferenciantes que cubrirán el amplio espectro de la química, desde el café y las cervezas hasta espectroscopía Raman y Cristalografía de Rayos X. También, hemos organizado dos simposios especializados: uno en alimentos y otro en cristalografía. En estos simposios tendremos la participación de plenarios y conferenciantes de reconocimiento a nivel nacional e internacional. En este año, nuestros exhibidores se han convertido en coordinadores activos de las exposiciones para brindarte su ofrecimiento científico-técnico dentro de una actividad socio-profesional auspiciada por ellos.

El equipo de trabajo coordinado de una manera extraordinaria por la Sra. Sheila Agosto, Coordinadora de Educación Continua del CQPR, nos ha organizado un programa técnico que esperamos que sea de tu agrado y satisfaga en gran manera tus necesidades profesionales. Este esfuerzo queda evidenciado con los siguientes datos sobre el programa: el 84% de los cursos en el programa de cursos y simposios son de nuevo ofrecimiento; del total de 16.4 unidades de educación continua tenemos un 58% en mejoramiento profesional (MP) y un 42% en Química Analítica (QA).

Queremos distinguir y reconocer que los logros de estos ofrecimientos recaen en gran manera en la excelente labor realizada por la Lcda. Adnalia Flores, Presidenta del Comité de Educación Continua, apoyada por su comité. Además, reconocemos las significativas contribuciones de la Lcda. Idarmis Rodríguez, Presidenta del Comité Ad-Hoc del Programa Técnico y a la Lcda. Flor R. Mattos, nuestra secretaria de la Junta de Gobierno del CQPR. En la organización del Simposio de Alimentos agradecemos a sus organizadores la Lcda. María de Lourdes Rivera y el Dr. Ángel Custodio y los organizadores del Simposio de Cristalografía: el Dr. Jorge Colón, Dr. José A. Prieto, Dr. Edgard Resto y Dr. Juan López Garriga. Distinguimos y agradecemos al Dr. Carlos Olivo, Presidente de la ACS Capítulo de Puerto Rico, por su contribución en la organización de varios cursos en el área de ambiental.

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Editorial

Junta Editora de la Revista El Crisol 2013- 2014 Carlos Velez Luz Silva Rebecca Soler

Presidente Secretaria Vocal

Queremos que la revista electrónica ayude a mejorar tus conocimientos y que puedas compartir tus experiencias con nuestra matrícula. Está en nuestras metas que las revistas sirvan también de apoyo al Programa de Educación Continua para que los artículos que presenten o se lean puedan contar como créditos en mejoramiento profesional o analítica. Queremos felicitar a nuestra colega y ahora Dra. Luz Silva por su presentación de disertación de tesis y graduación al grado doctoral en toxicología.

En este trienio investigamos porque algunos alumnos salen bien en las pruebas de química , continuamos aprendiendo como se restauran las obras de arte y atendemos asuntos ambientales de gran interés.

¡SE PARTE DE TU REVISTA EL CRISOL!

ENVÍANOS TUS COMENTARIOS, ANUNCIOS Y ARTÍCULOS RELACIONADO A LA QUÍMICA POR CORREO ELECTRÓNICO cqpr@cqpr1941.org

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What Does a Student Know Who Earns a Top Score on the Advanced Placement Chemistry Exam?

Jennifer Claesgens,*,† Paul L. Daubenmire,‡ Kathleen M. Scalise,§ Scott Balicki,∥ Perman Gochyyev,⊥and Angelica M. Stacy# †Center for Science Teaching and Learning, Northern Arizona University, Flagstaff, Arizona 86011, United States ‡Graduate Group in Science and Math Education (SESAME), University of California at Berkeley, Berkeley, California 94720,United States §College of Education, University of Oregon, Eugene, Oregon 97403, United States ∥Science Department, Boston Latin School, Boston, Massachusetts 02155, United States ⊥Policy, Organization, Measurement, and Evaluation (POME), University of California at Berkeley, Berkeley, California 94720,United States #Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, United States Journal of Chemical Education Article ASAP ABSTRACT: This paper compares the performance of students at a high-performing U.S. public school (n=64) on the advanced placement (AP) chemistry exam to their performance on the ChemQuery assessment system. The AP chemistry exam was chosen because, as the National Research Council acknowledges, it is the “perceived standard of excellence and school quality”. In contrast to the nationally recognized AP chemistry exam, the ChemQuery assessment system is a research tool that uses itemresponse theory to map student progress on a scale of conceptual understanding in chemistry. Our findings indicate that the two types of assessments, traditional problem-solving skills and conceptual understanding, are highly correlated as measured here. However, student performance on the ChemQuery assessment is disappointingly low. On the basis of the data analysis, this paper discusses the implications of the findings with a focus on the current efforts to redesign the AP chemistry exam.

■ INTRODUCTION The goal of this research is to better understand how students learn chemistry by comparing student scores on the advanced placement (AP) chemistry exam to student scores on a measure of their conceptual understanding using the ChemQuery assessment system. To begin, a reasonable expectation for students who earn a top score of 5 on the AP chemistry exam is that they would be able to answer correctly the two limiting reactant questions in Box 1.

On the basis of the AP exam statistics, probably less than 50% of the students taking the AP exam would get full credit for their answers to the question posed in Box 1.1 In comparison, students’ responses to the ChemQuery question typically respond to the question about mole number correctly, but many are not able to answer the corresponding question on the number of molecules correctly. These results are consistent with the literature on problem-solving versus conceptual understanding in both chemistry and physics, which acknowledges that students can problem solve but maintain misconceptions that limit their conceptual understanding. 2−5 The AP test in chemistry was chosen for the comparison to ChemQuery because it is an accepted standard to qualify students to earn credit for first-year, college-level chemistry coursework.6 The value of AP exams is exemplified by the fact that students often earn extra points toward their grade point average by taking AP courses, and high schools are often measured by how many AP courses they offer to students.6 At the college level, the AP exam scores are used for Edición 5ta / Volumen 002

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Box 1. Limiting Reactant Sample Questions AP Chemistry Exam (College Board AP Program1) A 0.150 g sample of lead(II) nitrate is added to 125 mL of 0.100 M sodium iodide solution.

Assume no change in volume of the solution.

Pb(NO3)2(s) + 2NaNO3(aq)

2NaI(aq)

→

PbI2(s)

+

(a) Calculate the number of moles of each reactant. (b) Identify the limiting reactant. Show calculations to support your identification.

ChemQuery Lythcott2)

Item

88

(Adapted

from

Hydrogen and oxygen react to form water vapor in thefollowing reaction. Assume the reaction goes to completion.

credit and placement, so an assumption of the exam is that students who do well meet the typical expectations for students who take an introductory college chemistry course. In comparison, ChemQuery is an assessment system that uses a framework of the key ideas in the discipline and criterionreferenced analysis using item-response theory (IRT) to map student progress. The ChemQuery assessment system is designed to measure how student conceptual understanding develops primarily by asking for explanations to chemistry questions.7 This is in contrast to the goals of the AP chemistry test, which emphasizes problem solving to demonstrate that students have mastered chemistry topics equivalent to college coursework.

This paper begins by describing the two types of assessments.

The data analysis then compares students’ scores on the ChemQuery assessment system to 2H2(g) + O2(g) → 2H2O(g) their self-reported AP chemistry exam scores to answer the question: Does student conceptual (a) If you mix 2 moles of hydrogen and 2 understanding of chemistry measured using the moles of oxygen, how many moles of water ChemQuery assessment system correlate to vapor are produced? students’ scores on the AP chemistry test, and if so, what does this mean in terms of interpreting of student understanding of chemistry based on an AP score?

■ STRUCTURE OF THE ASSESSMENTS The AP chemistry exam and the ChemQuery assessment system are two quite distinct tests to measure student ability in chemistry. The AP chemistry exam is a large-scale examination to measure students’ knowledge of college-level general chemistry topics, while the ChemQuery assessment system is designed to measure how students’ conceptual understanding of chemistry develops over the course of instruction. Both serve different purposes but are designed to measure what students “know” about chemistry. There are two main differences in the assessment design between the exams: the first is the choice of question type and the second is how students’ responses are scored and interpreted.

The goal of the AP chemistry exam is to “prepare students to attain a depth of understanding of fundamentals and reasonable competence in dealing with chemical problems”.1 A secondary goal is to “contribute to the development of the students’ abilities to think clearly and to express their ideas orally and in writing”.1 The AP chemistry exam is designed to measure and compare students’ knowledge of a broad range of topics that include, among many others: stoichiometry; gas laws; oxidation−reduction reactions; equilibrium; and thermodynamics. Topics are distributed randomly in the exam and student understanding is measured as a total score; these scores are then norm-referenced. The AP chemistry exam consists of three sections administered over 3 h. The first half of the exam is made up of 75 multiple choice items covering Edición 5ta / Volumen 002

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a variety of topics to be answered in 90 min. The second section begins with two open-ended, free response questions to be answered in 40 min. In the final component, students choose five from among eight prompts to “translate” from written text into chemical equations within 50 min.

As a large-scale test, over half of the exam consists of answering multiple-choice items.

Students, or schools districts on their behalf, pay a fee to take the exam. Postsecondary institutions often reward high performance on the exam by awarding course credit or class waivers for first-year-level chemistry courses.8 The ChemQuery assessment system consists of a set of free response conceptual questions that are selected and administered as a high school test in a 50-min period by the students’ instructor. While the AP chemistry exam covers a broad range of topics and compares student performance based off of raw scores that are summed up across the exam, the ChemQuery assessment system uses a framework of the key ideas in the discipline and criterion-referenced analysis with item response theory to map student progress, which will be described in the next section. This exam is not high-stakes and has been used solely for research.7, 9−11 In this study, a subset of the ChemQuery assessment items were administered during class time as tests twice during the school year, once as a pretest and once as a posttest to measure student learning. Only ChemQuery posttest scores were used in the analysis to compare with students’ AP chemistry exam scores. The ChemQuery Development of the ChemQuery assessment system has used both qualitative and quantitative methods, including a grounded theory approach,12 to see what types of student thinking emerged that could then be described and measured statistically using Rasch modeling.13 An initial step entailed developing a model to organize the overarching ideas of the discipline of chemistry into a framework that is described as the Perspectives of Chemists.7 The Perspectives is a multidimensional construct map, which describes a hierarchy of conceptual understanding of chemistry ranging from novice to graduate levels along three sets of progress variables: Matter, Change and Energy. We consider these “big ideas” as the variables to measure students’ emerging understanding in chemistry within the assessment system. The Matter variable can be described as the properties associated with “stuff”, while the Change variable focuses on accounting for making “new stuff”. Energy is still in development, but the concept seems to develop from early ideas of temperature on the pathway to enthalpy and entropy. To then measure how student understanding develops along each variable necessitated thinking about how domain knowledge is organized in students’ heads, so within each variable is a scale to describe a proposed progression of how students learn chemistry over the course of instruction. The levels within the proposed variables are constructed such that students give more complex and sophisticated responses as they develop from describing their initial ideas in Level 1 (Notions), to relating the language of chemists to their view of the world in Level 2 (Recognition), to formulating connections between several ideas in Level 3 (Formulation), and eventually reaching Level 4 (Construction).

The resulting Perspectives framework is intended to describe and measure how students learn and reason using models of chemistry to predict and explain phenomena, as summarized in Table 1. The horizontal axis of the table relates the three dimensions of domain knowledge in chemistry referred to as the progress variables: Matter, Change, and Energy.

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a

The proposed Energy variable is still under development and not as well articulated at this time.

The perceived progression of explanatory reasoning that develops as students gain understanding in chemistry is along the vertical axis as Notions, Recognition, Formulation, and Construction with more sophisticated levels of understanding at the top. The purpose of the Perspectives framework is to make explicit the relationship between domain knowledge and how students make meaning of the ideas as they learn chemistry over the course of instruction.

Like learning progressions, the variables of the Perspectives framework represent an instantiation both of understanding the “big” or enduring ideas of a discipline of science14 and a tracing out and expanding on such “key ideas” to describe how students grasp increasing levels of complexity over time for core concepts.15 The pathway of understanding that is emerging from research using the ChemQuery assessment system starts with students’ Notions, which includes their everyday experiences and values their logical reasoning. The next step is Recognition. At this level students are using normative definitions, terms, symbols, and algorithms in their explanations at a unirelational level; that is, they have a simple idea for a single evolving chemistry concept. The next step in students’ understanding is Formulation: at this level, students can reason and integrate multiple ideas, concepts, or topics in chemistry. Construction is hypothetical. We have not gathered enough data to confirm our conjecture at this time. Nevertheless, the design has implications for both how students’ responses are scored and how the scores can be interpreted. The Perspectives framework is then coupled with construct-referenced IRT analysis to map student progress.

ChemQuery: Measuring Student Understanding With the use of the Perspectives framework, patterns in student responses are analyzed with item-response theory Rasch psychometric models. Item-response models are statistical models that express the probability of an occurrence, such as the correct response on an assessment question or task, in terms of estimates of a person’s ability and the difficulty of the question or task. Specifically, the scores for a set of student responses and the questions are calibrated relative to one another on the same scale (a “logit” or log of the odds scale) and their fit, validity, and reliability estimated.13 These scores are matched against the ChemQuery Perspectives framework describing levels of success in chemistry along each variable from novice student up through the expert. A key aspect of this type of assessment is the location of the question difficulty and student ability to correctly answer the question item.

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ChemQuery items 3, 6, and 10 are included as examples with the steps associated with student scores as examples. Students’ responses measuring between −1 and −0.25 fall in the Notions Level, scores between −0.25 and 1.5 are in Recognition, and scores above 1.5 measure in Formulation in the ChemQuery assessment system. These cut scores were determined by looking at the item locations and associated student scores (steps).

ChemQuery: Describing Student Understanding For this study we focused on the two variables, Matter and Change. The Matter variable, items, scoring rubrics, and analysis are described in a previous publication.7 Example of Change items and scoring rubrics including exemplars of student understanding are described here.

In ChemQuery Level I Notions, we find that students can articulate their ideas about change and matter; they use prior experiences, observations, logical reasoning, and knowledge to provide evidence for their ideas that stuff happens. For example, students responding to a limiting reactant question (Item 6) often respond with logical reasoning that the substances “cancel out” or with ideas of stuff happens with responses such as “when you combine...you make something new.” This type of Notions-level thinking is also illustrated in ChemQuery Item 3, in which students use their experience that solids are heavier than liquids; for Item 10, many students list all of the ingredients either by name or symbol (Table 2). The student responses at this level focus largely on macroscopic descriptions of change or will use information from the question to construct a reasonable response. It seems that students measuring at Level 1 Notions rarely hold models that include ideas of conservation at the particulate level and stay more focused at the macroscopic level.

In comparison, students scoring in Level II Recognition begin to explore the language (terms and concepts) and specific symbols used by chemists to describe change more fluently with early ideas of conservation. Specifically in Item 3 students correctly apply the term “conservation of mass” to explain that the mass does not change when two solutions are mixed, Edición 5ta / Volumen 002

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and in Item 10 students correctly combine ions into the associated solutions. ChemQuery Items 3 and 10 do not measure beyond Level II Recognition. However, for items that do, student responses at Level II Recognition include accurate definitions, although students’ understanding is not fully developed so that student reasoning often is limited to causal instead of explanatory mechanisms. Student responses can be correct and incomplete with limited understanding of chemistry in Level II Recognition. For example, for Item 6 on limiting reactants, students at Level II Recognition correctly recognize limiting reactants and can interpret a chemical equation but are not making the link of moles to molecules at the particulate level. Overall, at Level II Recognition, student responses tend to focus on one correct link of understanding without consideration or understanding of the other links necessary for a more robust model of explanation to the question posed. Formulation is the next level as described in the ChemQuery assessment system. At this level we are observing students correctly linking conceptual and quantitative, and macroscopic with a particulate model of understanding. Specifically, in Item 6, students are making the link between symbols, grams, and moles. Additionally, these levels are meant to be cumulative; a student cannot reach Level III Formulation without moving through Levels II and I. Comparing the Assessments Overall, the AP exam and ChemQuery have different formats, different item questions, and different statistical measures, but both the AP exam and ChemQuery are designed to measure what students know about a common set of ideas in chemistry. Yet, each exam design has implications for both how students’ responses are scored and how the scores can be interpreted. This research determines how the two exams correlate, and what each tells us about what students “know”. The AP exam is norm-referenced with a focus on problem solving skills, meaning that the scales are aligned most directly to what a range of students achieve in high school chemistry rather than to actual concepts of college chemistry. Student scores on the AP chemistry exam are summed then normally distributed. From there the scores are divided into five groups with approximately 15−20% of the students in each group, as shown in Table 3.

In 2006 when the scores were collected for the study comparison, 6150 schools offered the AP chemistry exam to a total of 78,453 students, 54% male, 45% female. (On a side note, nearly one-quarter of students are awarded a score of 1.) Overall, the AP score is determined by how students’ scores compare to each other, for a norm-referenced sample, with psychometric measures of the items based on how scores were distributed the last three years, and how well college students do on the item questions.

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In contrast, the resulting IRT analysis using the Perspectives construct tracks student learning by making people-to discipline measurements that assess links between student understanding and chemistry domain concepts, rather than the people−to−people comparisons, which is common with norm reference tests. In other words, students are placed on a scale of understanding of chemistry along each variable rather than focusing on referencing how they did in comparison to other students who took the exam.

■ STUDY DESIGN This study compared the scores of 64 students on the ChemQuery assessment to their AP chemistry exam scores. All of the students in this study were enrolled in an AP chemistry class taught by the same instructor at a public high school in the northeast. The participating students had completed one year of high school chemistry previously. Sixteen ChemQuery items were selected from the Matter and Change item pool for the ChemQuery assessment. The item parameters were previously calibrated from thousands of high school and college chemistry from previous studies, so only a subset of items were necessary to determine student ability levels in this study. A ChemQuery pretest was administered in the fall of 2005 between the first and second year of chemistry instruction, with the posttest administered in the spring of 2006 immediately following the advanced placement exam. The ChemQuery assessment was administered as an ungraded quiz to highly motivated students. All students completed the quiz during the class period. Student posttest scores on the ChemQuery assessment were compared to self-reported AP chemistry scores.

Overall, the students in this study performed better than average on the AP chemistry exam with 25%, 20%, and 23% of students scoring 3, 4, and 5 on the exam (Table 4), respectively, compared to the 2006 national averages reported by the College Board as 15%, 18%, and 23%, respectively (Table 3).

Note that only 9% of students scored a 1, which is below the national average of 25%.1 These high scores are to be expected from the sample selection of the students, who were considered highly motivated by the teacher and who attended a high school that is recognized as a highachieving school. To determine students’ score on ChemQuery, scoring rubrics with exemplars for each item question were used. Scoring involved assigning a raw score for each item a student answered based on the item exemplars, which resemble the examples from Table 2 with scores of 0−8 assigned for the various levels and sublevels (steps). Student scores were then compiled to produce a raw score for each student, with higher raw scores indicating that a

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student is at the higher levels of the construct and lower raw scores indicating that a student is at the lower level of the construct.

With the use of ACER Conquest 3.0 software, a Wright map of student posttest scores was generated (Figure 1). Inter-rater reliability was determined using Krippendorff’s α coefficient.

Responses from 10−14 students on 15 of the items were scored by all of the 7 raters, with responses from 10 students on one item (item 88a) scored by 6 raters. Krippendorff’s α coefficient provides the summary of agreement among two or more independent raters on polytomous items.16

Figure 1. Wright map and ChemQuery item difficulty levels with generalized-item thresholds.

The value of unity indicates perfect inter-rater reliability and the value of zero indicates the lack of reliability. The average Krippendorff’s α value over the entire set of items was estimated to be 0.64. The relationship between student AP scores and their scores on the ChemQuery assessment system was found to have a Pearson correlation of 0.67, with p < 0.01 on a twotailed significance test.

This indicates a clear relationship between students’ self-reported AP exam scores and their measured ability level scores using the ChemQuery assessment system (Figure 2). In other words, students scoring high on the ChemQuery exam also scored high on the AP exam, for this sample. Therefore, in this study, conceptual understanding as measured by the ChemQuery exam is correlated to the problem-solving skills measured by the AP chemistry exam. We can now discuss the correlation between the conceptual understanding that develops from Notions to Recognition in the ChemQuery assessment system linked to more traditional measures, such as the AP chemistry exam. This study shows that the two measures are correlated but that they are quite different interpretations of students’ ability or understanding of chemistry. A significant finding of this study shows that students who are passing the AP exam with scores of 3, 4, and Edición 5ta / Volumen 002

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5 are all falling in Level II Recognition as described In the Perspectives of Chemists on the ChemQuery exam, which allows us to discuss what the AP score means in terms of their conceptual understanding of chemistry.

Figure 2. ChemQuery ability levels versus AP scores.

■ ANALYSIS It is reasonable to assume that students scoring a 5 on the AP exam could correctly answer the Item 88 ChemQuery limiting reactant problem posed in the introduction (Box 1). However, this is not necessarily the case in light of the statistical analysis. The correlation between the exams indicates that students who received a score of 3 or above on the AP exam tend to answer the conceptual questions such as ChemQuery Item 88 in the Level II Recognition on the Perspectives framework. The benefit of using criterion-referenced measurement in the ChemQuery assessment system compared to norm-referenced measurement of the AP chemistry exam is that it allows one to match scores from a large-scale assessment to a construct of student understanding. In this case, we can provide a general description of the types of answers we have from students at different levels of understanding across two different assessments. Specifically here, we can describe the conceptual understanding of students who received a score of 5 on the AP chemistry exam.

For example, ChemQuery Item 88 regarding the combustion reaction of hydrogen and oxygen is an example that reaches to Level III Formulation. Students at Level II Recognition correctly answer, “How many moles of water vapor are produced?” but are unlikely to correctly answer, “How many molecules of water vapor are produced?” Using the Wright map output, students in Recognition have only a 50% probability of answering the follow up question on molecules correctly. Student responses tend to focus on one correct link of understanding without consideration or understanding of the other links necessary for a more robust model of explanation to the question posed. In other words, student answers on the ChemQuery exam typically responded correctly to the question about mole number, but statistically most students in this study were not able to answer the corresponding question on the number of molecules correctly. Measures of student understanding using the ChemQuery assessment system indicate a limited understanding of chemistry by not fully connecting terms, symbols, and algorithms to achieve a more sophisticated and intellectually flexible model of understanding.

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The link between the macroscopic, symbolic, and submicroscopic (particulate) as described by Johnstone seems to explain the difficulties we are observing in the data as students are developing their understanding toward Formulation.17 Specifically, item 88 supports Lythcott’s research that describes the disconnect between students’ problem solving and conceptual understanding.2 Overall our results are consistent with the literature on problem solving versus conceptual understanding in both chemistry and physics, which acknowledges that students can problem solve but maintain misconceptions that limit their conceptual understanding.2−5 Therefore, it is not surprising then that the high-scoring AP students are not answering the correlating conceptual ChemQuery question correctly. Yet, are these measures of understanding equivalent to a first-semester college-level chemistry course? The AP exam is validated by comparing student knowledge of high school examinees with that of students in introductory level college chemistry courses.6 Our evidence to date using the ChemQuery assessment system shows that students typically enter high school chemistry in the lower areas of Level 1 Notions. After one year of college-level chemistry, students in our data sets are in the upper region of Level II and lower region of Level III, between Recognition and Formulation. The sample group consisted of 973 students in their first postsecondary course in general chemistry at a single university.19 Percentage distribution of student scores on the Perspectives framework over the course of instruction are shown in Figure 3. Note that within each Perspective level, there are 3 sublevels of −1, 1, and 1+ in Level I Notions, for example.

Figure 3. Distribution of general chemistry college students on Perspectives in first-year chemistry.

Additionally, it should be recognized that scores on many of the ChemQuery questions can range to a much higher level on the Perspectives framework with such results achievable by at least some university-level general chemistry students, as has been demonstrated independently by first-year college students in this study.18 So even though we chose some of the easier items for illustrative purposes in the Perspectives description for this paper, it was the high school students’ ability, or understanding, of chemistry that was limiting their scores.

■ IMPLICATIONS FOR ASSESSMENT This analysis sheds some light on the level of conceptual understanding of high-scoring students on the AP chemistry exam and raises a call for uniting conceptual and problem solving to develop deep understanding and complex reasoning. Specifically, this study finds that Edición 5ta / Volumen 002

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problem solving need to look at student learning more coherently by integrating what is known about how students learn with the organization of the domain of chemistry. There is a large body of research that describes how students learn, but it has limited application to chemistry and does not seem well incorporated into chemistry assessments such as the AP chemistry exam as described here.20−22 Additionally, much of the research on student learning has been deconstructed into various knowledge types such as problem solving, conceptual change, transfer, representations, and reasoning, rather than looking at the integration of knowledge such that conceptual reasoning informs problem solving and can be measured with students.23 Talanquer speaks to these dichotomies and describes10 in chemistry education, including: “misconceptions versus scientific conceptions”, “submicroscopic versus symbolic”, and “algorithmic versus conceptual”.24 Research in chemistry education not only falls into these distinct categories but tends to be topic-specific to the domain of chemistry, such as describing student understanding of the mole,25−28 thermodynamics,29−31 or chemical change, for example.32−34 Our concern is that when the research looks at just one knowledge type or one specific topic, an overall understanding of how students learn chemistry is missing, which is where we seem to find ourselves today in chemistry education. Yet as stated in the NRC Report, the primary goal of advanced study in any discipline should be for students to achieve a deep conceptual understanding of the discipline’s content and unifying concepts,6 which seems to imply thinking more deeply about what the big ideas or unifying concepts are. The current hypothesis in science education is that organizing subject domains such as chemistry around “big ideas” will improve student learning.15, 35 In the AP chemistry redesign, six “Big Ideas” have been described: 36 1. Structure of matter 2. Bonding and intermolecular forces 3. Chemical reactions 4. Kinetics 5. Thermodynamics 6. Chemical equilibrium In ChemQuery we have posited three big ideas at the high school level: Matter, Change, and Energy. Talanquer has a different approach that emphasizes chemistry as an applied science organized around these essential questions: What is it? (analysis); How do I make it? (synthesis); How do I change it? (transformation); and How do I explain it? (modeling).37 Depending on how one interprets the science framework and Next Generation Science Standards, there can be two−four “big ideas” in chemistry. From physical science core ideas there is PS 1, Matter and its implications; PS 3, Energy; and possibly PS 2, Motion and Stability: Forces and interactions with matter and energy these are crosscutting concepts that are to be taught from K−12 and across the disciplinary core ideas.15,35 However, this is all hypothetical.

No one really knows whether the “big ideas” will help students develop explanatory power, or which “big ideas” are the most fruitful; however, the movement to integrate and unify ideas has gained momentum in K−12 science education and may prove fruitful to help bridge the gap between problem solving and conceptual understanding. One challenge then is to create good questions that capture the void between problem solving and the correlated conceptual understanding of the unifying concepts to better measure how student understanding of chemistry develops. One suggestion from our research would be to use simple numbers such as ChemQuery Item 6 and Item 88 that emphasize conceptual understanding of chemistry with simple mathematical reasoning. Another suggestion is to measure and value the development of correct explanations found in student responses to chemistry problems, which may include scoring answers beyond right or wrong to value incorrect answers that are shown to lead to deeper understanding over the course of instruction. For example, student responses in Level II Edición 5ta / Volumen 002

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Recognition contain correct chemistry that may not be fully developed to produce a right answer.

Additionally, if unifying or big ideas are proposed to be useful, then assessment questions within an organizing framework like the Perspectives of Chemists could test whether, indeed, students are developing understanding with explanatory models of chemistry implied by each proposed organizing framework. Some of the goals as stated in the NRC report for the redesign of AP courses that are pertinent in light of this research are for students to achieve a deep conceptual understanding of the discipline’s content and unifying concepts; to use assessment to certify mastery; and to ensure that the assessments measure conceptual understanding and complex reasoning.6 Furthermore, as recognized by the NRC and the AP chemistry redesign efforts, the AP chemistry exam has wide-ranging effects on teachers, curriculum, sequencing, and students,6,19 based on the common tenet in education that “what you test is what you get”. The assumption is that assessment drives instruction, which implies that the change in the AP redesign will drive changes in instruction in order to align curriculum, instruction, and assessment to facilitate “deep learning”.

■ SUMMARY This research highlights the need to better unite conceptual and problem-solving abilities to describe student understanding. Currently, we find that traditional problem-solving questions are easier for students to answer correctly with conceptual understanding lagging a step behind, even though the conceptual questions seem easier to us in chemistry education. Specifically, conceptual understanding as measured by the ChemQuery assessment system, and scores on the AP chemistry exam are correlated yet reveal different interpretations of students’ ability or understanding of chemistry. Our data analysis finds that the level of conceptual understanding is only at Level II Recognition, even for those students scoring 5 on the AP exam, which suggests that many of even the higher-performing students are much more competent at problem solving in chemistry than they are in answering the “simpler” conceptual questions. It seems that we are measuring two distinct yet highly correlated types of understanding that will behoove us as a community to more effectively address. This is not new, but the correlation between the two types of understanding is. Deep understanding that links problem solving to conceptual understanding may develop later and may require instruction and assessments that measure and value how correct explanations to chemistry problems develop. By recognizing the power of the AP chemistry exam to drive changes to improve student understanding of chemistry, our hope is that this research can contribute to the mission of the AP chemistry exam redesign efforts with the ultimate goal of helping all students learn chemistry. Journal of Chemical

■ AUTHOR INFORMATION Corresponding Author

*E-mail: jennifer.claesgens@nau.edu.

Notes: The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS This material is based upon work supported by the U.S. National Science Foundation under Grant Nos. ESI-9730634, DUE-0125651, and 0737056 (CCLI).

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■ REFERENCES 1. College Board. Setting a Policy for AP Chemistry. http://www.collegeboard.com/prod_downloads/ipeAPC/apchempg060309_51087.pdf(accessed Spring 2006).

(Note: Because the data used in comparison was specific to the 2006 AP Exam, the access date used during research is provided. Unfortunately, the data set is no longer available on the current Web site.)

2. Lythcott, J. J. Chem. Educ. 1990, 67, 248– 252[ACS Full Text ], [CAS] 3. Bodner, G. J. Chem. Educ. 1991, 68, 385– 388 [ACS Full Text ], [CAS] 4. Hestenes, D. Phys. Teach. 1993, 30, 141– 158. [CrossRef] 5. McCloskey, M. Naïve Theories of Motion. In Mental Models; Gentner, D.; Stevens, A. L., Eds.; Erlbaum Associates: Hillsdale, NJ, 1983; pp299– 324.

6. National Research Council. Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools. Center for Education, Division of Social Sciences and Education, National Academies Press: Washington, DC, 2002.

7. Claesgens, J.; Scalise, K.; Wilson, M.; Stacy, A. Sci. Educ. 2009, 93, 56– 85 [CrossRef] 8. College Board. Learn about AP. http://www.collegeboard.com/student/testing/ap/sub_chem.html (accessed Jan 2014) .

9. Claesgens, J.; Scalise, K.; Wilson, M.; Stacy, A. Assess. Update 2008, 20, 6– 9 10. Scalise, K.; Claesgens, J.; Wilson, M.; Stacy, A. Chem. Educ. Res. Pract. 2006, 7, 170– 184 [CrossRef], [CAS] 11. Watanabe, M.; Nunes, N.; Mebane, S.; Scalise, K.; Claesgens J. Sci. Educ. 2007, 91, 683– 709 [CrossRef] 12. Strauss, A.; Corbin, J. Basics of Qualitative Research: Grounded Theory Procedures and Techniques; Sage Publications: Newbury Park, CA,1990.

13. Wilson, M. Constructing Measures: An Item Response Modeling Approach; Erlbaum: Mahwah, NJ, 2005.

14. Smith, C. L.; Wiser, M.; Anderson, C. W.; Krajcik, J.Implications of Research on Children’s Learning for Standards and Assessment: A Proposed Learning Progression for Matter and the Atomic-Molecular Theory Measurement 2006, 4, 1– 98 15. National Research Council. A Framework for K–12 Science Education: Practices, Crosscutting Concepts, and Core Ideas; National Academies Press: Washington, DC, 2011.

16. Krippendorff, K. Content Analysis: An Introduction to Its Methodology; Sage: Beverly Hills, CA, 1980.

17. Johnstone, A. J. Comp. Assisted Learn. 1991, 7, 75– 83 [CrossRef] 18. Scalise, K.; Stacy, A.; Douskey, M.; Daubenmire, P.; Lim, T.; Sinapuelas, M.; Rao, S. ChemQuery as a Formative Assessment Instructional Strategy for Chem 1. Paper presented at the 240th ACS National Meeting, Boston, MA, 2008.

19. Spencer, J.; Hnatow, J. AP Chemistry: Course and Exam Review. In Chemistry in the National Science Education Standards; Lowery-Bretz,S., Ed.; American Chemical Society: Washington, DC, 2008; pp 109– 117.

20. National Research Council. Knowing What Students Know: The Science and Design of Educational Assessment; National Academy Press:Washington, DC, 2001.

21. Bransford, J. D.; Brown, A. L.; Cocking, R. R. How People Learn: Brain, Mind, Experience, and School: Expanded Edition.; National Academy Press: Washington, DC, 1999.

22. Driver, R.; Squires, A.; Rushworth, P.; Wood-Robinson, V. Making Sense of Secondary Science: Research into Children’s Ideas; Routledge:London, 1994.

23. Glaser, R. Am. Psychol. 1984, 39, 93– 104 [CrossRef] 24. Talanquer, V. J. Chem. Educ. 2012, 89, 1340– 1344 [ACS Full Text ], [CAS] 25. Astudillo, L.; Niaz, M. J. Sci. Educ. Tech. 1996, 5, 131– 140 [CrossRef] 26. Furio, C.; Guisasola, J. Int. J. Sci. Educ. 2000, 22, 1285– 1304 [CrossRef] 27. Gabel, D.; Sherwood, R. J. Res. Sci. Teach. 1984, 21, 843– 852 [CrossRef] 28. Staver, J.; Lumpe, A. J. Res. Sci. Teach. 1995, 32, 177– 193 [CrossRef] 29. Boo, H. J. Res. Sci. Teach. 1998, 35, 569– 581 [CrossRef] 30. Greenbowe, T.; Meltzer, D. Int. J. Sci. Educ. 2003, 25, 779– 800 [CrossRef] 31. Teichert, M.; Stacy, A. J. Res. Sci. Teach. 2002, 39, 464– 496 [CrossRef] 32. Hesse, J.; Anderson, C. J. Res. Sci. Teach 1992, 29, 277– 299 [CrossRef] 33. Johnson, P. Int. J. Sci. Educ. 2002, 24, 1037– 1054 [CrossRef] 34. Yarroch, W. J. Res. Sci. Teach. 1985, 22, 449– 459 [CrossRef] 35. Achieve. Next Generation Science Standards; National Research Council: Washington, DC, 2013. http://www.nextgenscience.org/(accessed Jan 2014) .

36. College Board. AP Chemistry Course Details. https://apstudent.collegeboard.org/apcourse/ap-chemistry/course-details (accessed Jan2014) .

37. Talanquer, V.Chemistry Education: Ten Facets To Shape Us J. Chem. Educ. 2013, 90 ( 7) 832– 838 [ACS Full Text ], [CAS]

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Cost of Petroleum vs. Natural Gas: Is Natural Gas Conversion of our Power Plants Practical?

By Marvin K. Ellis Chemist / Quality Manager IDI Caribe, Inc. Tel.: (787) 853-2186

Fax: (787) 853-2187 Email: mellis@idicomposites.com Website: www.idicomposites.com

As many countries worldwide, Puerto Rico’s energy supply has depended on the combustion of petroleum distillates (Diesel, Bunker A or No. 2 Fuel Oil) or petroleum residues (Bunker C or No. 6 Fuel Oil) for many years. Even when these sources are very reliable as for the amount of energy they can release, they are among the most contaminant gases producing fuels. The amount of Sulphur, Vanadium, and Asphaltenes particles produced during the combustion of Fuel Oil has been restricted and monitored by the Environmental Protection Agency (EPA). As we know, sulphur combustion result in acid rain production, Vanadium Oxide is hazardous and Asphaltenes particles contribute to the opaque mist in the atmosphere. These fuel contaminants levels are to be monitored in power plants feed at all times and kept within fuel specification limits established by the EPA. Although PREPA has its own Laboratory, it has contracted laboratories for the chemical analysis of the fuels by the means of approved ASTM or IP methods. Each fuel transfer from a ship, barge or blending tank has to be sampled and tested by both parties for contaminants and other engineering controls such as viscosity and caloric content.

PREPA spent millions of dollars per year in the chemical testing of these fossil fuels for a long time in order to comply with federal and local emissions restrictions. Also the rates of these petroleum base fuels and their constant raise are part of the complications our Island financial situation has suffered for years and brought us to the actual degraded economic condition.

It has been debated for the past decade if we should rely in the transformation of current Fuel Oil power plants to Gas Turbine driven power plants. In fact, the combustion of Natural Gas is cleaner than the heavier particles produced by Fuel Oil burning and, in turn, transformation to Natural Gas will help environment conservation.

Natural gas is often described as the cleanest fossil fuel. It produces about 29% and 44% less carbon dioxide per joule delivered than oil and coal respectively,1 and potentially fewer pollutants than other hydrocarbon fuels.2 However, in absolute terms, it comprises a substantial percentage of human carbon emissions, and this contribution is projected to grow. According to the IPCC Fourth Assessment Report, in 2004, natural gas produced about 5.3 billion tons a year of CO2 emissions, while coal and oil produced 10.6 and 10.2 billion tons respectively. According to an updated version of the Special Report on Emissions Scenario by 2030, natural gas would be the source of 1

"Natural Gas and the Environment". Naturalgas.org Website. Retrieved 2011-02-06. From Wikipedia.

“Natural Gas”. http://en.wikipedia.org/wiki/Natural_gas . Retrieved March 17, 2014.

2 Ibid.

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11 billion tons a year, with coal and oil now 8.4 and 17.2 billion respectively because demand is increasing 1.9 percent a year. Total global emissions for 2004 were estimated at over 27,200 million tons. 3 Although Natural Gas mainly consists of Methane (CH4), it is a mixture of hydrocarbons gases which will include Ethane, Propane, Butane and Pentane.4 But, while the lifetime of atmospheric methane is relatively short when compared to carbon dioxide,5 it is more efficient at trapping heat in the atmosphere, so that a given quantity of methane has 62 times the global-warming potential of carbon dioxide over a 20-year period, 20 times over a 100-year period and 8 times over a 500-year period.

Natural gas is thus a more potent greenhouse gas than carbon dioxide due to the greater global-warming potential of methane.6,7 Natural Gas is referred as “dry” when it is almost pure or 99% or more methane CH4. It is referred as “wet” when significant amounts of other gases are present. Non hydrocarbons such as Carbon Dioxide, Hydrogen Sulphide, Nitrogen Oxides and Helium may be present.

Natural Gas does not have the high Sulphur content as liquid fuels but still has Hydrogen Sulphides (H2S) gas as a component whose emissions produce acid rain in a lesser grade. Vanadium atoms and heavy residues as Asphalthenes are not present in Natural Gas. Conversion to Natural Gas is clearly better for the environment but still we have to know or understand the cost of gas use. Another consideration is the cost of conversion of fuel oil units to natural gas. This involves changing burner tips and other equipment. Also, refrigerated storage consideration is a major factor. We can only imagine the cost of the most distinctive landmark in the shores of the Guayanilla Bay, a colossal one million barrels capacity Natural Gas reservoir tank used by Eco-Electrica Power Plant.

Hydrocarbons burn as they have Carbon, Sulphur, and releasable Hydrogen atoms available for oxidation when exposed to ignition sources. The more carbon atoms and releasable Hydrogen in the molecule of the hydrocarbon, more heating capacity this molecule can provide. Hydrogen is restricted to the amount of Oxygen available to form the more stable water molecule. We can establish that the heating value of a hydrocarbon will increase as the number of carbon atoms is present in its molecule.

3

Wikipedia. “Natural Gas”. http://en.wikipedia.org/wiki/Natural_gas . (retrieved March 17, 2014) P. Ciais, , C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C.Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 5 Andrew C. Revkin and Clifford Krauss. "Curbing Emissions by Sealing Gas Leaks". NY Times. October 14, 2009. Retrieved 11 June 2013 From Wikipedia. “Natural Gas”. http://en.wikipedia.org/wiki/Natural_gas . Retrieved March 17, 2014.

6 U.S. Environmental Protection Agency and Eastern Research Group, Inc. (ERG). “Methane and Nitrous Oxide Emissions From Natural Sources”. 2010. EPA. Retrieved March 17, 2014.

7 Khalil, M. A. K. (1999). "NON-CO2 GREENHOUSE GASES IN THE ATMOSPHERE". Annual Review of Energy and the Environment 24 (1): 645–661.doi:10.1146/annurev.energy.24.1.645. ISSN 1056-3466 4

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The burning of saturated organic molecules is represented as the oxidation of Carbon atoms in presence of an ignition source as the simple addition such as; C + O2 → CO2, which is represented for some gases below.

For Methane;

8

CH4 + 2O2 → CO2 + 2H2O + Energy (213 Kcal/mole) For Ethane; 2C2H6 + 7O2 → 4CO2 + 6H2O + Energy (For 2 molecules x 373 Kcal/mole = 746 Kcal/mole) For Propane; C3H8 + 5O2 → 3CO2 + 4H2O + Energy (531 Kcal/mole)

It is clear that amount of heat produced in combustion of an unsaturated organic compound is dependable of the number of carbons atoms in its molecule. It is easier to calculate the energy produced from pure compounds than for heavier fuels mixtures such as Diesel or heating oil. For practical purposes, we may rely on the specific sample testing results and typical heating value specifications for the latest two. As per local specifications for PREPA’s No. 6 or Bunker Fuel oil, should have at least 150,000 Gross Btu’s /Gallon heating value. Diesel must have above 18,600 Btu’s / Lb. Conversion of our power plants heavy fuels furnaces into Natural Gas turbines has been in public debate during the past decade. Politicians have broadly claim that the cost of Natural Gas is lower than the cost of bunker oil or diesel, but they has not provided actual facts and numbers of how they came to that conclusion. They now ask us to trust their 6 year plan to bring the Kilowatt hour price from 26 cents to 16 cents, but we have been asking how PREPA’s Management had come with this and previous energy prices.

Reliable and factual evidence must be explained in simple terms to the people in order to sustain any gas power plant conversion project. Government official’s consultants should have the necessary knowledge and objective rationale for giving the proper directions for our energy needs. Most people will like these questions to be answered and rely on straight forward information. How can Natural gas conversion supporters and their counterparts may persuade decision makers in favour of their respective positions depends on their knowledge of fuels potential chemical energy and the efficiency of the power generating technology used. Potential Energy from fuel or Calorific Value can be measured in Kilocalories, Mega joules, and British Thermal Units (BTU). Energy eventually can be calculated as Kilowatts hours, the most common unit everyone knows from their electric power bill. We demonstrate a simple way to compare the use of Oil vs. the use of Natural Gas, in terms of the cost of Kilowatt for both. Example below shows that the cost of energy produced by Natural Gas turbines may be five times lower than current cost by the use of oil power plants.

8

Ralph J. Fessenden & Joan S. Fessenden, Organic Chemistry 2nd Ed., Willard Grant Press, 1982. Heat of Combustion, p100.

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Colegio de Químicos de Puerto Rico EL CRISOL Revista Científica enero-marzo 2014 Formula for calculating the amount of fuel used to generate a kilowatt-hour (kWh) of electricity:9 Amount of fuel used per kWh = Heat rate (in Btu per kWh) / Fuel heat content (in Btu per physical unit)

Calculation examples using the formula and the assumptions below: Amount of fuel used to generate one kilowatt-hour (kWh): Natural gas = 0.00796 Mcf (1,000 cubic feet) Petroleum = 0.00188 barrels (or 0.08 gallons) Assumptions:

Power plant heat rate Natural gas = 8,039 Btu/kWh Petroleum = 10,991 Btu/kWh Fuel heat contents Natural gas = 1,023,000 Btu per 1,000 Cubic Feet (Mcf), this may produce 127.25 Kw. Petroleum = 5,861,814 Btu per Barrel (42 gallons) Note: Heat contents vary by type of petroleum product. This may produce 533.33 Kw. The cost of Natural Gas is 4.97 U.S. dollars per 1,000 cubic feet10 and the cost of oil is 104.82 U.S. dollars per barrel11. That brings us to the cost of KW for each one is $0.04 and $0.20, respectively.

It is important to recognize that the results may be converted to measuring units such as dollars per Kw for general discussion. It is now that we should ask lobbyists how much Natural Gas cost as dollar/ Kw against other fuels.

Other considerations are power generating company compliance with Code of Federal Regulations 40 CFR part 60.45 Emissions and Fuel Monitoring compliance which reads as follows; (a) Each owner or operator of an affected facility subject to the applicable emissions standard shall install, calibrate, maintain, and operate continuous opacity monitoring system (COMS) for measuring opacity and a continuous emissions monitoring system (CEMS) for measuring SO2 emissions, NOX emissions, and either oxygen (O2) or carbon dioxide (CO2) except as provided in paragraph (b) of this section.

Emissions from Natural Gas combustion may be low in SO2 and Nitrous Oxide. With cleaner burning low profile opacity, the operator main concern may be CO2 emissions.

CFR part 60.45 also clarifies that If an owner or operator is not required to and elects not to install any CEMS for either SO2 or NOX, a CEMS for measuring either O2 or CO2 is not required. However, the operator has to prove by scientific data the SO2 or 9

US Dept of Energy. Independent Stadistic and Analysis Website. US Energy Information Administration.

“Frequently asked Questions”. http://www.eia.gov/tools/faqs/faq.cfm?id=667&t=2. (Retrieved March 17, 2014) 10 US Dept of Energy. Independent Stadistic and Analysis Website. US Energy Information Administration.

“Natural Gas”. http://www.eia.gov/dnav/ng/hist/n3035us3m.htm . (Retrieved March 17, 2014) 11 Miguel Barrientos. IndexMundi database. Crude Oil monthly price. http://www.indexmundi.com/commodities/?commodity=crude-oil . (Retrieved March 17, 2014) Edición 5ta / Volumen 001

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NOX emissions do not exceed federal regulated levels. Local Environmental Agency (“Junta de Calidad Ambiental”) requirements and fees may apply.

We will prefer to rely in renewable power sources such as solar or wind energy power but, it is not possible at this time or the near future to have all our energy system conversion into it. Current system infrastructure, politics and business interests may not allow this to happen for a long time. In conclusion, it is time for energy production conversion supporter to demonstrate that the economic benefits of Natural Gas are factual. It is also recommended to politicians in charge to rely in the local scientific and engineering community for Natural Gas conversion evaluation and implementation.

References: Barrientos, Miguel. IndexMundi database. Crude Oil monthly price. http://www.indexmundi.com/commodities/?commodity=crude-oil . Retrieved March 17, 2014.

Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Fessenden, Ralph J & Fessenden, Joan S., Organic Chemistry 2nd Ed., Willard Grant Press, 1982. “Heat of Combustion”.

Khalil, M. A. K. (1999). "NON-CO2 GREENHOUSE GASES IN THE ATMOSPHERE". Annual Review of Energy and the Environment 24 (1): 645–661.doi:10.1146/annurev.energy.24.1.645.

Naturalgas.org Website. "Natural Gas and the Environment". Naturalgas.org Website. Retrieved 2011-0206. From Wikipedia. “Natural Gas”. http://en.wikipedia.org/wiki/Natural_gas . Retrieved March 17, 2014.

Revkin, Andrew C. and Krauss, Clifford. "Curbing Emissions by Sealing Gas Leaks". NY Times. October 14, 2009. Retrieved 11 June 2013 From Wikipedia. “Natural Gas”. http://en.wikipedia.org/wiki/Natural_gas . Retrieved March 17, 2014.

U.S. Environmental Protection Agency and Eastern Research Group, Inc. (ERG). “Methane and Nitrous Oxide Emissions From Natural Sources”. 2010. EPA. Retrieved March 17, 2014.

US Dept of Energy. Independent Stadistic and Analysis Website. US Energy Information Administration.

“Frequently asked Questions”. http://www.eia.gov/tools/faqs/faq.cfm?id=667&t=2. Retrieved March 17, 2014 US Dept of Energy. Independent Stadistic and Analysis Website. US Energy Information Administration.

“Natural Gas”. http://www.eia.gov/dnav/ng/hist/n3035us3m.htm . Retrieved March 17, 2014 Wikipedia. “Natural Gas”. http://en.wikipedia.org/wiki/Natural_gas . (retrieved March 17, 2014)

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Restauración del Mural “La Plena” (Parte 2) Por SOL E. RIVERA DELGADO Ave. De Diego #299 Santurce, PR 00910 srivera@mapr.org

Continuación del Resumen del Informe del tratamiento de restauración aplicado en el mural La Plena de Rafael Tufiño de la colección del Instituto de Cultura Puertorriqueña (ICP). Desde mayo de 2012noviembre de 2013.

Continuamos con la descripción de los trabajos de restauración de la obra “La Plena” de Rafael Tufiño.

Descripción de las técnicas de análisis realizados en el mural.

1) Análisis de Espectrofotometría Infrarroja Transformada de Fourier (FTIR) (a) Esta técnica es una herramienta muy valiosa, para determinar la naturaleza orgánica de ciertos compuestos, en especial, para discriminar entre pinturas en aceite o acrílica. Para el muestreo se utilizará una micro-jeringuilla (Harris Unicore™, 1.0 mm). El muestreo para FTIR requiere obtener una muestra, para verificar la naturaleza orgánica (caseína) en partes que no han sido intervenidas.

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(b) Las nuestra tomadas se analizaron en un FTIR, del Centro de Caracterización de Materiales (MCC, en inglés) de la Universidad de Puerto Rico. Los resultados obtenidos por FTIR sobre la muestra obtenida sobre el mural de Tufiño. (c) Muestreo de FTIR (d) Análisis de laboratorio que requiere la toma de muestra (2 horas) para verificar la naturaleza proteica de la caseína en partes que no han sido intervenidas.

2) Análisis Estratigráfico con Microscopía de Barrido de Electrones (SEM) y Espectroscopía de Energía Dispersa (EDS) (a) Técnica de espectrofotometría acoplada con un (SEM), que se utiliza para analizar la morfología o forma de la muestra, a un rango por debajo de 100 micrones. La imagen obtenida es analizada visualmente en función al (EDS), que devela la composición elemental en espectros, mediante dispersión energética de sus electrones. En conjunto, se presenta la imagen y su espectro, para el desarrollo del análisis de la composición elemental de cada uno de los estratos que componen una pintura: soporte, estrato preparatorio y capa cromática.

3) Análisis de Composición Elemental utilizando Espectrometría de Fluorescencia de Rayos X (XRF) 12 (a) La técnica de fluorescencia de Rayos X provee información sobre la composición elemental del material analizado. La muestra bajo análisis es irradiada con Rayos X, causando la expulsión de electrones de los átomos en el material. El átomo resultante constituye un estado excitado con respecto a su configuración electrónica. El relajamiento del átomo, a su estado raso (con una energía mínima), está mediado por transiciones de los electrones de niveles energéticos más altos a niveles de energías más bajas. Estas transiciones producen, a su vez, radiación con una energía determinada por la diferencia entre los niveles electrónicos envueltos. (b) Para asegurar la calidad de los datos es necesario construir un mapa de análisis, en donde se ubique la posición exacta del muestreo con XRF. Para eso se diseñó el mapa de muestreo, como se ilustra en la figura 18. 13 12 Este análisis no forma parte de los costos y contrato del profesor Lugo. Sin embargo, los análisis serán realizados y completados, bajo el acuerdo de colaboración entre el MAPR y El Departamento de Física/NASA, de la Universidad de Puerto Rico, en Río Piedras. Los análisis estarán a cargo del Dr. Antonio Martínez Collazo y del profesor Lugo.

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4) Caracterización Con esta metodología de trabajo pudimos determinar el proceso creativo del artista y de esta forma conocer a profundidad los recursos de los que se valió para crear y nos indica como pinta el artista y su evolución. Con esta metodología pudimos corroborar los objetivos números 2 y 6.

RESUMEN DE LOS RESULTADOS DE ANÁLISIS LUMÍNICOS Y QUÍMICO-FÍSICOS realizados en el mural La Plena partiendo de los objetivos esenciales planteados en la metodología científica: 1. La confirmación del medio pictórico utilizado por el artista.

Los análisis EDS, realizados en las muestras de la capa pictórica tomadas del mural, se pudo identificar los elementos de Fosforo y Calcio, los cuales son los elementos inorgánicos que componen la caseína. Los que nos indica que la pintura comercial utilizada por el artista Rafael Tufiño para pintar el mural La Plena era caseína.

2. Corroborar si la pintura comercial utilizada por el artista tenía asbesto.

Con la realización de los análisis EDS en las muestras de capa pictórica tomadas del mural se concluyó que hay presencia de Silicio (Si) en algunas de las muestra es alta la presencia de Silicato (SiO3 ˉ²). Esto puede corresponder a la presencia de asbesto en la pintura comercial utilizada por el

13 Informe final del análisis físico-químico.

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artista, la información también se corrobora con la información buscada en internet relacionada a los componentes de la pintura comercial.

3. Mostrar los posibles cambios en la composición y modificaciones realizadas por el artista durante la realización del mural.

En el caso de Rafael Tufiño sabemos por medio de los análisis lumínicos que realizó un boceto o dibujo total de las escenas, hecho que se puede constatar por medio de una fotografía tomada al artista mientras realizaba el mural.

Antes de la realización del mural el artista realizó un boceto del mural, en este se puede apreciar la idea inicial del mural en su composición.

Boceto inicial del mural La Plena

En el panel 5B (P13-RIR-IRCCD) en la imagen digital obtenida se puede observar la cuadricula realizada por el artista al transferir el dibujo, en el áreas de los pies y los adoquines.14 En el panel #6A arrepentimiento en el área del hombro de la señora llorando y en la cabeza del primer militar. En el panel #8B (la señora en el suelo) la cabeza de esta en el boceto esta inclinada para atrás en el mural esta misma señora tiene la cabeza para el lado En el panel #1B en el dibujo preparatorio en la cabeza y la mano de la mujer hay una modificación.

14

Para mayor información al respecto favor de referirse a los informes: Informe final del análisis lumínico y físico-químico del mural La Plena localizado en los anejos. Informe de tratamiento aplicado.

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4. Determinar si el artista Rafael Tufiño durante los dos años que duró la creación del mural cambio los materiales y el medio que uso.

La técnica del artista es la misma aunque parece haber cambiado de pinturas. Por los análisis realizados, encontramos algunas diferencias en los blancos (ZnO2) y (TiO2) (azules)(Prussian y Cobalto) y hay pigmento blanco de plomo. De esa forma podemos confirmar el mapa de campeo de color del mural con los resultados de XRF. 5. Conocer y documentar las alteraciones, mutilaciones si alguna que haya sufrido el mural y establecer un juicio crítico en las razones que pudieron causar deterioro y razonado los tratamientos adecuados para su restauración y posterior conservación del mural La Plena.

Se documentó fotográficamente el estado de conservación del mural de forma general e individual, los daños en la superficie de la capa pictórica, tales como: grietas, polvo, abrasiones, mutilaciones, pérdida de capa pictórica, grafitis, injertos, perforaciones. Todos los daños encontrados en los paneles en la capa pictórica y por el reverso del soporte original se localizaron en los diagramas de daños.15 El mural de documento fotográficamente y se le realizó varios exámenes con luz visible, UV e IR.16 El mural La Plena sufrió varias alteraciones en el soporte original, cortes en los bordes superior e inferior, dividieron en cuatro los panales 4 y 8. La alteración más importante realizada en el mural fueron hechas en el panel #4, el soporte fue dividido en cuatro partes y en la esquina superior derecha el soporte fue cortado nuevamente de forma oblicua, posteriormente este corte con forma de triángulo se pierde.17 Foto tomada después del 1963. El mural fue montado en la Biblioteca de Rehabilitación Vocacional de Servicios Sociales, donde el mural tuvo que ser alterado para que pudiera ser montado en la pared. Además de la pérdida de soporte en la esquina superior derecha, se puede apreciar que el panel número 8 está más oscuro que el resto del mural, se presume que se debe a una intervención anterior a la de A. Konrad en el 1985.

15

Referirse a los diagramas de daños, en los anejos.

Referirse a los informe de tratamiento de los paneles y al Informe final de análisis lumínico y físico-químico del mural La Plena.

17 Referirse al informe del panel número 4 y 8.

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Posteriormente en el área se le realiza un injerto en masonite, intervención que se presume que realizo el Sr. Anton Konrad, este hecho no está documentado en su informe. También ha injertos en el panel #8C en el borde inferior y en el panel #3B en el borde inferior. El soporte original del lado derecho del mural (en los paneles#4 y #8) es irregular y el soporte sobresale del soporte secundario (honeycomb). Todas estas alteraciones fueron realizadas para amoldar el mural a la pared donde se instalaría.

Algunos de los paneles se le realizaron macrofotografías en la capa pictórica con la Nikon ShuttlePix P-400R. En el panel #2 se documentaron varios tipos de daños:  Pérdida de capa pictórica donde se puede ver el soporte, la capa de imprimación, Esta fue tomada a una magnificación de 5x.  Grietas rectangulares finas, estas son causadas por contracción temprana ya sea por al proceso químico que se produce al secarse las capas de pinturas o a procesos mecánicos.

En el panel #8C se documentó el daño que le produjo el roce de un objeto en la capa pictórica. A principio del daño el objeto le transmitió su color en la superficie de la capa pictórica, según avanza el contacto se crea una incisión en la capa pictórica del panel.

6. Con los análisis de caracterización se expondrá la paleta de color utilizada por Tufiño en la ceración del mural, esta nos servirá para la crear una base de datos del artista y así identificar las posibles falsificaciones y poder certificar en base a la comparación de datos la autenticidad de las obras del artista.

Se tomaron muestras de capa pictórica de los colores más representativos en el mural La Plena. a) Azul Oscuro: Con los análisis realizados EDS el espectro obtenido de la composición del color que este está constituido con: Silicio; Aluminio, Sodio, Azufre. También tiene en pequeñas porciones: Titanio, Bario, Hierro, y Zinc, de acuerdo al porciento y los elementos el pigmento utilizado es azul ultramarino. b) Azul claro: Con los análisis realizados EDS el espectro obtenido de la composición del color que este está constituido con: Silicio; Aluminio, Sodio, Azufre, Calcio; Zinc corresponden a la mezcla de pigmento utilizado es azul ultramarino y blanco de Titanio.

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c) Rojo: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Cadmio, Silicio, Aluminio, Azufre y Fosforo esta composición es de rojo cadmio. d) Tierra clara tostada-amarilla: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Silicio, Aluminio, Azufre, Cadmio/Calcio, este pigmento tiene un porciento alto de Azufre y Cadmio, con trazas de hierro lo que indica que esta composición corresponde a una mezcla de amarillo de Cadmio, Tierra de Siena Natural y óxido de Hierro. e) Amarillo: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Hierro, Cadmio y trazas de Titanio, este pigmento tiene un porciento alto de Hierro y Cadmio, indica que esta composición corresponde a una mezcla de amarillo de Cadmio y Amarillo sintético y Óxido de hierro Hidratado. f) Blanco: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Silicio, Titanio, Aluminio y Zinc con trazas de Cadmio, esta composición corresponde a una mezcla blanco de Titanio y blanco de Zinc con trazas de amarillo cadmio. g) Negro hueso: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Calcio, Fosforo, Aluminio, Silicio, este pigmento tiene un porciento alto de Fosforo y Calcio, indica que esta composición corresponde a pigmento negro de calcio (hueso) y Carbono. h) Análisis comparativo de las dos secciones del panel #426.

(1) Tierra oscura: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Silicio, Bario, Azufre, Aluminio, indica que esta composición corresponde a una mezcla de Tierra ámbar + trazas de rojo de Cadmio.

(2) Tierra oscura: muestra tomada del retoque #4: Con los análisis realizados EDS el espectro obtenido de la composición elemental.

(3) tiene Aluminio, Silicio, Calcio, Hierro, indica que esta composición es diferente a la nuestra original anterior.

(4) Azul Oscuro: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Silicio, Aluminio, Calcio, Manganeso indica que esta composición corresponde a un pigmento azul ultramarino.

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(5) Azul cielo: Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Silicio, Sodio, Aluminio, Calcio, Azufre. Esta composición corresponde azul ultramarino.

(6) Rojo: (área de la llama de fuego): Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Calcio, Silicio, Aluminio, Azufre, Manganeso, Cubre indica que esta composición corresponde a una mezcla de rojo de óxido de hierro + rojo de siena puro+ óxido de hierro natural con Manganeso.

(7) Rojo (cuerno del diablo): Con los análisis realizados EDS el espectro obtenido de la composición elemental tiene Cadmio, Silicio, Aluminio, Azufre, Fosforo, indica que esta composición corresponde a un pigmento rojo cadmio.

7. Determinación de la composición elemental de los pigmentos utilizados por el artista en el mural. En este análisis de Fluorescencia de rayos x (XRF) se obtuvieron 264 muestras.

8. Comparación en el panel #4, de la composición elemental de algunas áreas de color originales, versus áreas retocadas. a) El panel 4 (P4) era el panel de investigación en esta etapa, así como la verificación de los retoques observados en varias zonas. Este panel que consiste en tres partes que fueron alteradas para adoptar el mural en su origen, posee diferencias substanciales en composición elemental, específicamente en los retoques. b) El panel izquierdo del P4, las flamas y figuras no tenían el rigor de Tufiño, sin embargo, el segmento irregular superior derecho que se guardó, fruto de la mutilación realizada mientras el mural estuvo en el Centro Vocacional, contiene pigmentos característicos y en correspondencia con el resto de los paneles con zonas originales de Tufiño. Existe la posibilidad de que alguien haya intervenido sobre esta sección, para darle continuidad estéticamente a la sección adjunta, que reconocemos tanto teórica como empíricamente como una intervención en restauración por parte de Konrad. c) Colores azules nominados como: “Dark Blue” (DBL1 y DBL 2) y los rojos, nominados como “red” (R1 y R2). Las muestras de color analizadas en la sección izquierda están compuesta por elementos (pigmento: Azul de Cobalto (P4G3DBL2), con evidentes trazas de plomo (Pb), diferente en comparación a la sección izquierda: Blue oxide (“Prussian blue”; P4DBL1C1).

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El titanio en esta muestra última sección corresponde al estrato preparatorio.

Los tonos rojos también poseen diferencias en las muestras analizadas d) La hipótesis planteada por el grupo de trabajo, significando la presencia de metales pesados en las zonas auténticas de Tufiño, son indicadores de interés de autenticidad en esta obra. Varias muestras con retoques han sido analizadas y preliminarmente, observamos las diferencias en composición elemental, y que corresponden a las áreas que la Conservacionista del MAPR, Sol E Rivera y sus colaboradores, constataron a la hora de la remoción en el proceso de restauración.

La Ejecución Práctica (Una vez realizados todos los análisis: ¿Qué hacemos?)

Evaluada toda la documentación recopilada por medio de los análisis físico-químicos, historia de la obra y su estado de conservación; se procedió a trazar el tratamiento aplicar en el mural.

Objetivos de la metodología práctica 1) Disminuir el peso de los paneles.

2) Al P#8 igualar visualización tonal con el resto del mural. 18 3) Remover el barniz con brillo de la capa pictórica de todo el mural.

4) Remover franjas de adhesivos 5) Estabilizar los paneles del mural, ya que esto han perdido adhesión y están sueltos 6) Corregir de ser posible las separaciones entre los paneles.

7) Mejorar la unión de todos los paneles del mural al soporte auxiliar ya que este deja expuesto los bordes el soporte de original.

Se procede a la contratación de técnicos de conservación Bianca M. García Martínez19 y Rene G. Sandín20 para la restauración del mural La Plena.

Debido a que el mural está expuesto en la galería MOVA del MAPR, se toma la decisión para no afectar la lectura del mural con espacios en blanco, que a medida que se remuevan los paneles de la galería para ser restaurados estos se van a sustituir con impresiones tonales de los paneles.

18 19 20

Foto de la revista Plástica.

Bachillerato en conservación y restauración de obras de artes de la Universidad de Delaware.

Maestría en conservación de pintura de la Universidad Queen en Ontario, Canadá.

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Resumen de los resultados implementados para resolver los objetivos de la metodología practica 1) Disminuir el peso de los paneles: Para cumplir con el objetivo número 1 debido que los paneles del mural tienen diferentes dimensiones se determinó pesar el panel #1 que es representativo del resto de los paneles pequeño del mural y el panel #2 el cual es representativo de los paneles de gran tamaño del mural. Se procedió a pesar los dos paneles el #1 “Cortaron a Elena” y #2 “Temporal”. El panel #1 antes de la intervención pesaba 98 lb y una vez terminada la intervención de restauración y colocado el bastidor de aluminio el panel peso 60 lb. El panel #3, antes de la intervención pesaba 123 lb y una vez terminada la intervención de restauración y colocado el bastidor de aluminio el panel peso 85 lb. Con esta disminución en el peso logramos mejorar la manipulación de los paneles durante los traslados y el sistema de enganche.

2) Para igualar visualización tonal del panel #8 con el resto del mural.21 3) Remover el barniz con brillo de la capa pictórica.

4) Remover franjas de adhesivos La ejecución de los objetivos prácticos 2, 3 y 4 están expuestos en los informes de tratamiento aplicados de todos los paneles del mural La Plena.22 En estos informes se describe el estado de conservación individual de cada panel, antes de esta intervención de restauración, la realización documentación fotográfica de los análisis lumínicos (luz visible, UV e IR) y el tratamiento de restauración aplicado y documentado fotográficamente.

Se tomó una muestra de resina del panel #6A del área de la correa para analizarlo y determinar el tipo de adhesivo aplicado, para así determinar el solvente adecuado para realizar su remoción. El análisis químico-físico realizado fue FTIR. El espectro de la muestra, al compararlo con varios tipos de resina sintética sus picos se parecen al barniz mate (Artists Matt Varnish) de Winsor & Newton.

21foto 22

de la revista Plástica

Informe Restauración mural La Plena

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Espectro de barniz mate “ Artists Matt Varnish” de la marca Wisor & Newton.

5) Estabilizar los paneles del mural ya que estos habían perdido adhesión y estaban suelto. Todos los paneles fueron removidos del soporte auxiliar, al removerlos del honeycomb se pudo apreciar que por el reverso del soporte en la intervención de restauración del 1987 le adhirieron formica para reforzar las áreas donde: habían injertos, el soporte original tenía grietas o estaba delaminado, todas estas áreas débiles, en la restauración anterior estas áreas se reforzaron con la formica. El adhesivo utilizado para adherir la formica al masonite estaba cristalizado. Todas las formicas fueron removidas del reverso del soporte original de forma mecánica, para tener una superficie uniforme en el soporte al colocar el nuevo bastidor auxiliar realizado en aluminio y Sintra.23 El estado de conservación de los paneles 3B, 4B, 5A, 6B es frágil.24

6) Corregir de ser posible las separaciones entre los paneles. En el mural, debido a las modificaciones realizadas en el soporte, los paneles no unen correctamente con los paneles circundantes creando en algunos paneles unas separaciones de ½”, 5/8” y 1 ¼”.

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Informe Restauración mural La Plena

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Ver diagramas de daños de los paneles

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Foto del montaje del mural para ver las separaciones entre los paneles. En el borde derecho del mural, los paneles 4B y 8C sobresalen dejando expuesto el soporte original del mural.

7) Mejorar la unión de todos los paneles del mural al soporte auxiliar ya que este deja expuesto los bordes el soporte de original.

Cada panel está constituido de dos partes A y B, con las excepciones de los paneles #4 y #8 que tienen respectivamente cuatro partes. A estos paneles se le realizó un bastidor de aluminio con Sintra que para corregir sus problemas de separación y de dimensiones particulares. Los bastidores se realizaran con las dimensiones mayores de los paneles para así poder corregir los problemas antes mencionados.25 El problema de las separaciones entre los paneles, se le planteó a Marilú Purcell, la Directora del Programa de Artes Plásticas de ICP, y se solicitó una reunión para buscar posibles soluciones a los problemas de unión de los paneles y la continuidad de las figuras sin que se vieran movidas, para realizar el bastidor de aluminio que iba unir los paneles.

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Para mayor información referirse al tema Diseño bastidores de aluminio

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