01:160:307 Lecture Notes - Lecture 10: Organic Chemistry, Chemical Formula, Mass Spectrometry

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7 May 2018

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CHAPTER 1

Problem Solving in Organic Chemistry

1.1 A General Approach to Problem Solving

By the time you reach Organic Chemistry, you’ve been solving homework

problems and exam problems for years. Yet it is not unusual to find students

solving Organic Chemistry problems incorrectly because of errors in their

approach to solving problems, rather than their lack of knowledge.

Almost every problem you will encounter in chemistry or other disciplines is

approached in pretty much the same way. Some aspects of the approach are almost

completely obvious, but students sometimes neglect them.

The first thing you do when you encounter a problem is size up the situation.

If it is a written problem you read it and decide what you have to do to solve it. In

order to make this decision, you must know what is being asked for and what is

being given. The next thing you do is decide how to go about doing what you have

to do to solve it, based on what is asked and what is given. Having decided what

you have to do and how to do it, you go ahead and solve the problem. Depending

on the problem, this step will require certain skills and certain facts. Finally you

look at your solution and check to make sure it makes sense and provides what the

problem asks.

Now for the details. Read the problem slowly and carefully. Determine

exactly what it is asking. Almost every problem has conditions stated or implied.

In the numerical problems that were so important in General Chemistry and that

you will also encounter, but to a lesser extent, in Organic Chemistry, the solution is

a number. You have to be sure exactly what number is being asked for, what its

units are, and how many significant figures it should have. Most of the problems

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you will encounter in Organic Chemistry are nonnumerical ones. You have to

decide exactly what is being asked for and how it should be presented.

1.2 Memorization, Understanding, Skills, and Combining Them. Types of

Problems

You have no doubt heard about all the “memorization” that you will have

to do in Organic Chemistry. But, just as you can’t learn to speak a foreign

language simply by memorizing vocabulary words; you can’t learn what

Organic Chemistry is really about by memorization alone. Understanding

is critical as well. In addition, mastery of Organic Chemistry also

requires mastery of a number of skills. Problems are designed to help you

hone those skills or to allow your instructor to assess your mastery of the

skills. So when you start thinking about how to solve a problem, consider

what skill or skills you need.

Perhaps the first and most important skill you will need to master is

drawing structures, which is a skill that you learned to a limited extent in

General Chemistry. You should be able to describe organic molecules

using Lewis structures, based on preferred numbers of bonds and formal

charges. You should also be able to draw or interpret the range of

condensed structures, including line angle drawings that are used in

organic chemistry. Drawing structures is an essential part of using the

theory of resonance. So you should be able to draw important

contributing structures for resonance hybrids to explain and predict

properties of chemical species. Finally constitutional isomerism (different

compounds with the same formula) is a fundamental topic in Organic

Chemistry and you must be able to draw constitutional isomers when

given a formula.

Many problems ask you to draw the structures of one or more compounds

that fit a certain description. Be sure the compounds whose structures you

draw fit the description. Be sure you represent the structures in the way

the problem requires. You may be asked for Lewis structures (with or

without lone pairs), condensed structures, or line angle drawings. Other

problems may give you the structure of the compound and ask for its

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Document Summary

By the time you reach organic chemistry, you"ve been solving homework problems and exam problems for years. Yet it is not unusual to find students solving organic chemistry problems incorrectly because of errors in their approach to solving problems, rather than their lack of knowledge. Almost every problem you will encounter in chemistry or other disciplines is approached in pretty much the same way. Some aspects of the approach are almost completely obvious, but students sometimes neglect them. The first thing you do when you encounter a problem is size up the situation. If it is a written problem you read it and decide what you have to do to solve it. In order to make this decision, you must know what is being asked for and what is being given. The next thing you do is decide how to go about doing what you have to do to solve it, based on what is asked and what is given.

Related Questions

please help me with this lab.

Ethanol Production

(Thermal Energy Conservation)

Lab Objective

Through this lab exercise, the principle of conservation of charge will be demonstrated using an adopted problem-solving methodology and a simple Matlab exercise.

Materials

Matlab 2007 or higher

Lab Assignment

Introduction

GASBUGS INC. is actually a division of a much larger alternate, fuel-generating corporation known as BIOFUELS INTERNATIONAL. One thing this company produces is ethanol (C₂H₆O) from an industrial process that uses a type of yeast (Saccharomyces cerevisiae). The elemental formula of S. cerevisiae is CH_1.83 O_0.56 N_0.17 and it has a heat of combustion of approximately -21.2 kJ/g. In their batch process, .25lb_mNH₃ and 5.0lb_m glucose are combined with the yeast at 25^oC. After the reaction goes to completion (at least one of the starting reactants is used up), 1. 4 lb_m of ethanol is produced. The unbalanced reaction for this process is:

C₂H₆O (s) + NH₃ (g) â C₃H₈O₃ (l) + C₂H₆O (l) + CH_1.83 O_0.56 N_{0.17 +} CO₂(g) + H₂O (l)

Note: 1 mol of glucose produces .5 mole glycerol (C₃H₈O₃₎ and that the ration of NH₃ to H₂O is 1:1.

You are told that it is likely that too much glucose is being added in the batch reactor process. It is your goal as the production engineering support specialist working for BIOFUELS INTERNATIONAL to model this scenario to determine how much unnecessary glucose is being added to reduce waste and cost.

Procedure

Follow the 4 steps of methodology for solving problems on pp. 44â46 of your textbook to set up the model.

Using MATLAB, create a plot that demonstrates the impact on ethanol production as the amount of glucose in the reactor varies from 1.0 lb_m to 10 lb_m.

Questions

How much excess glucose was being added to the reactor?

What is the ideal amount needed?

How much heat was produced and subsequently removed from the system?

Interpret the Matlab plot produced.

1.8 Methodology for Solving Engineering Problems. page 44-46. four steps.

Developing a pattern or methodology for solving engineering problems is important for consistency and thoroughness. The application of accounting and/conservation equations (discussed in Chapters 2â6) should be carried out in an organized manner; this makes the solution easy to follow, check, and be used by others. As a new engineer, you may find going through these many steps tedious and excessive for seemingly simple problems. However, when the level of difficulty increases, having a method or process to fall back on will be invaluable. Experienced engineers use most of the steps below when solving real-world problems.

The methodology laid out here or one similar to it should be used to solve problems throughout your career. The method outlined below is a general guide of the steps that will be followed to solve problems in Chapters 3â6 of this book, and as in real-world problems, only steps applicable to the problem should be performed. Other methodologies for solving problems are also valid; the critical issue is that you develop a thorough method and implement it regularly. As you mature as an engineer, it is appropriate that you develop your own problem-solving method.

1. Assemble. Information regarding the problem, including a picture, should be assembled and rewritten.

(a) The objective of the problem or the answer that you are seeking to findshould be clearly stated. This is often written as: Find: the flow rate ...

(b) Draw a diagram showing all relevant information. Often a simple box diagram showing all components entering and leaving the system allows information to be summarized in a convenient way. The system, surroundings, and system boundary should be drawn and labeled. When possible, all known quantitative information should be shown on the diagram.

(c) Set up a calculation table. The known values on your diagram, the components entering and leaving the system, form the foundation for the table. Units should be consistent across the table. The unknown components on the table (blanks) are often the desired answers. As you solve for different components, you can fill in the table. (Developing a table is optional, although useful, especially in multicomponent mass balance problems)

2. Analyze. A framework for understanding what is known and what is not known is developed at this stage.

(a) State any assumptions applied to the problem. Biological systems are extremely complex, since many processes and reactions, as well as transport of materials, are often going on simultaneously. Knowing when and where to make assumptions to simplify the system to a few salient features is the mark of an outstanding engineer. An example of an assumption is that the human forearm can be modeled as a cylinder.

(b) Collect and state any extra data. In this step, you may need to research information about a component in your system that was not given in the problem definition. An example of extra data that you may need to look up is the viscosity of plasma.

(c) List the variables and notations (symbols) adapted for the problem, and select a set of units for the problem. Typically, a choice is made to use either metric or British units throughout the problem.

[Note: The notations for variables may vary from discipline to discipline, but standard variables that are inherently understood within a subject do not always need to be listed. For example, kinetic energy is defined as EKin physics, but as T in mechanics. If you are calculating data that will be shared with coworkers of the same discipline, it is not necessary to define standard variables. Rather, variables specific to an aspect of the problem need to be defined (e.g., Fs = force of the astronaut on a chair).]

(d) State a basis of calculation. A basis is a specified input or output to a system (usually given as a flow rate or amount). In some problem statements, the basis is given. In other problems, values of components are given relative to one another and not as absolute amounts or rates. Select a basis if one is not given. Mass (Chapter 3) and energy (Chapter 4) problems often need a basis.

(e) If the problem involves chemical reaction(s), list the compounds involved and stoichiometrically balance the equation(s).

3. Calculate. Equations are developed and solved in a logical manner.

(a) Write down all appropriate accounting and/or conservation equations.Writing down the governing equations and then simplifying them by analyzing the system to eliminate unnecessary terms can be a helpful tool in solving engineering problems. For example, if asking the question, âIs this system at steady-state?â results in a positive response, the governing equation may be simplified by making the Accumulation term equal zero. This concept will be discussed further in Chapter 2. Write down any other essential equations needed to solve the problem.

(b) By applying the appropriate equations, calculate the unknown quantities. This is the heart of solving the problem and may require extensive effort. In some cases, the calculation of unknown quantities can be done sequentially. In other cases, it may be best to solve a series of equations using MATLAB or other computer software.

[Note: For a multi-unit or complex mass and energy conservation problems, a strategy to solve the problem may be required. A degree-of-freedom analysis is a systematic method to demonstrate whether a problem can be solved with the stated information and can help determine the sequence in which the equations should be solved. This process is discussed in chemical engineering textbooks (e.g., Reklaitis, Introduction to Material and Energy Balances, 1983).]

4. Finalize. Correct answers to the problem statement are stated clearly.

(a) State the answers clearly with appropriate significant figures and units. Confirm that you answered the specific questions asked by the problem

Laboratory Report Cover Sheet
DeVry University
College of Engineering and Information Sciences

Course Number: ECET301

Professor:

Laboratory Number: 3

Laboratory Title: Ethanol Production

Submittal Date: Click here to enter a date.

Write a brief technical lab report summarizing the technical facts learned from this lab. The report should be organized to provide the following:

Section 1âIntroduction: An introductory/summary paragraph describing the type of conservation principle being analyzed and the key elements that will be discussed relating to this principle.

Section 2âModel: The documented model using the standard problem-solving methodology in section 1.8 of your text.

Section 3âPlot: Matlab plot with script to generate.

Section 4âDiscussion: A section describing the most important characteristics shown, or demonstrate via the modeled and collected data. Also include a practical example of how the information learned in this assignment might help you in a job setting in the real world.

Section 5âConcluding Remarks: A summary statement listing the most positive aspects of the assignment and any difficulties encountered.

Provide a peer review

(Provide feedback relating to each rubric component (Article pros and cons, course application, defense of
position, and quality of writing). 5 points each making up 20 points.

Stoichiometry is traditionally a topic that is covered in each of the different levels at Argo Community High School (Argo). While the Honors Chemistry and Advanced Placement (AP) Chemistry courses stress a mathematical approach to mass and mole relationships, the Regular Chemistry course typically receives a lighter, scaled back approach due to a lower level of math skill and achievement. In Birdâs âStoichiometric Calculations Using Equivalent Molar Expressionsâ, the argument is made for a different mathematical approach using equivalent molar expressions instead of the standard unit or dimensional analysis method (2006). While this method does have some unique benefits for all students it would be difficult to implement completely at all levels of chemistry at Argo. One of the best aspects of using âequivalent molar expressionsâ is it shows the importance of the relationship of a balanced equation to the reacting moles (Bird, 2016). Students at Argo currently have two paths into Chemistry; a traditional biology first sequence and a nontraditional physics first sequence. The teachers in the freshman physics first sequence stress dimensional analysis throughout the course. For Sophomore Honors and AP Chemistry students stoichiometry occurs early in the semester and is continued throughout the school year. Although students have had at least one previous year using dimensional analysis, their proficiency in using dimensional analysis determines the studentsâ success or failure with stoichiometry. Students often rely on rote methods to arrive at a final answer but cannot always explain the value they calculated. Using the molar expressions method, each equivalent mole of reactant or product is determined by using the relationship of the coefficient to the starting or ending moles in the reaction. Through this method the students can see that the moles are equivalent and interchangeable, thus making a stronger connection to a particle approach to stoichiometry. Instead of a rote method of a series of dimensional analysis problems the student can quickly and easily determine the moles or other quantity desired in a balanced equation. Another positive aspect of the molar expression method is its flexibility in use with various topics. This method, combined with an ICE/BCA table (Initial, Change, End or Before, Change, After) approach, can be used to quickly inform the student of how much excess remains, how much product is formed, and what is present in the reaction vessel at the end of a reaction (May, 2017). Students in Honors and AP Chemistry at Argo struggle with determining the amount of excess reactant that remains at the end of a reaction. Various wrong methods to determine excess remaining are applied as it is a different calculation than their rote processes previously developed. Using molar expressions, combined with an ICE/BCA table, students can quickly see the amount remaining and will more accurately understand the process of the limiting reactants and the reaction itself. The students can also see that at the end there are some reactants and products remaining. Combining molar expressions with an ICE/BCA table has an added benefit of introducing ICE tables earlier in the curriculum. Although using equivalent moles can simplify stoichiometry calculations while also clarifying many mathematical misconceptions, the worst argument is the inclusion of the actual molar expression to the calculations as it is an unnecessary addition and one that would be detrimental to understanding the stoichiometry of the reaction. When students see a myriad of equations for the numerator they either quickly look for a method to memorize all of these diverse equations or simply assume it is too complicated to understand. If instead the mole was used and equivalent moles was determined instead of equivalent molar expressions, the work would become less clouded with variables. High School students may lose vigor when confronted with such a problem. Instead the students should rely on their ability to convert into moles by using molarity, the ideal gas law, or simply grams to moles, and then use equivalent moles, the process of stoichiometry can be kept separate from the method of determining moles in various ways. Using equivalent molar expressions, or just equivalent moles as I have argued, a connection can be made to both Extreme Whoosh Bottle Trio and Big Time Ethyl Alcohol Explosion videos provided by Flinn (Bracken, Dombrink, & Long, 2017; Marek, 2017). To make the demonstrations quantitative you could simply measure the amount of water generated in each demonstration. The Extreme Whoosh Bottle Trio lends itself particularly to a quantitative treatment as three different concentrations of alcohol were used. By determining the amount of water that should be generated by the 70% isopropyl solution and then comparing it to the amount of water that is actually generated, students can quickly see the application of stoichiometry as well as the use of equivalent molar expressions. The same treatement can be applied to the pure ethanol as well as the 95% isopropyl, allowing several examples as either an introduction or a summation set of demonstrations. The general idea of the equivalent molar expressions is applicable and should be used in all classes at Argo, with some modification (Bird, 2016). While the AP and Honors Chemistry students can definitely use the molar expression within the ICE/BCA table described within this paper, I have argued that the students will find it simpler without the molar expression, instead just using moles in the expression. But it would be advantageous to use molar expressions at the end of the year as a mathematical summation of several topics including percent composition, molarity, and ideal gases. However, the Regular Chemistry students would see no benefit of including molar expressions into the ICE/BCA table. The complexity of several different possible numerators would prove to be too cumbersome. Instead, it would be more appropriate to implement equivalent moles in those classes.

01:160:307 Lecture Notes - Lecture 10: Organic Chemistry, Chemical Formula, Mass Spectrometry

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