Experiment 3   The Floating Egg Problem

 

I.  Background – Working in Groups and Designing Experiments

 

Why Inquiry?

 

Chemistry is a discipline in which scientists inquire about the microscopic and macroscopic worlds around us to understand the chemical nature of our surroundings. The basis for this inquiry is experimentation in which chemists probe for answers to scientific questions we face in our world. Probably, you have heard about the so-called scientific method.  What exactly is the scientific method? Sometimes, chemists explore the microscopic world with well-established experimental techniques. More often, however, they must design their own experiments, adapting techniques to their specific problems. This is an important part of that method.  It is hoped that this laboratory experience will help you to develop important problem-solving skills necessary for success in our competitive, technological society. With guidance from your laboratory instructor, the lab handouts, and your textbook, you are free to use your creativity in solving the problems posed here.

 

The inquiry-based investigations you will encounter in this course are designed to foster your experimental problem solving skills as well as to help you learn laboratory techniques. Some of the ideas you will confront in lab will not be examined in lecture because they are issues appropriate only for the laboratory. For example, it is hoped that these lab experiences help you develop experimental design skills. These skills are not easily developed in a lecture setting. While experimental skills depend on conceptual knowledge, they differ from the concepts you will learn in lecture.

 

The textbook for the lecture component of this class will be a valuable resource in helping you relate the unfamiliar material to the problem at hand. Practicing scientists must often consult textual resources and colleagues to solve their problems. They often encounter difficulties, solutions for which are not neatly outlined in detailed laboratory procedures. Instead, they design their own experiments with the knowledge of experimental techniques in mind. Hopefully, these lab experiences will expose you to the critical thinking skills used by practicing chemists; that is, it is hoped that from the lab experience you can “learn to learn,” a skill demanded by employers of college graduates in any discipline.

 

Scientists and, indeed, members of nearly all other disciplines work in a community with others having similar interests.  Employers are demanding that undergraduate education prepare future employees for working in a cooperative, team environment. In a spirit of collegiality, these laboratory investigations are designed to maximize the contributions others can make in improving your understanding of chemistry and to prepare you for a workforce that depends on cooperative skills.  These skills include communicating ideas, negotiating with others, valuing the contribution of all group members, and delegating tasks.  During your laboratory meetings, you will draw from the understanding of your fellow students to help your group design and carry out the

investigations. The group is responsible for the success of each individual in it.

 

In this laboratory investigation and others, you will be asked to draw on your knowledge of chemical concepts as well as your interpretation of appropriate experimental procedures. Because science is often a creative endeavor, the “recipes” that often accompany laboratory experiments in general chemistry have been removed. Planning investigations is often neglected in typical recipe experiments, where the experts who wrote the lab manual do the design aspects.  These experts learned their experimental skills by trial, error, creativity, serendipity, and knowledge of chemical behavior.  By removing the recipes the goal is to encourage you to develop these critical skills. You are responsible, together with your fellow group members, for the overall planning of the experiment which includes the design, data collection, organization, interpretation, and communication of your laboratory investigations. This accountability will at times be frustrating because you may not feel intellectually equipped to complete the investigation. However, once you draw on your understanding of the world, the chemistry you have learned so far, and the experience of others, we are confident that you will find the investigations rewarding.

 

Your Group

 

Most companies have an organizational structure that is team based.  Employers have found that in a team-structured environment, gains are made by people putting their heads together to solve problems.  In educational settings such as this one, group-based, cooperative learning efforts improve relations across different cultures and genders, increase student retention, and generally improve student performance.  In industrial, governmental, and educational institutions, group work often has at least four characteristics:  (1) the group works toward a common goal, (2) the group is responsible for success of each member, (3) each member is individually accountable for completing various tasks and gaining relevant knowledge, and (4) the group members share resources.  Your lab instructor may assign you to a group, the members of whom you may have nothing in common with socially.  However, successful team efforts often rest on the ability to draw from the experiences of people from diverse backgrounds.

 

To facilitate your group’s success, each member could assume one of the following roles:

 

Team leader – coordinates the activities of group members including the generation of reports.

Assistant leader – keeps the group on-task. Consolidates from group members supporting literature relevant to the investigation. Monitors group activities so all members contribute in a healthy, supportive environment.

Data collection expert – directs the data collection activities for the group. This includes identifying the information that must be collected and recording the data in an appropriately organized manner.

Experimental technique expert – determines the appropriate reagents and equipment assembly for data collection. Consults with instructor for special instructions about equipment.

 

Even though you will assume various roles, each group member is expected to contribute to experimental design discussions.   If other labs of this nature are performed in this course, you can rotate the roles so all group members have an opportunity to develop the skills associated with that role.

 

Because each member of your group is individually accountable for successful completion of the class assignments, you will be asked to describe your contribution to the investigation. At the end of this investigation is a contribution form that must be completed by every member of the group. On that form you will report your percent effort as well as your perception of what other group members contributed. In addition, you will also describe what you did to help your group complete the investigation and write the report. The contribution forms are due at the same time as your report.

 

 

Writing Proposals

 

In this investigation, you will be presented with a problem that you are asked to solve.  The first phase of your lab work will involve designing experiments to solve the problem posed. This is often a non-trivial task, so you can expect it to take some time. The issues you must consider will involve the following:

 

· Equipment issues.  What types of equipment will be required to enable you to complete your experiment?

· Reagents.  What chemicals and quantities will you use that will enable you to complete your experiment?

· Variables to control.  How will you design your experiment so that only the variables your are interested in affect your results?

· Data to collect.  Specifically, what data will you collect as you perform your experiment that will help you solve your problem?

· Analysis of the data. In what way will you analyze the data to arrive at your conclusions about the problem posed?

·Safety considerations.  What precautions must you take to ensure the safety of your group and other members of the class?

· Waste disposal. How will dispose of any waste that is generated or any leftover reagents from your investigation?

 

Some initial exploration of the chemistry involved before formal experimental planning can be completed may be necessary. You can use your preliminary exploration to design your experiments, if necessary. If initial experimentation is necessary before you submit your proposal, you should brief your instructor on what you will do during your exploration so that safety concerns can be addressed.

 

Once your group has decided upon an experimental design, you must submit a proposal to your instructor. Your group should write a proposal in one of your lab notebooks or on a separate sheet of paper, as instructed by your instructor.  The written structure of the proposal is at your discretion unless directed otherwise by your instructor.  However, your proposal must include the following:

 

· Clearly state your experimental methods, including addressing the points listed above.

· A description what you expect to see in the form of hypotheses.

· A discussion of how these procedures will yield a solution to the problem.

 

Whether or not your instructor signs off on your proposal will depend on whether or not your proposal contains the items listed in the above paragraphs.  If your proposal is incomplete, expect to be sent back to your group to more thoroughly think through your experimental design. Note that your proposal will not necessarily be evaluated on your specific method, but rather on how well your design is thought out and follows the above guidelines.

Finally, remember that at this point in your learning process, you and all your classmates are still novices.  Your instructor understands this and is there to guide you in developing these skills.  That is one of the goals of this lab.  Do not be discouraged if it takes time to become skilled in this process.  Good luck and have fun!

 

 

 

 

 


 

II.  Background – The Floating Egg Problem and Volumetric Glassware

Introduction

 

For many years soap was made at home from a variety of recipes.  Animal fat, usually from cattle was cooked with a lye solution.  Lye, though it was mostly simple sodium hydroxide (today commonly found in drain cleaners) could not be made from purified chemicals, as we do now.  Instead, the solution was obtained from ashes and water.  The ashes were treated with hot water, and then the mixture was filtered to obtain a solution.    But before this could be used for soap making, one had to check the concentration of the lye solution.  One simple test was to try to just float a raw egg in the solution.  If the egg sank, the concentration of the lye in the solution was too low.  If the egg floated too high, the concentration was too great, and water was added before adding the fat.  To “just float” in this case means to make the top of the egg just touch the top of the solution, without any significant amount of the egg protruding above the surface of the solution. 

 

Imagine that your friend in the Peace Corps has been working with the local population of a remote village in a developing country to set up a manufacturing facility to produce soap.  The village is able to acquire an inexpensive supply of lye as a byproduct of a different manufacturing operation in a larger city.  As the village does not have an analytical chemist on hand, your friend has contacted your group to provide the village with a recipe for the amount of lye (in grams) to add to a volume of water to use in their soap making facility. 

 

Note:  Because lye is caustic and corrosive, the substitute sodium chloride (NaCl) (common table salt) will be used in this lab.  The solutions are still concentrated enough to pose hazards to the eyes.  Be aware of any safety precautions.

 

Goals

 

As you complete this investigation you will:

 

1. Determine the density (in grams per milliliter) of the solution needed for the production of soap.

2.  Produce a recipe for the amount (in grams) of sodium chloride (NaCl) needed to be mixed with 100 kg of water for the production of soap.

3.  Determine the mass% of the NaCl solution.

4.  Determine in which way the type of the following volumetric glassware used affects the value and accuracy of the calculated density:  1) volumetric pipet, 2) Mohr (measuring) pipet,  3) buret,  4) volumetric flask.

5.  Write a final report that summarizes your findings (and that theoretically would be sent off to your friend in Peace Corps).

 

Materials

 

Sodium chloride (NaCl)

Eggs

Standard glassware

Volumetric glassware:  burets, Mohr pipets, volumetric pipets, volumetric flasks

Other items available on request

 

Getting Started

 

Chemists use special volumetric glassware in the laboratory (rather than the ordinary beakers and flasks) when they need high-precision measurements of the volume of liquids.  Understanding the proper use and limitations of such glassware is important in achieving reliable results.   Experimental technique and the inherent accuracy of the glassware both affect experimental results.  One of the goals of this course is for you to develop sound experimental techniques.

 

In this investigation, you will practice with volumetric glassware to improve your technique and to solve an important historical question in practical chemistry.  Volumetric glassware is designed for two quite different purposes. 

 

·  To deliver (TD) an accurate volume of liquid.

·  To contain (TC) an accurate volume of liquid.

 

A container meant to contain an accurately known volume could of course be used to deliver the liquid to another vessel.  However, the amount actually delivered would never exactly be equal to the amount originally in the container.  Some liquid would inevitably remain behind, clinging to the interior walls. Some liquid also remains behind on the walls of a piece of glassware that is TD designed, but the calibration of the TD glassware takes this into account.

 

The following guidelines must be followed:

 

  1. Make at least 1000 mL of the solution.
  2. Use only 1 egg for testing.
  3. Once you have produced a solution that will “just float” an egg, you are to determine its density and mass% using the 4 types of volumetric glassware:
    1. Your instructor will demonstrate the correct procedure for using each type of glassware.
    2. Develop procedures to determine the density of your solution using each type of glassware.
    3. Repeat the measurements using each type of glassware a minimum of three times.  Determine the STD or average deviation for each measurement.
  4. Each individual in your group should use all four kinds of measuring devices at least once.

 

 

 

Report

 

 

Reports should be constructed in the format given in the introduction of the first week’s lab (Recording and Analyzing Experimental Data, Graphing Techniques), to the extent that this format is appropriate for the experiments that you designed.   This is the format that chemists use to report the results of their experiments to the scientific community.  The emphasis of this report is on your determination of the density of the solution and your recommendation to your Peace Corps friend on how to produce the solution.  In your procedure section, it is acceptable to insert a copy of your proposal.  The analysis should include answers to the goal questions, and also an indication of the difference in the precision and/or accuracy of the 4 types of volumetric glassware (Which had the largest STD or average variation?  How did your results compare to others in the classroom?)