Chemistry:

CHM 1025C/CHM 1032C

 

Laboratory Manual

 

Fall 2010 Term

 

 

Written, modified, and/or adapted by

Professor John Taylor, Dr. Joseph Langat,

and Dr. Kathleen Laurenzo

 

Reviewed, Edited and/or Revised by

Dr. Marcelle Bessman, Dr. Stephen Lukacs, Dr. Vandon White,

 Dr. Terry Waggoner, Dr. George Odongo, Dr. Reed Freeman,

Dr. Julie Sutton , Professor Thomas White,

 Dr. Paula Thompson, and Professor Rhoda Yost

 

Some Content Originally Supplied by:

Dr. Andrea Wallace, CGCC and Dr. David Summers, USAF Academy

 

Florida State College at Jacksonville

North Campus

Jacksonville, Florida

   Fall 2010 Tentative Laboratory Schedule (A-16)                                                   

 

 

 

 

 

Week                                                                                        

 

1.  Welcome/Laboratory Notebook                                                       

       Lab Safety Film Notes

       Lab Safety Rules and Safety Contract

       Laboratory Diagram

       Laboratory Equipment

       NFPA and HMIS Safety Codes

 2.    *Video The Scientific Method/Controlled Experiment:

           Analysis of the “Andromeda Strain” Movie

 3.   Introduction to Measurement/Metric System                                 

        Gasoline Project (Optional)

 4.    Density (and Specific Heat Option)

                                                      

 5.   Graphing Data

                                                                                   

 6.   Chemical and Physical Properties

                               

 7.   Atomic Spectra/Dot Structures/Nomenclature                                                  

 

  8.   Cation Analysis

                                                                                 

  9.  Anion Analysis and/or Case of the Six White Powers

 

10.   Analysis of a Hydrate

                   

11.  ** Video “Who Killed the Electric Car”

 

12.  Alka Seltzer Analysis

 

13.  REDOX Challenge Contest or Preparation of Aspirin or Acid/Base Titration or Molecular Mass of a Gas via Vapor Density or No wet lab

 

14. Air bags and Gas Laws

 

15. Organic Structures and Isomer Number Problems

 

16. Laboratory Practical   (Optional)    

 

 

 

 

CHM 1025C/CHM 1032C

Laboratory Guidelines

 

As you know from your syllabus, your chemistry labs will account for 20% or more of your final grade in this course.  As such, it would be in your best interest to complete your lab work in a timely and conscientious manner.  The following is a set of guidelines which will help you make the most of your lab grade:

 

1)         Welcome to college: coherent sentences required.  Points will be deducted for incorrect spelling, bad grammar, and other miscellaneous abuse of the English language.

 

2)         Watch your values.  Significant figure and rounding errors will result in appropriate deductions, in both data and calculations.  If you are not sure how to round a number or how many significant figures you should have, ASK.

 

3)         Your Lab Instructor/Assistant are not cryptographers.  If we cannot read your handwriting, we will assume that you have the wrong answer.  Do not cram data or answers in the margins of your lab manual; use a separate sheet of page of your lab notebook and indicate the question number or label your data appropriately.  If we have to guess, we will guess that you are incorrect.

 

4)         Poor results will result in significant deductions.  Do your work carefully, paying close attention to precision and accuracy, and asking questions BEFORE a crisis occurs.  Always remember that doing the lab slowly but correctly the first time takes much less time than doing it wrong and having to do it over.

 

5)         Late work will be penalized by at least 20 percent deduction per week (option of your instructor) unless authorized by the instructor, so turn your work in on time for full credit.  This point deduction is subject to increase at your instructor’s discretion.  Pre and post labs are due at the beginning of the lab, not 5 minutes after lab starts.  Your work will be considered late if it is not submitted as you enter the lab.

 

6)         Values without units mean absolutely nothing, so make sure to add the appropriate units to all values unless they are provided for you on the report sheet.

 

7)         Failing to write your name on your lab means more guesswork for your lab instructor/assistant…and an automatic 25% penalty.

 

8)         You are required at least INDIVIDUALLY to work each experiment except when directed you will work with a partner. (Not partners). There are six lab tables with 24 stations, but when working in Pairs two experiments per table (Not three or Four). Students preferring to work individually will be allowed to do so. If an odd person come to lab, than for being late that person MUST work alone (Not join a group)

 

9.  Copying results and/or answers from anyone WILL NOT be tolerated.  Even if you and your partner work together on the post lab, if you can’t find an original way to show your calculations or word your answers, chances are you don’t understand it anyway.  Any copying will result in a deduction of the total points possible for all values and/or answers that were copied.

 

CHM 1025C/CHM 1032C

 

Welcome to the Chemistry Lab D-204

 

Introduction

 

The experiments in this lab manual have been chosen to introduce you to some basic and important laboratory equipment and techniques.  In addition, some of the experiments provide an opportunity for you to test your laboratory skills by analyzing “unknown” samples.  Each experiment is designed to be completed within a two-hour period.  You should be able to complete the work in the time allotted.  This time allotment does assume, however, that before coming to the laboratory you have read the introduction to the experiment, completed the prelab report, have answered the pre-laboratory problems (which introduce needed concepts), and have carefully read the experimental procedure.

 

Laboratory Notebook and Reports

 

Student Must purchase a Laboratory Research Notebook in the bookstore,

ISBN #r 9781930882508 for ~$12.50. All students must use this Notebook. This notebook has 50 NCR duplicate pages. One page will remain in your notebook as a permanent copy, the other is designed to be torn out and submitted to your instructor. A lab report must be submitted for each experiment that you perform. 

 

For most experiments, the report will be in three parts: 

(1) the pre-lab due at the beginning of the lab period,

(2) the data and observations collected while in the lab, and

(3) the calculations and post-lab questions to be completed after the procedure. 

 

The majority of the labs in this manual have a data recording and report sheet created for you to copy in your Laboratory Research Notebook as part of your pre-Lab Activity.  If no report sheet is provided, you must create your own in your laboratory notebook.

 

All submitted recordings and reports must be neatly handwritten, and should contain the following elements, when applicable, in the order given:

 

Pre Lab (do NOT  tear out your pre-Lab report from your notebook unless directed to do so. Your instructor will initial your pre-lab report during the beginning of lab and put a time you entered the lab):

 

1. Your name, section number, and date.

 

2. The title of the experiment and the date on which it is performed.

 

3. Every lab will have a prelab report which includes the Objectives or Goals copied in your lab notebook. Your instructor will direct you if you have to also Outline the lab and/or copy a summary of each procedure.

 

4. Students coming to lab, who have not read the experiment or prepared the prelab report WILL NOT BE ALLOWED to work in the lab that day.

 

5. Students who do not have their lab notebook will NOT be allowed to work in the lab that day.

 

6. Students will submit to the instructor when they enter the lab, their prelab report. The instructor will initial the acceptance of the prelab report and also note the time the student submitted the work. Student should then sign the attendance role with the time entered the lab..

 

7. For example, the second week of lab will be measurement and the introduction to the metric system should at least contain the following::

 

----------------------------------sample prelab week 2--------------------------------------

 

Pre-Lab Report: Experiment 2

          LABORATORY MEASUREMENT - THE METRIC SYSTEM

 

Measurement GOALS:

 

(1) To learn to manipulate laboratory instruments to measure length, mass, volume, count, and time.

 

(2) To introduce the relationship of the metric units to English units.

 

(3) To learn the difference between precision and accuracy.

 

(4) To learn to calculate a deviation and a per cent error in experimentation.

 

Your instructor will tell you what additional information she/he wants in this prelab report.

 

 

----------------------------------sample prelab week 3--------------------------------------

 

Pre-Lab Report: Experiment 3

Density and Measurement

 

Density  Lab GOALS:

 

1.      To measure liquid volume as accurately as possible with graduated cylinders.

 

2.      To measure the volume of irregular shaped solid objects by liquid volume displacement.

 

3.      To measure liquid volumes by pipetting into containers.

 

4.      To weight objects as accurately as possible on a Top Loader Balance.

 

5.      To weigh objects to six significant figures on an analytical balances.

 

6.      To calculate the density of known and unknown solids and liquids by measuring the mass and the volume of the objects with lab instruments.

 

7.      To observe experimental deviations through error of instruments or students.

 

8.      To introduce the terms accuracy, precision, reliability, sensitivity as related to an analytical procedure.

 

9.         Answers to any pre-lab problems must be written in your notebook. Your instructor will request you to submit the hard copy handout-filled out before the lab. Then the actual data recording page must be neatly laid out in your notebook.

 

Data and Observations:

 

10.       All data and observations are to be entered directly into your notebook as you go through the experiment.  Each student must record his/her own data.  Do not use a sheet of paper and then transcribe the data into the notebook later.  Do not record data on any sample  datasheet you are given. Neatness is important, but honesty and accuracy are equally as important.

           

            Numerical data must be identified by a tag (e.g. “mass of Erlenmeyer flask – empty”) and include units (g, mL, etc.).  Use the correct number of significant figures to report your data.

 

For example:

            Mass of empty Erlenmeyer flask            52.650 g,   not 52.65

            Mass of flask + benzoic acid                 53.000 g,   not 53

 

            Note that you record both masses, not just the difference between the two.  Similarly, for measurements with a buret, you should record both the initial and final buret readings, not just the difference between them. See the sample Data Recording Sheet provided with the experiment. (You first two buret readings must be initialized by your instructor as with many of your other first reading with measuring equipment.)

 

All data is to be entered in ink; no pencils and no erasures.  If an error is made in recording data, draw a single line through the mistake, correct it nearby and initial the correction.  Do not obliterate any entry.  If a substantial portion of a page is to be discarded, cross the material out with an X.

Neatness and care in recording data and calculations are a plus, but it is more important that the notebook be an immediate and permanent record, “warts and all”, of everything that happened in the lab.

Turn in your duplicates with your report. 

NOTEBOOK ORGANIZATION

11    Title Page: List your name, address and phone number along with the course section and instructor name. At the bottom, Copy the Lab Safety Contract and sign it.

Table of Contents: fill in the list of experiments as you go into the cover which has the Table of Contents.  List the date, title and beginning page number of each experiment.  You will turn this in at the end of the semester

Before coming to the lab, read the experiment to be done and do the prelab exercises.  In your notebook, write a title and the date of the experiment, a brief statement of purpose.  Make notes in your notebook and work out a tentative procedure and data tables to be filled in.  This is called “preparing your notebook to accept data” and will save you time as well as organizing your thinking.  It is usually not possible to anticipate everything.  Make any corrections and additional observations as you work through the lab.

Experiment #1 Safety Lab and Lab Orientation

a. On page 2 of your lab notebook you will begin the Safety Lab. At the top of the page place your name, section number and the date. Then, place the title:

Safety Lab

b. Then place a subheading: ACS Safety Film Notes:
As you watch the film, record notes or emphasized statements which will become a rough set of safety rules.

c. Make a rough sketch of the room in your notebook. Label on the sketch the following: Safety shower, emergency eyewash, safety blanket, goggle/glasses cabinet, first aide kit, two major wash up sinks for hand washing and hardware equipment drawers identified by the instructor.

d. On a new page (page 3) as a post lab report, list at least 20 or more lab safety rules from the three handouts and the ACS film. 

          

e. On the separate page (page 4) of your lab notebook Sketch the NFPA symbol and then copy a more detailed or specific hazard for each NFPA numeric category from the Safety Codes handout. Explain what each number represents in each category

 

f. In your lab notebook on a separate page (Page 5) sketch the HMIS Labeling System and list the descriptions for each number for each category.

 

g. In your lab notebook (at the bottom of page 5), state the purpose behind both system and why they are different.

 

h. Using Chemical Date Bases on the Internet, copy on a new page (Page 6) in your notebook the data sheet from the MSDS Assignment handout and fill in the form for the chemical assigned and submit this page by the second lab period.

 

(Instructor’s note: Safety Lab will be the longest report in this course as it requires a lot of copying of information you may need during a lab and/or handling chemicals. Most reports are usually only one, two or three pages in length depending on the calculations.)

 

Final Report – Non Formal:

 

12.       If you have copied a printed report sheet from this manual you have two copies in your research notebook. Include a copy of this data and its summary in your final report.  Also include your name, section number, and date on every page.

 

13.       Calculations:  There should be a separate section devoted to the calculations unless the data report sheet has left room for a simple calculation, such as the Density Lab.  Otherwise, the calculations should be completely separate from your data and results.  You must show every mathematical calculation that you perform.

 

14.       Answers to any Post Lab questions and/or conclusions belong on separate page in your notebook unless ample room is obviously provided.

Final REPORTS – Formal:

Most of labs include a datasheet that will serve as your non formal report. However there will at least one lab, usually the last week, requiring a more formal report.  The following format should be used.

A.   Title: the name and number of the experiment, name of your lab partner(s), if any, and the dates of the experiment and of the report.

B.   Purpose or Abstract: a statement describing the major goals of the experiment.

C.  Procedure: describe how you went about the experiment.  Usually a reference to the handout will suffice; however, you should mention any changes or deviation from the procedure as given to you.  Rewriting the whole procedure is an unnecessary duplication of effort.

D.  Data: record, in tabular format where possible, all pertinent data collected, calculated values and results.  It is often appropriate to have two tables, one for original data and another for results.

E.  Calculations: show equations and calculations used to arrive at final results. A general formula and one example are sufficient for repetitive calculations.  Include here any required graphs.

F.  Conclusions:  discuss the results of the experiment and how they relate to the concepts in the reading material.  Was the stated purpose achieved?   If not, why not?  Include a discussion of major possible errors and their impact on the experiment.  The conclusion section is the most important part of the report and has the most influence on your grade.  The prelab mini-lecture will give you information about the important points of the lab.  Listen carefully and take notes.

G.    Post-lab: Answer any questions or exercises included as part of the experiment.

 

15. Pre and Post Lab calculations are designed to be performed individually, with the answers given to the correct number of significant figures and with the correct units.

 

16. Pre and Post Lab questions are designed to be answered individually.  Answers should be concise, legible, and in your own words (do not plagiarize or otherwise copy from texts, websites, or your classmates).

 

 

Sample Safety Contract – Lab Notebook Page 1

 

Exp #:

One

Experiment/Subject:

Laboratory Safety Contract

 

Title Page

Date:

    /    /10

Page 01

 

 

Name:

Lab Partner:    

Course:

CHM 10__ C

Section #

 

 

Name: _________________________         Email: ____________________________

 

Address: _______________________          2nd Email: _________________________

 

_______________________________         Phone #: __________________________

 

                         __________________          Cell Phone: ________________________

 

 

Course:  CHM 1025C/CHM 1032C

Section #: __________

 

Professor: _______________________

 

I, ____________________________, have watched the ACS Laboratory Safety Film. I have read four different sets of Safety Rules from various colleges provided by my instructor. I have synthesized from these rules and the safety film a list of at least 20 rules written in this Laboratory Notebook which I agree to abide during all formal laboratory activities and experiences in FSCJ North Campus’s D-204 Chemistry Lab. I agree to wear proper safety glass at all times during lab activity, regardless if I, myself, am not currently performing any activity. I agree to lose points on my current lab if I am not wearing these safety glasses. I understand that protective aprons, gloves and lab coats are available at my option to use during formal lab activity. I have sketched in this laboratory notebook, the layout of the North Campus Chemistry Lab D-204 and have noted the placement of all safety features, equipment and supplies in this Post Lab Safety Report.

 

Signed: _______________________Date:________________

 

Signature:

Date:

Witness/TA:

 

Date:

Florida State College @ Jacksonville                                North Campus

          

 

Fall 2010 Chemistry Schedule

                           – FSCJ North Campus –

 

The following are the scheduled CHM 1025C and CHM 1032C Courses at North campus. All three CHM 1025C sections and the four sections highlighted of CHM 1032C will be doing the same experiment each week. If you are absent from a lab there is no makeup. However, with the permission of your instructor and the other scheduled lab instructor, you may on an emergency basis attend and complete that weeks lab at an alternate time.

 

CHM 1025C

CHM1025C - Introduction to General Chemistry

4 Credits

Additional Fee: $15

Description: This course is an introduction to the concepts of inorganic chemistry including structures of matter, atomic theory, nomenclature, bonding, gases, solutions, equilibrium, and acids and bases. This course is for students who have had no previous chemistry and plan to major in science, engineering, pre-medicine or pharmacy.
Prerequisites: MAC 1105 or satisfactory score on placement test.
Corequisites: None.

327110

NORTH CAMPUS

D0203

1:30PM to 3:30PM

MW

8/30/2010 - 12/17/2010

TAYLOR, JOHN T

 

NORTH CAMPUS

D0204

11:15AM to 1:15PM

M

8/30/2010 - 12/17/2010

TAYLOR, JOHN T

327111

NORTH CAMPUS

D0203

1:30PM to 3:35PM

TR

8/30/2010 - 12/17/2010

WAGGONER, TERRY B

 

NORTH CAMPUS

D0204

11:15AM to 1:15PM

R

8/30/2010 - 12/17/2010

WAGGONER, TERRY B

327112

NORTH CAMPUS

D0204

11:15AM to 1:15PM

T

8/30/2010 - 12/17/2010

LANGAT, JOSEPH K

 

NORTH CAMPUS

D0207

9:00AM to 11:00AM

TR

8/30/2010 - 12/17/2010

LANGAT, JOSEPH K

327113

NORTH CAMPUS

D0204

7:30PM to 9:30PM

W

8/30/2010 - 12/17/2010

LANGAT, JOSEPH K

 

NORTH CAMPUS

D0205

5:00PM to 7:05PM

MW

8/30/2010 - 12/17/2010

LANGAT, JOSEPH K

327118

NORTH CAMPUS

D0204

5:00PM to 7:00PM

W

8/30/2010 - 12/17/2010

WHITE, VANDON E

 

NORTH CAMPUS

D0209

7:15PM to 9:15PM

MW

8/30/2010 - 12/17/2010

WHITE, VANDON E

327119

NORTH CAMPUS

D0204

1:00PM to 3:30PM

S

8/30/2010 - 12/17/2010

WHITE JR, THOMAS C

 

NORTH CAMPUS

D0207

8:30AM to 12:30PM

S

8/30/2010 - 12/17/2010

WHITE JR, THOMAS C

334972

NORTH CAMPUS

D0204

9:00AM to 11:00AM

W

8/30/2010 - 12/17/2010

LUKACS JR, STEPHEN J

 

NORTH CAMPUS

D0205

9:00AM to Noon

M

8/30/2010 - 12/17/2010

LUKACS JR, STEPHEN J

 

NORTH CAMPUS

D0205

11:00AM to Noon

W

8/30/2010 - 12/17/2010

LUKACS JR, STEPHEN J

 

 

 

 

 

 

CHM 1032C

CHM1032C - Principles of General Chemistry

4 Credits

Description: Students will benefit by taking high school algebra or MAT 1033 prior to enrolling in this course. This course is an introduction to the concepts of inorganic chemistry including structures of matter, atomic theory, nomenclature, bonding, bases and introduction to organic chemistry. This course is for students who have had no previous chemistry and plan to major in dental hygiene, medical technology, nursing or health related fields.
Prerequisites: None.
Corequisites: MAT 1033 or satisfactory score on the placement test.

327117

NORTH CAMPUS

D0203

Noon to 4:00PM

S

8/30/2010 - 12/17/2010

ODONGO OMALLA, GEORGE

 

NORTH CAMPUS

D0204

9:00AM to 11:30AM

S

8/30/2010 - 12/17/2010

ODONGO OMALLA, GEORGE

327121

NORTH CAMPUS

D0209

9:00AM to Noon

F

8/30/2010 - 11/21/2010

LUKACS JR, STEPHEN J

 

This is a Hybrid course. Registering for this Hybrid course requires students to rely heavily on reading the textbooks, supplements, and materials. This is a more self-disciplined, self- guided and self-taught course. Class will meet once a week during the scheduled time at North Campus for recitation, discussion, issue resolving and problem solving. Lectures are online. Students must have a stable computer and internet access.

327122

NORTH CAMPUS

D0203

5:30PM to 9:30PM

W

8/30/2010 - 11/21/2010

LUKACS JR, STEPHEN J

 

This is a Hybrid course. Registering for this Hybrid course requires students to rely heavily on reading the textbooks, supplements and materials. This is a more self-disciplined, self-guided and self-taught course. Class will meet once a week during the scheduled time at North Campus for recitation, discussion, issue solving and problem solving. Lectures are online. Students must have a stable computer and internet access.

327125

NORTH CAMPUS

D0204

11:15AM to 1:15PM

W

8/30/2010 - 12/17/2010

WHITE, VANDON E

 

NORTH CAMPUS

D0207

9:00AM to 11:00AM

MW

8/30/2010 - 12/17/2010

WHITE, VANDON E

327128

NORTH CAMPUS

D0204

2:30PM to 4:30PM

T

8/30/2010 - 12/17/2010

WHITE JR, THOMAS C

 

NORTH CAMPUS

D0207

12:30PM to 2:30PM

TR

8/30/2010 - 12/17/2010

WHITE JR, THOMAS C

327133

NORTH CAMPUS

D0204

5:00PM to 7:00PM

M

8/30/2010 - 12/17/2010

SUTTON,

 

NORTH CAMPUS

D0212

7:45PM to 9:50PM

MW

8/30/2010 - 12/17/2010

SUTTON,

327138

NORTH CAMPUS

D0204

8:30AM to 11:00AM

M

9/27/2010 - 12/17/2010

WAGGONER, TERRY B

 

NORTH CAMPUS

D0212

8:30AM to 11:10AM

TR

9/27/2010 - 12/17/2010

WAGGONER, TERRY B

328653

NASSAU COUNTY CTR

A0207

9:00AM to 11:00AM

TR

8/30/2010 - 12/17/2010

LUKACS JR, STEPHEN J

 

This is a hybrid course. Registering for this course requires students to rely heavily on reading the textbooks, supplements, and materials. Class will meet on Tuesdays and Thursdays at the Nassau Center for recitation, discussion, issue resolving, and problem-solving. Lectures are online, Students must have a stable computer and Internet access.

B-12 class

333870

NORTH CAMPUS

D0204

11:30AM to 1:00PM

S

9/27/2010 - 12/17/2010

WHITE, VANDON E

 

NORTH CAMPUS

D0212

9:00AM to Noon

S

9/27/2010 - 12/17/2010

WHITE, VANDON E

 

NORTH CAMPUS

D0212

12:30PM to 4:00PM

S

9/27/2010 - 12/17/2010

WHITE, VANDON E

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Laboratory Safety Rules

(main source: Dr. David Summers)

 

 

Laboratory accidents can result in loss of time, damage to clothing and other property, and personal injury.  By following suitable precautions, you can anticipate and prevent situations that could lead to accidents.

 

You must make yourself completely familiar with the following safety rules.  You will be required to sign a Laboratory Safety Contract stating that you have read these rules, agree to abide by them, and have watched the ACS Safety Video.  At the beginning of the second laboratory period you may (instructor’s option) take a short multiple-choice and/or true false quiz on the rules; if you miss more than one question, you must pass a retest before you will be permitted in the laboratory. In your lab notebook copy at least 20 safety rules from the three handouts and the ACS video. Then copy the Laboratory Safety contract at the bottom of the first page and sign it plus submit to your instructor the one to be held on file at FSCJ’s Laboratory Supervisor’s office.

 

Rules

 

  1. Do not work in the lab unless the lab assistant/supervisor or instructor is present.  No unauthorized experimentation is allowed.

 

  1. Work carefully with full awareness of what you are doing, so as to avoid dropping or breaking equipment or spilling chemicals.  Keep reagents and equipment well back from the edge of the lab bench.  Never run in the lab.

 

  1. You may provide your own pair of safety glasses/goggles and wear them in the lab at all times or you may wear the eye protection glasses available in the cabinet in the lab room D-204. Safety glasses MUST meet or exceed ANSI Z87.1 (this should be indicated on the packaging).  A lab apron or lab coat should also be worn at all times while working in the lab.

 

  1. You must wear shoes without open spaces; sandals and open-toe shoes are not acceptable.

 

  1. Confine long hair and neckties; they may catch fire, get into chemicals, or get caught in apparatus.  Loose jewelry or rings can also be a hazard.  Frilly or flared clothing, especially synthetics, are not safe around flames unless covered with a lab apron or coat.

 

  1. Do not bring food or drink into the lab.  No eating or smoking is permitted in the lab.

 

  1. Never taste a chemical.  Smell a chemical by fanning the air over the container to waft the vapor to your nose; never smell directly.  Do not touch chemicals with your hands unless specifically directed to do so; if contact occurs, immediately flush the area with cool water.

 

 

 

  1. Mercury vapor is invisible but toxic over time.  A broken thermometer should be reported immediately to the instructor.

 

  1. Never look directly into an open vessel in which a reaction is occurring that could cause spattering.  When heating materials in any container, be sure that the open end does not point in the direction of other persons or yourself.

 

  1. If any chemical gets into your eyes, flush with water for at least 15 minutes.

 

  1. In case of fire, turn off the burner first.  If there is a fire in a beaker, try to smother it with a watch glass or wet paper towel placed over the beaker.  For an open flame, use the fire extinguisher pointed at the base of the flame.  If the fire is uncontrollable, close all windows and evacuate the room and pull the fire alarm located near the emergency exit or in the hallway.  After evacuating to a safe place, call 911, and campus security @ 766-6008 if you instructor is not present..

 

  1. Skin burns should immediately be placed under cold running tap water for 5-10 minutes in order to remove the heat.

 

  1. If clothing catches on fire, use a fire blanket or safety shower.

 


  1. Do not force a glass tube or thermometer into a stopper; the glass can break and gash or stab you.  Instead, lubricate the end of the glass with glycerin; hold both the glass and the stopper with a cloth towel to protect your hands; grasp the glass close to the stopper; insert with a slow twisting motion (see figure below).
  2. Report all accidents and injuries to the instructor as soon as emergency action has been initiated.

 

  1. Never place chemicals directly on the balance pan.  Instead, use a beaker, flask, watch glass, or piece of weighing paper.

 

  1. Read the label on a bottle twice before using the contents.  Never contaminate the contents of a bottle by putting reagents back into it.  Do NOT waste reagents; if you take too much, share it with others who still need your chemical.

 

  1. Label any sample or mixture that you prepare.

 

  1. Never mix any reagents unless specifically directed to do so.

 

  1. When mixing water and acid, always add acid to water otherwise violent spattering may occur.  Remember the word “acid” alphabetically comes before “water,” so acid-into-water.

 

  1. Dispose of waste chemicals as directed.  If a waste container becomes full, tell the instructor or lab assistant so they can get an empty replacement.  Don’t just ignore the situation.

 

  1. Do not use cracked glassware, as it may break when stress is put on it.  Place broken glassware in specifically designated containers in order to prevent injury to the cleaning personnel.

 

  1. If you discover that bottles of chemicals need to be refilled, tell the instructor or lab assistant.

 

  1. Keep the lab bench and tables clean.  Wipe up all spills.  Acid spills should be neutralized with sodium bicarbonate (which can be obtained from your instructor or lab assistant).

 

 

 

 

 


Laboratory Safety Rules-CGCC

 

1.     Wearing approved safety goggles is required at all times while in the lab. 

2.     Be aware of what is going on around you.

3.     Unauthorized experiments are prohibited.

4.     Follow directions carefully.

5.     Food and beverages are prohibited in the lab.

6.     Clothing which protects is necessary.

7.     Locate the fire extinguisher, eye wash, safety shower, and first aid kit.

8.     Know how to operate all safety equipment.

9.     Never pipet by mouth, taste chemicals, or directly smell chemicals.

10. Avoid chemical contact with skin, eyes, and clothing.

11. Read chemical labels thoroughly and observe all precautions.

12. Never return chemicals to a reagent bottle unless told to do so.

13. Never pipet directly from a reagent bottle.

14. Do not carry reagent bottles to your desk.

15. Do not weigh chemicals directly on to the balance.

16. Dispose of chemicals in proper containers, according to directions from the instructor.

17. Never point a test tube containing a reacting mixture towards yourself or another person.

18. When inserting or removing glass tubing, protect your hands with a towel and gently twist, never force.  Use glycerin for lubrication if necessary.

19. Keep a neat, uncluttered laboratory bench.

20. Place broken glassware in the designated container.

21. Report all accidents such as burns, cuts, chemical spills, etc.

22. A burn should be treated immediately by washing it with cold water.

23. Do not remove chemicals or equipment from the lab.

24. Make sure gas and water are turned off before leaving the lab. 

25. Always wash your hands before leaving the lab. 

 

 

Obtain Separate Set of Safety Rules from Old CHM 1015 Lab Manual or FSCJ old Handout for the third set to review.

Safety Codes

Hazard Codes

            ChemAlert rates hazards numerically inside the NFPA (National Fire Protection Association) diamond.  This symbol was chosen for its universality.

            The diamond has a red segment (flammability), a blue segment (health, i.e. toxicity), a yellow segment (reactivity), and a white/blank segment (special warnings such as radioactivity or no water).  Printed over each is a bold black number expressing the degree of the hazard.

            The numerical ratings are:

     4 = extreme hazard

        3 = severe hazard

        2 = moderate hazard

1 = slight hazard

                                 0 = according to present data, none

Storage Codes

The storage code is assigned according to the chemicals worst hazard:

RED               Flammable

YELLOW       Reactive and Oxidizing Agents. May react violently with air,

                           water, or other substances.

BLUE             Health Hazard.  Toxic if inhaled, ingested, or absorbed

                             through the skin.

WHITE           Corrosive.  May harm skin, eyes, or mucous membrane.

GREEN or     Presents no more than moderate hazard in any category.

ORANGE

 

On the separate page of your lab notebook you should copy a more detailed or specific hazard for each NFPA category as shown below:

 

Link to the following Government web site for more details:

http://www.sefsc.noaa.gov/HTMLdocs/nfpahazard.htm

This site has the following symbol

HEALTH - The degree of health hazard of a chemical or material is based on the form or condition of the material, as well as its inherent properties.  The degree of health hazard of a material should indicate the degree of personal protective equipment required for working safety with the material.

1 is for slightly hazardous (toxic) material which requires only minimal protection (for example, safety glasses and gloves) in addition to normal work clothing to work with safely.

2 is for moderately toxic or a hazardous or moderately toxic material which requires additional PPE or equipment (e.g. chemical goggles, lab/work smock, local ventilation) in addition to that required for less toxic material. Consult the MSDS for specific health hazard and proper PPE to use with this material.

3 or 4 is for highly to extremely toxic (deadly) materials (and any carcinogen, mutagen, or teratogen).  These materials will require specialized equipment (e.g. respirator or exhaust hood, full face shield, rubber apron, specialized glove, handling tongs, etc) beyond that required for moderately toxic material.  You must consult the MSDS and/or other safety information to determine the hazard (acute or chronic) and the proper PPE and engineering controls to safely use this material.

 

FLAMMABILITY or FIRE HAZARD - The flammability or fire hazards deal with the degree of susceptibility of the material to ignite and burn.  The form or condition of the materials, as well as their properties, affects the extent of the hazard.  Many hazardous materials such as acetone and gasoline, have a flash point (ignition temperature) far below freezing and will readily ignite with a spark if the vapor concentration is sufficient. 

1 is for materials with a flash point above 200ºF.

2 is for materials with a flash point below 200ºF but above 100ºF.

3 is for materials with a flash point below 100ºF but above 73ºF.

4 is for materials with a flash point below 73ºF.

 

REACTIVITY - The reactivity hazards deal with the potential of a material or chemical to release energy.  Some materials are capable of rapid energy release without any catalyst, while others can undergo violent eruptive or explosive reactions if they come in contact with water or other materials.  Generally this rating is used to indicate the potential to react if the material is heated, jarred, or shocked. 

1 indicates a material that may be reactive if heated and one that reacts with water.

2 indicates a material that may react violently without detonation.

3 indicates a material that may detonate or explode if subjected to a strong initiating force or heating under confinement.

 4 indicates a material that readily detonates or explodes.

 

SPECIFIC HAZARD - An open space at the bottom of the NFPA diagram can be used to indicate additional information about the chemical or material.  This information may include the chemical or material's radioactivity, proper fire extinguishing agent, skin hazard, its use in pressurized containers, protective equipment required, or unusual reactivity with water. 

 OX or OXY indicates a material that is an oxidizer.

 W or W indicates a material that is water reactive.

ALK indicates a material that is alkali.

COR indicates a material that is corrosive.

RAD indicates a material that is radioactive.

Special Labeling Requirements

All containers that hold carcinogens, reproductive hazards or acutely toxic chemicals must be properly labeled concerning the health hazard posed by the chemical.  Most containers will have the chemicals hazard clearly displayed on the label.  However older chemicals and containers of solutions that are mixed in the lab must be properly labeled by the laboratory worker.  The laboratory worker may write the hazard class (e.g. carcinogen, etc.) on the container or use labels available from their Supervisor or Chemical Hygiene Officer.

 

Lab Symbols You Must Know:

      

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The MSDS web site may be accessed at the following:

http://www.ilpi.com/msds/ref/nfpa.html

 

In your lab notebook sketch the following HMIS Labeling System and list the descriptions for each number:

 

Below is a paragraph about the two labeling systems:

 

“At first glance, the HMIS® and NFPA labeling systems appear quite similar. Both have four sections colored blue, red, yellow and white. HMIS® uses colored bars, while NFPA uses colored diamonds. HMIS® attempts to convey full health warning information to all employees while NFPA is meant primarily for fire fighters and other emergency responders.”

In your lab notebook, the purpose behind the both system and why they are different.

MSDS Relevance

Specific sections of an HMIS® label include the following:

Health

o                                The Health section conveys the health hazards of the material. In the latest version of HMIS®, the blue Health bar has two spaces, one for an asterisk and one for a numeric hazard rating.

If present, the asterisk signifies a chronic health hazard, meaning that long-term exposure to the material could cause a health problem such as emphysema or kidney damage. NFPA lacks this important information because the NFPA system is meant only for emergency or acute (short-term) exposures.

According to NPCA, the numeric hazard assessment procedure is different than that used by NFPA. Here are the numeric rankings for the HMIS system:

 4 

Life-threatening, major or permanent damage may result from single or repeated overexposures.

 3 

Major injury likely unless prompt action is taken and medical treatment is given.

 2 

Temporary or minor injury may occur.

 1 

Irritation or minor reversible injury possible.

 0 

No significant risk to health.

 

Flammability

For HMIS I and II, the criteria used to assign numeric values (0 = low hazard to 4 = high hazard) are identical to those used by NFPA. In other words, in this category, the systems are identical.

For HMIS III, the flammability criteria are defined according to OSHA standards:

 4 

Flammable gases, or very volatile flammable liquids with flash points below 73 °F, and boiling points below 100 F. Materials may ignite spontaneously with air. (Class IA) .

 3 

Materials capable of ignition under almost all normal temperature conditions. Includes flammable liquids with flash points below 73 °F and boiling points above 100 °F, as well as liquids with flash points between 73 °F and 100 °F. (Classes IB & IC).

 2 

Materials which must be moderately heated or exposed to high ambient temperatures before ignition will occur. Includes liquids having a flash point at or above 100 °F but below 200 °F. (Classes II & IIIA).

 1 

Materials that must be preheated before ignition will occur. Includes liquids, solids and semi solids having a flash point above 200 °F. (Class IIIB).

 0 

Materials that will not burn.

 

 

 

 

 

Reactivity (HMIS® I and II - now obsolete)

o                                The criteria used to assign numeric values (0 = low hazard to 4 = high hazard) were identical to those used by NFPA. In other words, in this category, the systems were identical.

This version is now obsolete. The yellow section has been replaced with an orange section titled Physical Hazards - see the next section for more information.

 

Physical Hazard (HMIS® III)

o                                Reactivity hazard are assessed using the OSHA criterion of physical hazard. Seven such hazard classes are recognized:

§                                 Water Reactives

§                                 Organic Peroxides

§                                 Explosives

§                                 Compressed gases

§                                 Pyrophoric materials.

§                                 Oxidizers

§                                 Unstable Reactives

This version replaces the now-obsolete yellow section titled Reactivity - see the previous section for more information. As with the Health and Flammability sections, the level of hazard is indicated using numeric values (0 = low hazard to 4 = high hazard):

 4 

Materials that are readily capable of explosive water reaction, detonation or explosive decomposition, polymerization, or self-reaction at normal temperature and pressure.

 3 

Materials that may form explosive mixtures with water and are capable of detonation or explosive reaction in the presence of a strong initiating source. Materials may polymerize, decompose, self-react, or undergo other chemical change at normal temperature and pressure with moderate risk of explosion.

 2 

Materials that are unstable and may undergo violent chemical changes at normal temperature and pressure with low risk for explosion. Materials may react violently with water or form peroxides upon exposure to air.

 1 

Materials that are normally stable but can become unstable (self-react) at high temperatures and pressures. Materials may react non-violently with water or undergo hazardous polymerization in the absence of inhibitors.

 0 

Materials that are normally stable, even under fire conditions, and will not react with water, polymerize, decompose , condense, or self-react. Non-explosives.

 

Personal Protection

o                                This is by far the largest area of difference between the NFPA and HMIS® systems. In the NFPA system, the white area is used to convey special hazards whereas HMIS® uses the white section to indicate what personal protective equipment (PPE) should be used when working with the material.

Note: The NPCA specifically recommends that "preparers of MSDSs should not place HMIS® PPE designation codes on the MSDSs or labels that leave the facility, as they do not know the conditions under which their customers use those products." However, these still turn up on some MSDS's.

HMIS® uses a letter coding system for this section. We at ILPI find this unacceptable because we would rather see the PPE listed explicitly instead of having employees try to remember a bunch of codes or consult a chart, something that could lead to confusion and/or a fatal accident. Likewise, the "custom codes" aspect is particularly dangerous for visitors and contractors who may not remember/recognize that these could vary from job site to job site.

Note: Some of the letters/symbols used in this table are also used as TSCA, CHIP, and/or DoD HMIRS/HCC codes, all of which have completely different meanings and applications! Say, did we tell you we dislike code systems?

We present the lettering scheme here, along with a series of graphics meant to reinforce the meaning of each letter:

HMIS® Letter

Required Equipment

A

Safety Glasses

B

Safety GlassesGloves

C

Safety GlassesGlovesApron

D

Full Face ShieldGlovesApron

E

Safety GlassesGlovesDust

F

Safety GlassesGlovesApronDust

G

Safety GlassesGlovesVapor

H

Safety GogglesGlovesApronVapor

I

Safety GlassesGlovesDustVapor

J

Safety GogglesGlovesApronDustVapor

K

Airline Hood or MaskGlovesFull protective suitBoots

L through Z

Site-specific label. Ask your supervisor or safety specialist for handling instructions

 

 

 

 

 

 

 

 

 

MSDS Laboratory Assignment 

(Please submit your form with this assignment Place numbers in label below.)

Student Name: _____________________________

 

Compound: ________________________________

 

Chemical Formula: _________________________

 

Appearance & Odor: ________________________

 

Boiling Point: _______    Melting Point: ________

 

Solubility in water: __________________________

 

Conditions to Avoid:_________________________

___________________________________________

 

Materials to Avoid: __________________________

 

 

Using Chemical Date Bases on the next page fill in the above form in your Lab Notebook and submit by the second lab period.

 

MSDS Laboratory Assignment

List of Compounds and Elements

 

1.      calcium chloride

2.      sodium sulfate

3.      barium chloride

4.      hydrochloric acid

5.      sulfuric acid

6.      nitric acid

7.      naphthalene

8.      sucrose

9.      potassium chloride

10.  silver nitrate

11.  sodium nitrate

12.  ethanol (ethyl alcohol)

13.  nickel sulfate (nickel II or nickleous sulfate)

14.  copper sulfate (copper II  or cupric sulfate)

15.  magnesium sulfate

16.  iodine

17.  magnesium

18.  magnesium oxide

19.  2-propanol (isopropanol or isopropyl alcohol)

20.  sodium hydroxide

21.  ammonia or ammonium hydroxide

22.  aluminum chloride

23.  magnesium chloride

24.  boric acid

25.  phosphoric acid

26.  ascorbic acid (Vitamin C)

27.  silicon dioxide (sand)

28.  camphor

29.  sodium bicarbonate

30.  sodium acetate

31.  methyl alcohol (methanol)

32.  formaldehyde (Methanal)

33.  Benzene

34.  acetic acid (Ethanoic acid)

 

Some chemical information sites to research your assigned chemical:

Oxford University: http://msds.chem.ox.ac.uk/#MSDS

Internet Resources for MSDS: http://www.ilpi.com/msds/index.html#What

University of Akron Date Base: http://ull.chemistry.uakron.edu/erd/

Otherwise apply a web search for MSDS and find your chemical’s data on the web.

MSDS Sample – Acetone on next page

 

 

 

Significant Figures in the Laboratory

by

Dr. David Summers, USAF Academy

 

Quantitative observations in chemistry laboratory work routinely include measurements of such quantities as masses, volumes, and temperatures.  Despite the apparent diversity of these measurements, they all share one general feature that’s important to notice.  They all involve the reading of a scale – the markings on a graduated cylinder, a meter stick, a beam balance, an optical scale, etc.  Many instruments in the modern laboratory have digital readouts.  You should not be lulled, however, into thinking that they are absolutely accurate, since somewhere, at some time, the digital scale was calibrated by a human being reading a scale.

 

The thermometer at the right will serve for our present discussion. 

 

Read this thermometer and write your reading down here: _________°C.  (Do it NOW!)

 

Without being able to peek over your shoulder, it’s hard to discuss your actual measurement, but a safe bet would be that your answer is “24-point-something.”  Assuming that the marks on the thermometer were correctly placed, we can say that the “2” and the “4” are known with total certainty.

 

However, more can be said about the temperature.  You would probably agree that the reading is not as high as 24.9 °C, and it is certainly higher than 24.0 °C, or something in this neighborhood.  Maybe the best answer would be 24.3 ± 0.1 °C, indicating the apparent doubt we have about how far the mercury is between 24 °C and 25 °C.  Our best guess for the number is 24.3, and the uncertainty is about ± 0.1.

 

Before continuing, an important definition:  We will say that the Celsius temperature is known to three significant figures.

The number of significant figures is found by looking at the position of the first digit in the uncertainty (the tenths position in this example) and then counting all the digits in the number (from the left) up to and including this position.

 

Sometimes significant figures are explained by saying that we count all the digits whose certainty is known (“2” and “4”) plus the first uncertain digit (the “3”).  This can be misleading, however, because if the reading is 24.9 ± 0.1, then the “ones” digit is not certain (it is “4” in 24.8 and 24.9, but it is “5” in 25.0), but the “best guess,” 24.9, still has three significant figures.

 

Chances are that you know your weight to three significant figures also.  “I weigh about 152 pounds” suggests that your actual weight might be 150-154 pounds or so.  The uncertainty is about ± 2, in the ones position.  The number 152 has 3 digits up to and including the ones position, or 3 significant figures.

 

If this is where things ended with significant figures, all that we would have is a definition to play with, but there is more –

 

 

 

General Assumptions Regarding Significant Figures

 

1.         Notice that the number of significant figures is determined by the person doing the measuring.  You need to decide the uncertainty in your scale readings.  Naturally, however, if the instrument is out of adjustment, there will be “built-in” error or uncertainty that you might not be aware of.  In some cases, this might reduce the number of significant figures you can claim to have, just as a badly-sighted rifle would reduce target practice scores.  In Chemistry, we assume “well-sighted rifles,” so the uncertainty is presumed to be something between you and the scale you are staring at.  This assumption is not always justified – in some cases, you may want to blame the instrument or procedure itself for errors you find.  Fine!  Just supply evidence and reasons!

 

2.         Notice that in everyday life, you tend to follow an unspoken, intuitive rule: 

Stop a numerical expression when you reach the position of the first digit of uncertainty.  A person says “I weigh about 155 pounds.”  He doesn’t say, “I weigh about 155.2386439 pounds.” You followed this intuitive rule with your thermometer reading by stopping at the tenths position.  All we ask is that you continue to follow this unspoken guideline in chemistry.  Stop a numerical expression when you reach (roughly speaking) the first uncertain digit.

 

3.         Notice, also, in everyday life people assume when they hear a numerical expression that the last digit is the only uncertain one.  If you are told that the road you are looking for is 4.6 miles ahead on the right, you would be a little upset to miss the turn, only to discover that it was 3.6 miles instead.  If the person had said “about four miles,” you might have started looking for the road earlier.  Since the tenths were expressed, you assumed that the “4” was known with certainty – just because that’s the way we intuitively operate.  Again, all we ask is for you to make the same assumption.  The first uncertain digit is the last one expressed.  If you say the magnesium ribbon is 18.46 centimeters long, we will take the “1” and “8” and “4” to be certain, but will assume the “6” is a little doubtful – therefore we declare there are “four significant figures.”

 

 

 

 

 

 

Multiplication and Division

 

Now, let’s look at what happens when we want to multiply or divide numerical measurements.  A student measures a rectangular piece of tile, and reports the measurements:  Length:  15.1 cm; Width:  3.2 cm.  What, then, is the area of the tile surface?

 

Here is the way one student worked the problem on a calculator:

 

Area = (Length) x (Width).  A = (15.1 cm) x (3.2 cm) = 48.32 cm2.

 

The student was quite happy with “48.32 square centimeters.” This answer, however, is not only incorrect, but downright dishonest!

 

Remember that the last digit reported is the uncertain one.  The honest length is 15.1 ± 0.1 cm, and the honest width is 3.2 ± 0.1 cm.  (The uncertainties might even be larger than this.)  The area of the tile could conceivably be (15.2 cm) x (3.3 cm) = 50.16 cm2.  At the other extreme, the area could be (15.0 cm) x (3.1 cm) = 46.5 cm2.

 

So what are we certain about in this answer?  The area could vary from over 46 to 50 cm2, simply due to the doubt that is always built into judging distance between scale markings.  The calculated number is 48.32 cm, but the uncertainty is about ± 1.8 cm.  Since the first position in the uncertainty is the ones position, that is where the value of the area should “stop,” therefore the correct answer must be “48 cm2.”  Everything after the doubtful 8 must be chopped off.  It is dishonest to report 48.32 cm2, simply because that would imply that the first uncertain digit is in the hundredths place.  You just don’t know anything approaching this much certainty about the number.  If you want higher precision, the only way to get it is to make more precise measurements.  Carrying out things to greater extremes on paper when you calculate is simply self-deception and a waste of time.

 

Another example:

                    7 sf               3 sf          3 sf    

(21.00000)   x   (3.00)   =   63.0          (NOT 63.00000!!)

 

The same rules holds true for division:

 

21.00000 / 3.00  =  7.00

 

(Our answer is limited to three significant figures by the 3.00.)  If you are multiplying and dividing together, things still work the same way:

 

[(2.000) x (4.1) x (10.0000000)] / 3.00000 = 27         (NOT 27.3333333!!)

 

Here we are limited by the two significant figures in 4.1!

 

 

Zeros as Significant Figures

We have been implying that the number 10.0 has three significant figures.  If the person went to the trouble of putting the zero after the decimal point, there must have been a reason for it; this just happens to be the first uncertain digit, we assume.  This is fine.  (Of course, many students just add zeros to add zeros, so we have to follow the rules so we know that 10.0 does indeed have three significant figures.)

 

How many significant figures are there in 10,000 yr?  If this represents the estimated time since the last Ice Age, it’s fairly clear that there are five significant figures here!  In other words, we are uncertain by more than ± 1 year – in fact, the uncertainty is probably more than hundreds of years, maybe even thousands of years.

 

How would you express 10,000 yr to indicate that this might be uncertain by, say, at least a few hundred years?  You can’t chop the last two zeros – they are needed to represent the size of the number.  This is the best way: 1.00 x 104 yr.  In scientific notation we simply leave those zeros that we wish; we are showing three significant figures in 1.00 x 104; 10,000 to two significant figures would be 1.0 x 104.

 

Now work this problem:  (10.0) x (10.0) = ???  Well, the answer should have three significant figures, and the answer is obviously “one hundred.”  But if you write 100, you are leaving the reader to wonder whether any of the zeros are significant. 

Solution:  1.00 x 102.

 

How many significant figures are there in 0.00033?  Before you think too far here, put the number in scientific notation: 3.3 x10-4.  Now how many significant figures are there?  Both expressions have two significant figures.  Apparently the only function of those left-hand zeros in 0.00033 is to keep the decimal point where it belongs. Zeros to the left of all other numbers are never significant; they are only place-holders.

 

To summarize, here are some examples of significant figure determinations:

 

4.00030

6 significant figures

0.00300

3 significant figures

1.02050

6 significant figures

10,000.0

6 significant figures

10,000

? significant figures (ambiguous; could be 1-5)

10.000

5 significant figures

 

If you fail to understand any of these examples, check with your instructor.

 

Rounding Off

 

If we wish to express the number 326.337 to four significant figures, we would write 326.3.  To make it have 3 significant figures, since the first nonsignificant figure is less than 5, we simply drop it.  How would you express the same number to two significant figures?  320?  330?  3.2 x 102?  3.3 x 102?  Here, the first nonsignificant figure we are dropping is greater than 5 – the number is closer to 330 than 320.  But “330” fails to tell us whether the zero is significant.  3.3 x 102 is the clearest answer.

 

Suppose we wish to express the number 37.52 to two significant figures.  Here the first nonsignificant figure being dropped is 5 and it is followed by a non-zero digit, 2.  Since the 2 is the second nonsignificant figure, it contributes nothing in helping us make our decision.  In fact, we treat 37.52 as though it were 37.50.  So, do you round up or round down?  Example:  Express 37.50 to two significant figures.  It is clear there is not really a best way of operating here, since 37.50 is just a close to 37 as it is to 38.  Many scientists decide in cases like this to round to the even digit.  This rule simply guarantees that over a large number of “round-offs” about half the time we would round up, and half the time round down.  Thus 38.5 to two significant figures would also be 38.  However, 39.5 would be rounded up to 40, so that the last digit of the number, the zero, is an even number.  Using this rule, you will never get an ODD number when you round off a number ending in 5.  It is expected that you will follow this rule for any rounding that you do.

 

Final Comments on Significant Figures

 

1.         Learn the rules – they save time – but remember that the only justification for all of this business is to avoid saying more about a calculated value than you can possibly know.  It should be admitted that “significant figures” are only a simple shortcut for indicating the uncertainty of numbers; if you pursue this topic further, you will discover cases where “significant figures” give you incorrect estimates of uncertainty.  This should not diminish their routine utility; as long as you think significant figures you will avoid gross misstatements of uncertainty (and save yourself a lot of lost points).  You should not have to ask “How far do I carry my answers out?”  Stop when you reach the first position of uncertainty.

 

2.         Textbook authors and problem writers routinely violate significant figure rules.  You will probably notice this more than once in this course.  Be assured that we fully intend to consistently follow our own advice, and we will expect you to do the same – particularly on laboratory calculations and on homework and tests.

 

3.         What is the “rule” for adding and subtracting numbers with significant figures?  Well, there really isn’t any, if you insist on referring to significant figures.  But, there is a simple way of knowing how to round off your addition and subtraction results:

 

 

  2.34000

=

  2.3

 

  0.001

=

  0.0

 

  4.3

=

  4.3

 

10.82

=

10.8

+

  3.37

=

  3.4

 

        ?

 

20.8

           

 

 

 

 

 

 

Round off each term to the first position of uncertainty in any number that contains an uncertain digit.  Then add.  (Or add the numbers first, and then round back to the least amount of decimal places in any numerical value that was included in the calculation.)  In either case, you have avoided extending things beyond the first uncertain digit.

 

4.         Please keep in mind that this entire discussion has been limited to numbers involved with scale-reading type measurements.  There are other kinds of numbers – particularly counting numbers or defined numbers – which can lead you astray if you blindly follow rules.

 

For example, there are exactly 12 in a dozen.  The number “12” has what amounts to an infinite number of significant figures: 12.00000000000……. and so on.

 

There are exactly 1000 milliliters in a liter, because we define it to be that way.

 

If you count 23 people in a room, that is assumed to be exactly 23.

 

These kinds of numbers can never limit the number of significant figures in any calculated result from multiplying or dividing.  Thus:  If I count exactly 144,000 nails, then that is 12,000 dozen nails, exactly, even though you might think that 144,000/12 should be carried out to only two significant figures.  Similarly, in converting 1.0612 liters to milliliters I would calculate (1.0612 L)(1000 mL/L) = 1061.2 mL  The number of significant figures (5) in the answer is limited by the number of significant figures in 1.0612 L, NOT by the number 1000, which in this example is an exact number.

 

Lab Instructor Comment:

Please review Chapter 2 in your Lecture 1025 textbook for the discussion of Significant Figures. See Chapter 1 in CHM 1032C. Dr Summers has an excellent handout and he has given us permission to use any of his handouts here at FSCJ.