INTRODUCTION TO "PRELAB"AND
"LOGGER PRO/GRAPHICAL ANALYSIS"
PURPOSE
Learn to use the computer programs PRELAB and LOGGER PRO (or
GRAPHICAL ANALYSIS), which will be used throughout CHEM 122/124.
in the few hours immediately before the lab.
Don't even think of coming to lab saying "I
couldn't get this done ...". The start of lab is a
busy time, and the instructor's first priority is with
the students who are prepared. There are no
make-ups because you could not get the
prelab assignment done.
ABOUT PRELAB
For every experiment in the 122/124 labs, a
computer
program
called PRELAB (or
WinPrelab.exe) generates and grades an
individualized prelab exercise. Upon successful
completion of the assignment, the computer
prints an authorization sheet (with individualized
authorization number), which serves as your
ticket into the lab for that experiment. Without
the authorization sheet, you may not be admitted
to the lab and consequently assigned a grade of
zero for that experiment OR, at least, you will
have a significant number of points deducted
from your score.
The prelabs are individualized. Everyone
gets basically the same questions, except with
different numbers.
Therefore, each student
must print out his/her own problem sets. You do
not need to enter your answers at the same
computer where you printed the problems. By
entering your student number, the computer will
know which numbers you were assigned. Some
prelabs will require the use of another program,
LOGGER PRO (or GRAPHICAL ANALYSIS),
discussed below.
GETTING HELP
A review of the chemistry background needed
for each experiment is contained in the
introduction to that experiment. Also, the lab is
coordinated with the material presented in
lecture.
Therefore, the answers to your
chemistry questions can almost always be found
by going back to the books. Additionally, there is
a modest coursepack section after this handout
providing hints for successfully completing a few
of the prelab assignments.
If you are still unable to solve your problem,
you can get help from a tutor or one of your
instructors. They will get you pointed in the right
direction, but don't ask them to work your
problems for you. The teacher who simply gives
you answers, rather than leading you to think-itthrough for yourself, is not your friend.
At times it is productive to work with other
students. This is okay, but don't let anyone do
your work for you. It will be painfully obvious to
everyone at the end of the lab period, when you
are unable to finish the data analysis by yourself
and are asking for help, that your authorization
sheet was obtained under false pretenses.
TIME MANAGEMENT
The importance of starting early (days early) on
the prelab exercises cannot be overemphasized.
It is unlikely that all of your answers will be
correct the first time. Tutors, instructors and
computers may not be available for helping you
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Introduction to PRELAB and GRAPHICAL ANALYSIS
SIGNIFICANT FIGURES AND ROUNDING-OFF
UNITS AND EXPONENTIAL NOTATION
Now is the time to learn significant figures, for
once and for all! The computer knows them and
follows them meticulously (with one minor
exception discussed below).
To allow the computer to check each step of
your work, we made a modest compromise.
Normally, to minimize the accumulation of
"rounding errors," all figures would be carried
through until the end of a calculation sequence,
and then the final answer is rounded to the
proper significant figures. However, for the
prelabs, it is also acceptable to round each
answer to the proper significant figures for that
step, before using it in subsequent steps.
Be sure to round correctly. If the last digit
you are eliminating is exactly 5, the most
rigorous rule says you should round the
previous digit to the even number. Examples
(all rounding to 3 significant figures): 3.675 =
3.68, 3.685 = 3.68, 3.68501 = 3.69 (the 01
following the 5 indicates that the part you are
rounding-away is slightly greater than 5). The
common rule is to always round up if it's
exactly 5 (3.685 would round to 3.69).
There are two computer quirks you should be
aware of: (1) The computer uses the more
rigorous rule for rounding, but because
computers use base-2 rather than base-10,
occasionally, when the digit being rounded-away
is exactly 5, it may be rounded incorrectly. The
computer should give you a message if it thinks
you rounded incorrectly. (2) To a computer, a
zero at the end of a number (after the decimal
point) is equivalent to a blank space. Thus, if
your answer ends with a zero, the computer will
let you be sloppy about significant figures. For
example, if the expected answer is 1.40 (3 sig.
figs.), the computer will accept 1.4, 1.40, 1.400,
1.4000, ... as correct. However, if you use that
value in a subsequent calculation, the computer
will expect you to know that there were 3
significant figures (regardless of the number of
zeroes you entered).
Answers must be calculated using the units
requested by the computer. For example, if you
enter the correct number of grams, but the
program asks for kilograms, you will be told your
answer is incorrect. However, do NOT enter the
units when entering answers; the computer is
looking for numbers only.
Most answers do not need to be expressed in
exponential (scientific) notation, but you may if
you wish. To enter a number in exponential
notation, type the number, followed by the letter
e (or E) and then the exponent. Examples: 12.1
= 1.21e1, 1539.7 = 1.5397e3, 0.00012 = 1.2e4, 4310 = 4.31e3.
ABOUT LOGGER PRO
(and GRAPHICAL ANALYSIS)
Many experiments require repetitive calculations,
graphing, and statistical analysis. LOGGER
PRO is a friendly program that makes these
chores almost fun. It is very easy to use to
generate graphs. It is also like a spreadsheet in
that it operates on entire columns of numbers,
rather than individual numbers.
GRAPHICAL ANALYSIS is very similar to
LOGGER PRO. The major difference is that
LOGGER PRO is used in the lab for computerbased data acquisition and is updated more
frequently. GRAPHICAL ANALYSIS cannot be
used to collect data and it can only be entered
manually. However, once the data is in the
programs, the programs and commands used
are virtually identical.
WHERE TO FIND THE COMPUTERS
PRELAB and GRAPHICAL ANALYSIS are
available at any of the of the campus ICT labs
(270 Student Center, 101 Owen, the MultiMedia
Commons and Computing Commons in Halle
library, …). Our site license for LOGGER PRO
does not extend to these labs. It would be wise
to write down the hours that these facilities are
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Introduction to PRELAB and GRAPHICAL ANALYSIS
open. The typical hours are listed at the end of
this document.
The program can be accessed by clicking on
“Start” then choosing “Course Reserve Software”
and then Clicking on the appropriate program
name (Chem Prelab or Graphical Analysis).
Check the title screen to make sure you are
using the most recent version of the program
since some prelab assignments are changed
each year.
The departmental site license for both
LOGGER PRO and GRAPHICAL ANALYSIS
allows each student to use it on his/her home
computer. You can copy the folder containing
Graphical Analysis in the General Chemistry lab
onto a thumb drive. Be sure to copy the actual
folder containing Graphical Analysis (which
should be on the desktop, if not, then click on My
Computer and then select Local Disk (C:) Program Files – Vernier Software). [Don’t just
copy the useless shortcut icon from the desktop
in the chemistry lab.] In a pinch, a 30-day trial
version can be downloaded from vernier.com,
the software publisher.
The site license for LOGGER PRO allows
you to download it from the Vernier website.
Information on how to do this should be available
from your lab instructor.
The PRELAB program (called Prelab.exe or
Chem Prelab) can be copied directly off the
Desktop in the chemistry lab. This program can
also be directly downloaded from the EMU
Chemistry Department website, by going to
www.emich.edu/chemistry/students/download.
You may also need to download WinZip
(available at the Chemistry site) if you do not
have it.
Prelab will run using any version of Windows
after (and including) Windows95.
However,
both GRAPHICAL ANALYSIS and PRELAB only
work with PCs, not MACs. You can download
LOGGER PRO for either PCs or MACs.
PRELAB uses these to
individualized questions and
answers.
create
check
your
your
2. Click on the proper course number.
3. Obtain a printed copy of the Prelab
exercise you wish to work on.
The first time you use PRELAB you may wish
to obtain printouts of all of the assignments for
the semester. There is a specific button on the
screen for this.
To obtain the printout for a single experiment,
click on the experiment name and then choose
to print the questions for that experiment.
4. Work your assigned problems.
GRAPHICAL ANALYSIS, if appropriate.
Use
5. (If necessary) Restart PRELAB, and select
the experiment for which you have
completed the problems.
Re-enter your name and the last three digits
of your student number. The student number
must be re-entered exactly as it appears on the
printed questions.
6. Choose to enter your answers.
7. Enter your answers when prompted, until
all questions have been answered correctly.
You will be prompted for the answer to each
question, and immediately told if your answer is
correct. If an answer is incorrect, and that
answer is needed in subsequent problems, you
will not be prompted for the subsequent answers
because it would be impossible for them to be
correct. If necessary, stop working in PRELAB,
restart GRAPHICAL ANALYSIS, and redo the
calculations. [It is convenient to keep both
programs open and switch back and forth
between windows, as desired.] There is no
partial credit for getting some of the problems
correct, you must repeat until you get them all
correct. There is no penalty for repeating the
problems.
GETTING STARTED WITH PRELAB
1. Enter your name and last three digits of
your student number, when prompted.
8. Print out your authorization sheet.
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Introduction to PRELAB and GRAPHICAL ANALYSIS
exponential notation or regular numbers so it is
not necessary to convert).
9. Exit the program and depart in peace.
g. You have not calculated the answer
correctly with your calculator.
Calculator
errors are fairly common. Be sure to double
check that you are entering the correct numbers
into your calculator (read them off the original
problem sheet - occasionally they are copied
incorrectly).
What if PRELAB won't accept my answer, but
I'm sure I did the problem correctly?
This does happen and it can lead to
considerable frustration. 99% of the time (at
least) the problem is one of the following:
a. Your student number is not the same on
BOTH the sheet with the questions AND the
screen when you input answers.
GETTING STARTED WITH LOGGER
PRO or GRAPHICAL ANALYSIS
Below are instructions for performing some of
the most common tasks you will need to perform
using either program. As with most computer
programs, often the best way to find things out is
to try something and see what happens.
b. You think you are answering a different
question than the one PRELAB is asking
about. Usually, PRELAB will make you answer
question 1 correctly before proceeding to
question 2. However, in some experiments the
answers to later questions do not depend upon
the first questions. If so, it may continue to the
next question even after receiving an incorrect
answer.
ENTERING DATA
There are two columns for data entry. After
typing a value and hitting the enter key, the
cursor moves to the next column in the same
row (or, from the last column, to the first column
of the next row). Hitting the down arrow key
(instead of the enter key) can be convenient for
entering a single column of numbers.
c. You are not using the current version of
PRELAB. A new version is issued about once a
year, a few questions and answers are not the
same as in previous versions. Therefore, you
cannot use an old disk or problem sheet. (The
current semester should appear on the title
screen of the program and on the problem sheet
you printed out - next to the experiment name.)
To change a column heading: double click
the mouse on the current column heading (X
and Y are the default headings). This will open
up a menu. (Note: to move between boxes you
can either click the mouse in the box to which
you are moving OR use the Tab key. If you hit
the Enter key, this is the same as clicking on the
OK button and will close the box.)
While in this menu, you can also change the
number of significant figures or places after the
decimal that are displayed. This capability is
found under the Options tab.
d. You do not have the correct number of
significant figures. The computer program
uses the rules given in chapter one of your
textbook. You should receive a message if your
answer is within one significant figure
e. You have not rounded correctly. You
should receive a message if this is the problem.
f. You are not entering the answer correctly
(typographical errors or units). Never enter
any units into PRELAB. It will convert them into
a number and tell you your answer is incorrect.
Often mistakes are made converting to and from
exponential notation (the program accepts either
To create a new column for data input
from the keyboard:
select Data  New
Manual Column from the menus. Then enter
the appropriate information in the boxes.
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Introduction to PRELAB and GRAPHICAL ANALYSIS
To create a new column of calculated
values:
select Data  New Calculated
Column from the menus. Next enter the name,
units, and formula in the appropriate boxes.
To enter an equation: The equation can be
entered by either typing in it in OR by using the
mouse to select the appropriate functions and
columns from the menus provided. The latter is
especially useful for selecting columns (since it
is quicker and eliminates typographical errors).
To enter the name of a column into an equation:
click on the Variables (Columns) box and then
click on the name of the column you are
inserting into the equation.
Once you have created a new column, in
order to it, you can either expand the data table
or click on the scroll bar at the bottom of the data
table window. If you made an error entering the
formula, double click on the column heading and
then edit the formula as desired.
clicking anywhere on the graph you can open up
the Graph Options window.
All graphs should have a title (or a caption).
The most appropriate title is simply: whateveris-plotted-on-the-y-axis vs. whatever-is-plottedon-the-x-axis.
By default, the program should autoscale the
graph. If you do not like the scaling it chooses,
you can alter it by clicking on the Axes Options
tab and choose to scale as you see fit.
“Autoscale Larger” is usually a poor choice.
Finally, make sure that each axis is properly
labeled (including units)! You can also change
axis labels and other graph features using the
choices in the Graph Options window.
4. Perform linear regression, if desired.
A. Select the points to be used.
By default, all of the points will be used, which
is ordinarily what you want. However, a smaller
range can be selected. This is done by moving
the mouse, on the graph itself, to the desired
data point on one end of the graph. Then click
and drag to move the mouse to the other end of
the desired points on the graph. (Selected
points appear with dark backgrounds on the
graph and in the data columns on the screen.)
B. Perform linear regression.
Now click on the linear regression button at the
top of the screen. This button has a curve on it
with a line going through it and the partial
equation “R=”.
A box should now appear on the graph with a
best-fit line through the points and a line
connecting the box to the best-fit line. This box
can be moved by a click-and-drag maneuver.
The box and best-fit line can be removed by
clicking on the little gray square in the upper
corner of the box.
Sometimes the text in the box is too small to
read clearly on the screen. This can be fixed by
double-clicking somewhere in the box, which
opens a table of options. (You may need to also
click on Appearance…) and change the font
size to something larger.
GENERATING GRAPHS
1. The data needs to be entered into two
columns. The column headings become the
axis labels when the graph is generated. These
can be changed as described above.
2. Choose which columns to graph. If you
only have two columns of data, these two
columns will automatically be graphed. If you
have more than two columns, the first column is
the default choice for the x-axis and the second
column is the default choice for the y-axis.
If you wish to change what columns are
graphed, use the mouse to click on the axis label
of the displayed graph in the Graph Window.
You will then be given the option of what
column(s) to graph.
Only one column can be chosen for the xaxis, but you can choose multiple y columns. If
you only want more than one column graphed on
the y-axis you may need to click on More... and
then turn on the desired columns by clicking on
them (to add the checkmark).
3. Fine tune the graph’s appearance
(title/connecting lines/scaling).
By double
5. Print the graph. Click on the File menu and
select Print Graph. Click on OK and the graph
will begin printing.
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Introduction to PRELAB and GRAPHICAL ANALYSIS
TYPICAL EMU LIBRARY
COMPUTING COMMONS HOURS
TYPICAL EMU LIBRARY
MULTIMEDIA COMMONS HOURS
Fall/Winter:
Mon-Thurs
Fri
Sat
Sun
Fall/Winter:
7:30am – 11:45 pm
7:30am - 7:45pm
9:00am - 5:45pm
12:00pm – 11:45am
Mon-Thurs
Fri
Sat
Sun
Spring/Summer
Mon-Thurs
Fri
Sat
Sun
7:30am – 11:45 pm
7:30am - 7:45pm
9:00am - 5:45pm
12:00pm – 11:45pm
Spring/Summer
7:30am - 9:45pm
7:30am - 4:45pm
9:00am - 4:45pm
1:00pm - 9:45pm
Mon-Thurs
Fri
Sat
Sun
7:30am - 9:45pm
7:30am - 4:45pm
9:00am - 4:45pm
1:00pm - 9:45pm
Intersession and Holiday hours as posted at the
library.
Intersession and Holiday hours as posted at the
library.
270 STUDENT CENTER
COMPUTING LAB HOURS
101 OWENS
COMPUTING LAB HOURS
Fall/Winter:
Mon-Thurs
Fri
Sat
Sun
Fall/Winter:
Open 24 Hours a day
Open 24 Hours a day
Open 24 Hours a day
Open 24 Hours a day
Mon-Thurs
Fri
Sat
Sun
Spring/Summer
Mon-Thurs
Fri
Sat
Sun
8:00am – 7:50 pm
Closed
Closed
Closed
Spring/Summer
7:00am - 8:50pm
7:00am - 8:50pm
8:00am - 8:50pm
Closed
Mon-Thurs
Fri
Sat
Sun
Intersession and Holiday hours as posted.
8:00am - 7:50pm
Closed
Closed
Closed
Intersession and Holiday hours as posted.
Current lab hours for all I.T. computer labs
should be posted at
http://www.emich.edu/it/help/labs/
xvi