Lab 4
o Computer Etiquette
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Calibrations and Calibration Curves
MicroLab Probe Calibration
MicroLab Data Analysis
Significant Figures and Graphing
Data for your In-class Assignment
Slope and Y-intercept – Significant Figures
What you need to turn in today
Next Assignment
In-class Assignment
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Do not surf the web
Do not check your e-mail unless it’s related to this course
Do not print materials unrelated to lab
Do not connect a USB mass storage drive
No social networking!!!
Do not open any attachments, unless directly from your lab
Blackboard shell or lab instructor e-mail.
You may access Blackboard from your lab computer once
given permission.
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Two types:
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Standard curves – to determine an instrument’s response to a
given analyte under a specific set of parameters (you worked with
two of these in your homework assignment)
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Internal calibration curves – to convert between a probe /
instrument’s native input and our required output (you will be
making up one of these today)
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pH probes require calibration in order to convert between their native input
(unit measured by the instrument, mV) and our required output (unit we are
required to measure or report, pH). This type of calibration is referred to as an
internal calibration.
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Your instructor will now show you how to calibrate a MicroLab pH probe after
which you will have an opportunity to practice.
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You can follow along with the instructions on p. 140 in your lab manual.
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Make sure your interface is turned on BEFORE you access MicroLab on the
computer.
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After you have finished your pH probe calibration and printed your graph,
exit out of MicroLab.
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Use your printed calibration curve to answer the “MicroLab™ Calibration
Exercise” questions on your report sheet on p. 147.
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Most of the data you work with in this lab will have a
linear curve fit.
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Once you determine the equation for the line, the
significant figures of the slope and the digits of
precision of the y-intercept need to be determined.
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We limit these values when we copy down the
equation, or when we use the values for the slope and
y-intercept in an equation.
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When determining the significant figures / digits of
precision to use for your equation, look only at the
non-zero data points in your data table.
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Your y-intercept is limited to the same digits of
precision as the values plotted on your y-axis.
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Your slope is limited to the same number of
significant figures as your data point with the fewest
number of significant figures.
Conductivity, S/cm
Potential Difference, V
0.0
0.00
720.0
0.18
1390.0
0.32
3300.0
0.73
6130.0
1.33
8400.0
1.82
When you plot the data from the previous table, you find that
the resulting graph has a linear curve fit. For the resulting
equation:
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How many significant figures should the slope have?
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How many digits of precision should your y-intercept have?
Remember this concept when you complete your in-class
assignment today!
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After you are finished today:
Make sure all questions have been answered.
 Submit today:
 Lab 4 report along with:
• pH probe calibration curve
• Spreadsheet for your in-class assignment
• Graph for your in-class assignment
 Make sure your name and section number are on the front page.
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Read the required reading sections in your textbook
and lab manual.
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Complete and submit the pre-lab questions by the
deadline.
 Question 4 will need to be completed in MicroLab™ in
the SCICom lab, Chemistry Resource Center or on your
computer if you downloaded the program. Plan
accordingly.
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Study for the quiz.
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See the “In-class” Presentation.