Lab 4
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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 created two
of these in your pre-lab 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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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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Follow the instructions starting on page 134 to create
your own hand-entry spreadsheet and graph.
Perform a calibration analysis.
The data to use will be introduced shortly.
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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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You will now be shown how to calibrate a MicroLab pH probe
after which you will have an opportunity to practice.
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Follow the instructions starting on page 135 to calibrate your
pH probe.
Perform a calibration analysis.
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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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Submit your Lab 4 Report
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Study for the next quiz.