exp 17 questions, sample calculations and sig. fig. for slopes, graphs. etc.

[Zellmer, Robert]

We're doing exp 17 this week.  Here's a few things which might help
with the report.

1) My on-line example is for the old exp.  You can still look at it to
    see what a zero-order plot should look like.  If you scroll down
    to the bottom you'll find what you might find for the first and second
    order plots might look like.  See item #6 below for more explanation
    and links.

2) Your initial concs. for each solution are different.  You need to do a
    dilution calc (M2*V2=M1*V1) to get the initial Dye conc., [Dye]o,
    for each solution at the moment of mixing.  The M1 is the conc. on
    the bottle.  The V1 are the volumes you were told to use in lab, they
    may be different than what was in the manual since we made some
    changes as we went through the week and you didn't have to have
    volumes which exactly matched those in the manual for the Dye and
    the water.  Use your recorded volumes from lab.  The V2 should be
    the total volume of Dye, H2O and bleach at the moment of mixing.
    This should be close to 40 mL.

3) The manual gives an idea of what the report sheet should look like
    and what the tables should look like.  Use the provided Excel template
    on Carmen to make your data tables and the report sheets.  Make sure
    you have the proper headings, units, s.f., etc.  Import your tables from
    Excel into the report.  Do NOT scan tables or graphs and include a scan.

    My suggestion is to use a different worksheet in Excel for the data for
    each solution for Part B data.  That means you'll have 4 worksheets in
    Excel, one for each solution and each table would be on a single page
    in the report.  I'm referring to the table at the bottom of page 129 of the
    report sheet in the manual pages on Carmen for Part B time, absorbance
    and conc. data.

    Make a worksheet for solution 1 (i.e. get everything set up correctly in
    this table, labels, units, s.f., equations) and then copy the worksheet for
    soln 1 to three other worksheets for solutions 2, 3 and 4.  Then all you
    have to do is change your times and absorbance values in the tables for
    solutions 2, 3 and 4.  If you do this before making your graphs the s.f.
    set in your tables should transfer over to the graphs. The graphs also need
    to have the correct s.f. and units.

    Since you'll have multiple s.f. for the Abs values (ranging from 1 to 3,
    mostly 2) just use 2 s.f. for the y-axis (conc. related data) you derive from
    the Abs using the Beer's law eqn.  Go ahead and use 3 s.f. for the slopes
    and rate constants.

    If you have any negative Abs readings you can't use that data.

4) Sample calculations:

    [Dye]o and [Bleach]o  (at the moment of mixing)
    Beer's law constant (slope calc.)
    [Dye]t
    ln [Dye]t
    1 / [Dye]t
    Rate constant from any slope (graph 3 or 4)
    Average of the rate constants
    Average deviation for rate constants

5) You are suppose to report the Average value of the rate constants and
    the average deviation of the rate constants.  See the link at the "Laboratory"
    link which discusses the treatment of numerical data (Appendix F in your
    manual),

  Treatment of Numerical Data (Error Analysis, sig. fig., graphing)<https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/App_F_1250_lab_manual.pdf>

6) Graphs

    A)  Beer's law graph

    This graph should have 6 data points (5 solutions and the origin (0,0))
    and be forced through the origin (an option when you do the trend
    line).  You will know if you didn't do this if your eqn. has an intercept
    that isn't equal to zero. The slope of this graph should be over 20,000.

    B) Zero-order graph

    I have an example of a good zero-order graph for the old exp 17.
    Your graph won't look exactly the same but should be similar.

     Zero-Order graph<https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/exp17/exp17_web_graph2_ex.pdf> - Examples of a good graph

    These examples are for the zero-order plot. This is actual data
    and graphs from a previous year that I cleaned up. You can use
    an exponential or parabola for the zero-order plot (which ever
    seems to give a better fit, usually exponential). Do NOT use a
    linear fit for the zero-order plot.

    Note two lines cross toward the end. They shouldn't cross. There
    was something wrong with the data toward the end of the run
    for one of the solutions. A zero order graph should eventually
    approach zero so the lines for all 4 solutions will likely converge
    toward the end of the lines.  If they cross well before near the end
    that's a problem. When this happens you will notice in graphs
    3 or 4 for the 1st and 2nd order graphs (which ever produces the
    most parallel lines) the slope for the line which crosses the others isn't
    as similar to the slopes for the other lines (not as closely parallel).
    In this case you should report all four rate constants on the report
    sheet but might consider not including the "bad" rate constant in
    your average. It depends on how different it is from the other three
    You should discuss this in the Discussion section of the report.

    C) 1st and 2nd order graphs

    For the first and second-order graphs (graphs 3 and 4) you should use
    LINEAR fits (trend lines) for both graphs.  Do NOT go back and fit either
    to something other than linear.  You are looking to see which graph has lines
    that are more closely parallel.  Generally speaking, if you have good data
    you will see a distinct difference between the two graphs.  Also, which ever
    graph has lines which are more closely parallel will often produce a better
    straight line fit to the points.

    See the following link for generally of what you might see for these graphs,

    Graphs 3 & 4<https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/exp17/exp17_web_graphs_3_4_exs.pdf> - Exs of what Graphs 3 & 4 might look like

    What you should see is one of these two graphs will give parallel lines and
    the other won't.  So if the first-order graph has parallel straight lines the 2nd
    order graph will have lines which clearly aren't parallel and the data clearly
    doesn't fit a linear trend line.  If the 2nd-order graph has parallel straight lines
    the 1st-order graph will have lines which clearly aren't parallel and the data
    clearly doesn't fit a linear trend line.  However, even though the data on one
    of the graphs clearly won't be linear leave the fits as linear (don't go back and
    fit them to a non-linear curve).

    D) Misc.

    For graph 3 (1st-order) the label for the x-axis will likely be at the
    top of the graph. You can move it to the bottom. You actually
    have to right-click on the Y-axis, choose "Format Axis" and then
    choose "Value (X) axis crosses at:" or "Horizontal axis crosses:"
    and set this to the minimum value on the Y-axis. It should move
    to the bottom of the graph.

    Set all the graphs to be printed in LANDSCAPE mode (normally the
    default for Excel). This gives better looking graphs.  Set margins to
    zero.

7) What if one of your solutions gives "bad" data?  How will you know?
    Lets say for your zero-order graph one of the lines crosses the other
    lines well before 4 minutes.  What should you do?  Do your zero-order
    graph twice, once with all four solutions and once with only the three
    good ones.  Then do the first and second-order graphs with only the
    three good ones.

8) Don't forget to discuss how you chose the order based on graphs 3 and 4.
    Also, discuss WHY one of the graphs should have lines which are parallel.
    Compare the rates for the four solutions and do they make sense. Don't
    forget your rate constants and the rate law.  Look at the "Points to Consider".

    Please remember, my Excel example is just that, an example of what
    to do and how to do it. It is not a complete example and it's for the older
    exp 17 (NOT the current exp).

  I hope this helps.


Dr. Zellmer
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