Questions and answers in Chem435
Here you can post your comments (anonymously if you wish) , questions and even get answers:
Previous semesters: SP 08,SP 07,
SP 06,
SP 05,
SP 04,
SP 03,
SP 02,
SP 01,
SP 00
Spring 20010:
Q11 (4/27/10): For the
1,4-benzosemiquinone experiment, here is what I wrote down: nu =
9.75 GHz, Center field = 3474 G, Sweep width = 15 G, modulation
amplitude = 0.3 (don't know the units), Receiver gain = 4 x 10^3
(don't know the units). I must be missing something here. Isn't
the field strength supposed to be in Tesla?
A11 (4/27/10): 10000 G = 1 Tesla.
Modulation amplitude (MA) is also in G, but it is not important
as long as you do not overmodulate the signal, i.e. D<MA.
Q10 (4/26/10): How do we find the
g value of Mn2+ by looking at the graph of the data?
A10 (4/26/10): g *b*H =h*n.
Thus, unless you have written down the frequency and the field,
you won't be able to. >As we hve discussed, it should be close
to g=2 .
Q9 (4/26/10): For the ESR lab
when finding the linewidth, say the distance between min and max
is 8G do i need to multiply that by 1.866 since "gamma is
(3^(1/2))/2 = 0.866 times greater than the linewidth measured
between maximum and minimum of the first derivative."
A9 (4/27/10): As it says after eq.(15) in the intro for
the lab and shown in the picture next to it, G =
0.866 D, where D is the distance
between minimum and maximum.
Q8 (3/24/10): Dr. Smirnov, I was
wondering what exactly you are looking for in the presentation?
Are we presenting it with results we got from it or just about
the experiment itself?
A8 (3/28/10): In your oral presentation you should decribe
what the lab was about, your results and discussion of what these
results mean. Treat it as if you were presenting a research
project at a conference. You will have 20 minutes to do that.
There are numerous suggestions online on how to make a good
presentation. I give some links (maybe outdated) on the resources page. The rule of thumb is - start with what you are
about to telll (i.e. an outline) the tell about it (i.e.
description of the experiment, results and discussion) and finish
by summarizing what was achieved (i.e. conclusion).
Q7 (3/06/10): Hi,professor:
The printout from Cary 100 thermal application software shows us
the Tm, delta H, and delta S already. So do we need to calculate
the Tm, delta H, and delta S values?
A7 (3/06/10): There are two ways for obtaining DH°, DS°,
and DG°:
- from the plot of 1/Tm vs DNA concentration and
- from the temperature dependence of the equilibrium constant
The latter is provided by the software for each trace (i.e. each
concentration) and, as you can see, varies in the experiments.
You will need to compare your value obtained from 1/Tm vs ln[C]
plot and (the average values) from the lnK vs 1/T plots (provided
by the software)
Q6 (2/27/10): Is "delta
gamma" the uncertainty in the table you want us to make?? We
did the sound velocity for natural gas.Can you give me some
advise for what and how to write about the natural gas?Do you
want us to compare with something?(I calculated the gamma for
natural gas)
A6 (2/27/10): Yes to the first question.
As for the second question, presume that it is a pure
hydrocarbon, not a mixture, and identify what it is by narrowing
down the possibilities and then identify the gamma. How does it
compare with the theoretical values?
Q5 (2/06/10): For experiment 2
when using DH = DE + RTDngas to determine DH, what T do we use?
final, initial or another one???
A5 (1/06/10): There should be minimal difference when
using either (~2 K over 300K). May be the final T is more
appropriate.
Q4 (1/27/10): I am interested to
know about the last question, the one regardign the generation of
a value for pi. In the Monte Carlo simulation, we are told that
N= different large values. Then we are given 10 runs for each of
these large numbers. When we calculate the mean, we are using
N=10 for the 10 runs, but then we calculate the Confidence
Interval with N=2000? I'm confused.
A4 (1/27/10): Analyze each set on itself and calculated
the mean and the error. AFTER THAT, discuss how the error changes
between the ten sets and correlate it with that N of Monte Carlo
simulation. Is there any correlation? Does it increase or
decrease with N? Extra: what dependence would you expect?
Q3 (1/25/10): I am doing the
fitting for the question #1 of the first assignment, so what is
initial intensity Io for the equation I = Ioexp(-t/t), is it also
a parameter?
A3 (1/25/10): Yes.
Q2 (1/24/10): I am confused by
the data in the kinetics.txt file. Are the values the measure of
intensity I or of some change in the previous intensity? If they
are a change in intensity, then what is the initial intensity?
Many of the values are negative so I cannot calculate the ln of
them. That's why I think I'm on the wrong track.
A2 (1/24/10): The file presents the intensity as a
function of time. Yes, there are points with negative intensity
as you would likely observe in the experiment. You should ignore
them. The intensity evolves from 'zero', befor the laser
excitation, then rizes upon excitation and gradually decays due
to luminescence process. I hope it answers your question. I have
copied your question and my answer on the Q&A page.
Q1 (1/24/10): For the propagation
of error question, here's what I have so far. R = (pV) / nT
Including uncertainties in the measurements of P, V, and T: R =
(p ᠰ.1%)(V ) --> R = 8.40 ᠳqrt( 0.12 + 12 + 0.52)%
--> R = 8.40 ౮12% ------------------------- R = 8.49 ᠰ.09
n (T ᠰ.5%) Including the systematic error in measuring T is
where I have trouble. *** We don't know the number of T
measurements that were made, but they were all too high by 1%.
That means that R is doing to be too low. How do we include this
in the final value of R? Thanks,
A1 (1/24/10): When you are not sure, always start with
definitions. You need to calculate the derivatives (dR/dV, dR/dP, dR/dT)
and express the systematic error as dR = ((dR/dV)dV+ (dR/dP)dP+ (dR/dT)dT)
and the random error as DR = {(dR/dV)2
DV2 + (dR/dP)2
DP2 + (dR/dT)2DT2}1/2
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Last updated on 04/27/10