density of acetonitrile as a function of temperature

[xyzzyx]

Hi all,
I was wondering if anyone in the chemistry community could point me in the
right direction of some data regarding the temperature dependence of the density
of acetonitrile (methylcyanide).

I am attempting to determine the extinction coefficient of a chemical in
acetonitrile. It occurred to me that it is essentially impossible to actually do this if
the concentration is not accurately known (A=epsilon * c * l or epsilon=A/(c*l)).
The best way to prepare an accurate solution would be on a molal
(weight/weight) basis, thus I'd always get it right, regardless of the temperature at
the time of preparation (as opposed to a molar (weight/volume) solution prepared
in a volumetric flask). The catch is that absorbance depends on pathlength (which
I can fix) and concentration (which will vary with temperature, as the solvent
changes density).

The obvious fix is to prepare a molar solution at a fixed temperature (assuming
that the vol flask can be accurately calibrated AT THAT TEMPERATURE) and collect
the spectral data AT THE SAME TEMPERATURE (sounds great in principle, but if
you think about it, it's actually pretty hard to carry out).

So the best I can think of is to make up a molal basis solution, measure the
temperature of the solution, accurately (after carefully equilibrating the cuvette to
the same temperature), measure the absorbance, and correct for the density of the
solution to get the concentration right.

I'd guess that the density/temperature data for acetonitrile must be in some chem
E. handbook somewhere (like the CRC has for water), but I haven't a clue as to
which one. If someone knows of a source for this data, I'd sure appreciate hearing
about it.

Any comments?

Thanks in advance for your time.

-George

[Ben Walker]

Try:

Kmol/m^3 = 1.3064/(.22597^(1+(1-T/545.5)^.28678))

=19.56 @ 273 K. T is in K above. Hope this helps.

Ben

[Uncle Al Schwartz]

You could thermostat your UV cell holder and dispense with all the woolgathering.
Temperature control +/- 0.1 C is trivial with a recirculating bath. I imagine
there are even solid state Pelletier temp controllers.

For acetonitrile
d=0.7822 g/ml 20 C
d=0.7766 g/ml 25 C Burdick & Jackson "Solvent Guide"

--
Alan "Uncle Al" Schwartz
Uncl...@ix.netcom.com ("zero" before @)
unc...@uvic.ca (summer only, cAsE-sensitive!)
http://www.ultra.net.au/~wisby/uncleal.htm
(Toxic URL! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?" The Net!

[Steven Arnold]

If you need it to be this accurate, you may also want to correct for the
refractive index of the acetonitrile solution. That is, the observed
absorbance depends upon the refractive index of the solution. The
observed absorbance A(obs) is given by:
A(obs) = A(true) n/( n^2 + 2 )^2 in which n is the refractive index
of the solution.

Steven Arnold
Assistant Professor of Chemistry
Oakland City University
Oakland City, IN

[jos]

xyzzyx <xyz...@wco.com> schreef in artikel <5n2qpg$pmg$1...@news.wco.com>...

I do not know if this will help you for sure, but it might.

In our line of work, we use density correction data to calculate the exact
amount of chemical cargoes on ship's. This is, measured volumes are
converted to kilo's at actual (measured) temperatures. To do this, we use
the so-called Density Correction Coefficient. This coefficient is derived
from the correlation curve between measured densities and test
temperatures. To determine this coefficient, we make the assumpion that
this curve is linear.
This is the point at where I do not know for sure if this coefficient is of
any use to you considering accuracy, because the curve isn't exactly
linear. To the 4th decimal however, errors in calculated densities are
neglectable.

Here's your data:

Test temp (°C) . observed density in vacuum (kg /l)

5 0.8231
15 0.8123
20 0.8068
35 0.7902

Density Correction Coefficient: - 0.00110 kg / liter .°C

Conversion of density in vacuum to air: - 0.0011 kg/l (valid only in the
specified temp. range)

Determination of above-stated data was performed in our own laboratory, so
there are no other sources I can state. For validation, you can contact me
per Email: jo...@pi.net

Regards,

Jos.

[Mark Tarka]

In article <01bc7596$26831400$0101dd91@p120jvv>, "jos" <jo...@pi.net> writes:
>xyzzyx <xyz...@wco.com> schreef in artikel <5n2qpg$pmg$1...@news.wco.com>...
>> Hi all,
>> I was wondering if anyone in the chemistry community could point me

[Snip...]

>In our line of work, we use density correction data to calculate the exact
>amount of chemical cargoes on ship's. This is, measured volumes are

[Snip...]

>Determination of above-stated data was performed in our own laboratory, so
>there are no other sources I can state. For validation, you can contact me
>per Email: jo...@pi.net

Er..._International_Critical_Tables_, seven or so volumes with an
issue published around 1929 or so, available at most if not all
major university libraries?

Mark gmt...@msu.oscs.montana.edu msu-bozeman USA