[CHM 112] Gaseous Equilibrium Graph

[Andrew J. Pounds]

On 07/14/14 21:35,  wrote:
> Good evening,
> I am working on Lab 8.
> under the Equillibrium section for our 5 test tubes there is a section 
> for values of FeSCN2+, Fe3+, and SCN-. How do we compute the values 
> for those answers?
> Thank you for your time,
>
In the first part of the lab (when you built the Beer's law plot) all of 
the SCN- was converted to FeSCN2+ -- so the concentration of FeSCN2+ was 
equal to the initial concentration of SCN-.   This is not the case in 
the equilibrium section and we need some way to determine the 
equilibrium concentrations.

This is where your calibration curve comes in.   You measured the 
absorbance for each of the tubes in the equlibrium section of the lab.  
In each case you were measuring the absorbance of FeSCN2+ (just like you 
did in the first part).   In this second part, however, you don't 
initially know the concentrations of the FeSCN2+ at equilibrium -- but 
you can use the absorbance AND your calibration plot to determine it.

For each of your solutions in the equilibrium section, determine the 
concentration of FeSCN2+ at equilibrium by finding that corresponding 
concentration for the measured absorbance on your plot.   Write that down.

Remember, for each solution you are going to have to build an ice 
table.  As such, for each solution you have an initial Fe3+, SCN- and 
FeSCN2+ concentration (the last one will be zero each time). You also - 
based on your measured absorbance and interpolated concentration, know 
the EQUILIBRIUM CONCENTRATION OF FeSCN2+. Fill this out on your ICE 
table.   This will be the value of "x" in your ICE table.   Use this to 
determine the equilibrium concentrations of Fe3+ and SCN-.



-- 
Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
Professor of Chemistry and Computer Science
Mercer University,  Macon, GA 31207   (478) 301-5627
http://faculty.mercer.edu/pounds_aj

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