Anyone done this beer's law spectrophotometer lab?
A=abc -or-
absorbance = (extinction coeff)(cell thickness)(concentration)
i also know that using the same wavelength and cuvet means the a and b are thrown out.
does this just mean the absorbance = the concentration ??
the lab is based on finding the equilibrium constant Kc for the equation...
(Fe+3) + (SCN-) <----> (FeNCS+2)
the first section of the lab that we did established the standardization curve and the second part is all about trying to predict the concentration of the (FeNCS+2) at equilibrium by using our standardized curve from part 1.
i am completely stuck as to what part of the graph i am looking at and how it fits in with beer's law.
any help is graciously accepted. thanks.
Answer:
Absorbance is not equal to concentration.
concentration have to be determined by the formula
A=abc or e(epilson)bc'
depending on the unit of your concentration. if it is in mol/L use the 2nd formula. if it is in g/L, use the 1st formula.
after finding the concentration, use the equilibrium equation. to determine the equilibrium concentration.
= [products] / [reactants]
in this expt u are plotting Abs against concentration,so how can Abs =concentartion?
this is a calibration garph whereby a certain no. of standards are prepared and their absorbance are measured using the spectrometer. the graph is a linear graph passes through the origin,since there is no y-intercept in the equation A=abc
once the calibration is done, the unknown concentration can be determined by measuring the absorbance and from here,the unknown can be found by interpolation using the calibration graph plotted earlier on.
you use your standard curve to figure out the concentrations of unknowns. write out the equilibrium equation and plug in what you know and solve for what you don't.
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