post lab discussion: exp. 10 Flashcards
it deals with the production, measurement and interpretation of spectra arising from the interaction of electromagnetic radiation with matter
spectroscopy
spectroscopy utilizing radiation in the UV-Vis range
UV-Vis Spectroscopy
what is the range wavelength of electromagnetic radiation in the UV–Vis portion of the spectrum
200 to 700 nm
UV range -
Vis range -
UV range - 200 to 350 nm
Vis range - 350nm to 700 nm
true or false:
the UV range is colorless to the human eye
true
true or false:
different wavelengths in the visible range does not have a characteristic color
false - they each have a characteristic color
what are the 2 general categories based on the type of radiation-matter interaction that the UV-Vis spectroscopy is divided to
absorbance
fluorescence
it is to determine the concentration analyte in a given solution
quantitative absorption spectroscopy
wavelength color:
less than 380 -
more than 780 -
less than 380 - ultraviolet (violet)
more than 780 - near infrared (purple)
the wheel color
R
O
Y
G
B
V
it is fast, simple and inexpensive method to determine the concentration of an analyte in solution, where the type of compound to be analyzed (‘analyte’) is known
UV-Vis analysis
what equipment can we use to analyze with UV-Vis analysis?
spectrophotometer
I0 =
I =
I0 = radiation coming in,
I = radiation coming out
decrease of a beam of radiation as it passes through a cuvette containing an absorbing solution
briefly explain what happens in the spectrophotometer machine
sample-holding cell or cuvette containing the solution to be analyzed is placed in the path of radiation of a selected wavelength
amount of radiation passing through the sample is measured relative to a reference sample
relative amount of light passing through the sample is then used to determine the concentration of the analyte (the substance being measured) in the solution
decrease in radiation intensity after passing through the solution is due to the absorption of photons by the absorbing species present in the solution
explain the difference between transmittance and absorbance
transmittance - fraction of the
incident light absorbed by the solution, defined as the ratio of I to I0.
T = I/I0
it can also be expressed as percentage: %T = (I/I0) × 100
absorbance - measure of the amount of light absorbed.
A = log(I0/I) = − logT = 2− log %T
according to ______ the absorbance is proportional to the concentration of the substance in solution
Beer’s Law
A = εcl
c = concentration of solution (M)
l = optical path length, i.e. dimension of the cuvette (cm)
e = molar absorptivity (L/mol·cm), which is constant for a particular substance at a particular wavelength; ↑ ε, ↑ amt. of radiation absorbed
it is the peak that represents the wavelength of maximum absorption
“lambda-max” (λmax)
the linearity of the Beer-Lambert law is limited by
chemical and instrumental factors
what are the 2 key advantages of taking measurements at this lambda-max peak
maximum sensitivity:
absorbance per unit change in analyte concentration, meaning measurements at the peak are most sensitive to concentration changes
greater adherence to beer’s law:
peak wavelength region, the radiation beam consists of wavelengths with relatively small differences in their molar absorptivities for the analyte being measured
when drawing calibration curve,
y axis:
x axis:
it is to determine?
y axis: absorbance
x axis: concentrations
determine the concentration of unknown sample solution by measuring its absorbance
what happens when the salicylate ions can be derived with Fe (III)
produce a violet colored complex
that can be quantified at its absorption maxima of 530nm
