Explain Beer\'s law in words and with an equation. Include the basic assumptions

Question

Explain Beer's law in words and with an equation. Include the basic assumptions in the derivation of the formula. Describe the limitations of Beer's law i.e when does it fail/sources of error? Describe strategies for minimizing each source of error. Describe the function of each of the major components of a spectrometer? Light source, wavelength selector, sample holder, detectors) Include the advantages and disadvantages of the different options for each component. What are the types of noise that are commonly encountered in spectroscopic measurements? Describe strategies for minimizing each.

Explanation / Answer

Beer,s Law: When a beam of the monocromatic light passes through the solution then equal fraction of the insident light is absorbed by successive layer having equal concentration of the absorbing medium.

Mathematically , it can be stated as Absorbance = 2.303 log10 I0/ I := K 2..c

   Where Io= Intensity of the light insident on the layer

   I = intensity of the insident light on the layer

c = Concentration of the solution in moles

K2 = is the constant

Limitations of Beer,s Law: i)It is applicable to the dilute solution , it fails for highly conentratied solutions.To minimize the error the solution must be prepared in a solvent which will give a clear solution & should not form terbidity.Linearity of Absorbance 7 concentration is not observed above 1x10 -2M conc.

2)Law is not obeyed if absorbing species reacts with solvent

3)The insident light must be monocromatic

4)Temperature variation 7 entry of the light into the absorbing system lead to deviation&

Components of spectrophotometer:

1)Light source: is an incandescent lamp with a tungsten filament

2)Wavelength Selector: Color filter which selects a narrow band of wavelength

3)Sample holder: it is cuvette a rectangular transparent conainer made up of quartz or glass

4)Detector: A Photocell which converts the transmitted beam emerging from the sample into an electric current.

It is connected with dial on which the absorbance ie read directly.

Noise: is due to the chang in the intensity of te light due to voltage fluations in the power supply, hence use of stabilizer is expected

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