Background Spectrophotometry #1: Analysis of Dyes Using Beer's Law In this experiment, clear dye solutions of different colors will be examined. Many...
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Spectrophotometry #1: Analysis of Dyes Using Beer's Law
In this experiment, clear dye solutions of different colors will be examined. Many chemical
solutions appear to be colorless. For example, saltwater (NaCl in water) is a clear, colorless
solution and food-coloring in water is a clear, colored solution. In this context, "clear" refers to
the fact that light can pass through.
When light shines on molecules or ions in these
solutions, light energy of various wavelengths
visible spectrum
absorbed by the species may result in electron
green blue
e violet
transitions. For solutions of a given color, the
energy of these transitions corresponds to
wavelengths of light in the visible region of the
Wavelength, nm
electromagnetic spectrum. Light may also be transmitted
through the solution unaffected or refracted (bent). We will
focus here on only the absorption of light by molecules in a
sample as this property gives rise to useful quantitati
both biological and chemical solutions.
Yellow -
It is possible that a species will interact with only light
outside of the visible region of the spectrum. In this case, no
color will be observed as the human eye is only sensitive to
the visible region of the spectrum. If there is only one
absorption region inside the visible spectrum then the color
observed will be the color across from the color absorbed
on a color wheel (at right). For instance, if light of ~630 nm
(orange) is primarily absorbed, then the observed color will
Figure 1. Visible light spectrum wavelengths
be blue; blue is the complementary color of orange. If there
(top); color wheel diagram (bottom)
are two absorption peaks, then the observed color will be a
combination of the two complementary colors. For instance, when two absorption peaks occur at
500 and 630 nm, the absorbed colors are green and orange; thus, the observed color is a
combination of blue and red, which is perceived as violet.
Spectrophotometryo to pileup sill as ano
This technique is of great importance throughout all branches of chemistry. There are two
essential types of information available from spectrophotometry:
. Qualitative information identifies a compound and/or gives information about structural
(features of a compound.
. Quantitative information reports on the concentration of a specific compound in solution.
Spectrophotometry is carried out in many regions of the electromagnetic spectrum from low
energy radio, microwave, and infrared to higher energy visible, ultraviolet and x-ray frequencies.
Each frequency range provides different and specific information which are further explored in
higher level chemistry and biochemistry courses. Although we will concentrate here on
spectrophotometry in the visible range of the spectrum, the same principles can be applied to
other regions of the spectrum.


Spectrophotometry #2: Analysis of a Mixture (S.S. Crimson Hawk)
Pre-laboratory Assignment. Based on your lab instructor's directions, read through the
experiment and a) answer the questions below; or b) complete the pre-lab assignment at Sapling
Learning online.
1. In Parts I and II, you will measure the absorbance of stock solutions of copper ion and nickel
ion. Copper (II) ions in aqueous solution are typically blue. Nickel (II) ions in aqueous solutions
are typically green.
a. What color of light is being absorbed in a Cut solution?
b. Around what wavelength do you expect a Cut solution to absorb?
c. What color of light is being absorbed in a Nit solution?
d. Around what wavelength do you expect a Nit solution to absorb?

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