Question

Questions(Answer on an attached sheet of paper and turn in with the report) 1. Why do metals give off different colors in a flame test? 2. You spray paint the letters SPECTROSCOPY in yellow paint on snow. After a while the sun comes out and the snow under the yellow paint melts, leaving the letters in the word SPECTROSCOPY intact. Why did the snow under (rather than around) the yellow paint melt? 3. The graph below shows the absorption spectra for an acid indicator solution and a base indicator solution. What is the actual color of each solution? acidic4 0.5-basic L 0.6- ㄒㄧ-5-- 0.3 L-L o. 400 450 500 550 600 650 700 Wavelength (à) in nm 4. Identify the visible absorption spectrum of an aqueous solution of white sugar from the spectra (A or B or C) given below. Explain your choice 2.0 2.0 2.0 Abs Abs Abs 700 400 λ 700 400 λ 700 400

Answer 1

1) Different metals have different sets of valencies, which allows electrons to come out from different energy levels. This difference in energy levels produces a difference in energy of photons released by the emitting electrons, giving the difference in colors. When we heat the metal, the electrons get excited to different energy levels in different metals, and when they come back to their original position, towards stability, they tend to follow different paths. Some electrons drop directly to the low energy levels but some electrons jump to sub-energy levels to become stable. That is why they emit different sets of photons as the wavelength of the light depends on the difference in energy of different energy levels and hence different colors come.  

2) Yellow color has high absorbance for the spectrum produced by the sunlight, hence it also absorbs other colors from the sunlight. Thus, it generates more heat than the other colors. That is why the snow around or under the yellow color absorbs heat and melts.  

3) The actual color of each solution is the color where the graph of Absorbance vs Wavelength of the two solutions crosses each other. Thus, it can be seen that graphs are intersecting at a region in the blue color range. Thus, both solutions have a blue color.

4) As the amount of sugar is added in the solution, the absorption peaks become wider and wider, increasing the area between the peaks. So adding white sugar increases the absorbance of the solution, hence the visible light spectrum with the highest range will be the spectrum we need. In A and B, there is no range, absorption is constant, but in C, there is the difference in absorption as the wavelength increases, thus, C is the actual spectrum of aqueous white sugar solution.