CHM171L Physical Chemistry 2 Laboratory 4th Quarter AY 2015-2016
Photochemistry Ricky Jay C. Gomez1 1Students,
Mapúa Institute of Technology, School of Chemical Engineering and Chemistry
ABSTRACT The experiment was all about photochemistry or underlying capabilities of light in various chemical reaction. The objectives were to perform a 2D printing of an image using filter paper and a piece of printed image on an acetate. Using ferric chloride and oxalic acid mixed solutions, a chemical reaction was done in a dark and low light area. And by subjecting the immersed image in the solution, it was subjected to a area where there is a presence of strong light. As the whole exposed image turns into blue, it proves that a chemical reaction/photochemistry occurred. occurred. Keywords: Photochemistry, Photochemistry, light, ferric chloride, oxalic acid
INTRODUCTION Photochemistry studies the interaction between atoms, molecules and light or electromagnetic radiation. It is also the study of chemical reactions induced by direct or indirect light. At some situation, thermal reaction which takes place in the dark normally obtain the activation energy of the photon absorption of light by molecules, Possible outcome of this reaction yields to a high selectivity, which means that for a particular reaction the energy of quantum of light is appropriate. The amount of energy Ep of a photon is determined by the frequency of the oscillation of the electromagnetic field of which the equation is made: Ep=hv=hc/λ where h is the Planck’s constant, λ is the wavelength and c is the velocity of light. Photochemical reaction is a chemical reaction caused by light or ultraviolet radiation. Interaction of light with matter can be reflected, scattered, refracted, transmitted or absorbed. The first step in photochemistry is the absorption of light. Only the absorbed light can induce photochemical change. However, it doesn’t necessarily mean that it will result in any photochemical event. It is only the absorption of light that initiates chemical event. Thus, an important rule in photochemistry.
potassium ferricyanide as reagents. The mixture of reagents which will coat the paper is sensitive to light. The objective of the experiments is to visualize the effect of light on chemical reactions. The modern era of organic photochemistry began in 1866, when Russian chemist Carl Julius von Fritzche discovered that a concentrated anthracene solution exposed to UV UV radiation radiation would fall from the solution as a precipitate. This precipitation happens because the anthracene molecules join together in pairs, or dimers, which are no longer soluble. Photochemical reactions and the properties of excited states are also critical in many commercial processes and devices. Photography and xerography are both based upon photochemical processes, while the manufacture of semiconductor chips or the preparation of masks for printing newspapers relies on UV light to destroy molecules in selected regions of polymer masks. MATERIALS AND METHOD The experiment was done using a cardboard, glass, filter paper soaked with solution of Ferric Chloride (FeCl3), Oxalic Acid (H2C2O4), Potassium Ferrycyanide (K3(FeCN)6), and distilled water, and also by a acetate paper with the desired design (shown in Figure 1), and more importantly the presence of sunlight.
For the experiment, a blueprint process was performed with ferric chloride, oxalic acid and EXPERIMENT 07 | GROUP 05 | MAY 18, 2016
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Turnbull’s blue were immediately oxidized by the neighboring ions (ferrous). Once the acetate film was subjected to the filter paper submerged in the mixed solution and exposed to UV light, ferric oxalate gets reduced to ferrous oxalate with the release of carbon dioxide. After the blue color dominated the setup, the filter paper was washed carefully with water, and the part covered with a dark color or not exposed crucially in the sunlight was observed to have less blue color or no blue color at all. The finished design is shown in Figure 2. FIGURE 1: Design printed in acetate as a trace used in the experiment. Prepare a solution of ferric chloride and oxalic acid by dissolving 1g of both in a 50 mL distilled water placed in a beaker. Prepare another solution of potassium ferryicyanide by dissolving 1g of it in a 50mL water placed in a beaker. After preparing the two solutions, ready the acetate paper with design, filter paper, cardboard, glass, tray, and the two solutions in an area where light is reduced. Mix the two solutions p repared in the tray two create a uniform solution. After that, make sure to soak the whole filter paper in the uniform solution. Remove the excess solution, and immediately withdraw the paper. Still, while in the area where light is reduced, mount the soaked filter paper in the cardboard, and above the filter paper, mount the acetate paper with the desired design, and lastly mount the glass above the acetate paper. Lastly, place the design in an area where there is enough sunlight to turn the solution in the filter paper blue. Since the design in the acetate paper covers the solution in the filter paper from sunlight, the solution in that part won’t turn blue. After turning the solution to blue, go to an area where there is reduce light again, and wash the final design with plenty of water. Dry the final design. RESULTS AND DISCUSSIONS
Light is a form of radiation that possesses an energy that could be absorbed by atoms and molecules. To visualize the effect of light on chemical reactions proceeded by mixing ferric chloride, oxalic acid and potassium ferricyanide. This method is usually used in the process of blueprinting. In the said process, Ferric ions in a few organic-iron complexes are reduced by light. In this common reaction, the ferrous ions were formed and were made to react with K 3(FeCN)6 which normally results to a bluish compound normally known as the Turnbull’s blue. The ferrous ions in
EXPERIMENT 07 | GROUP 05 | MAY 18, 2016
FIGURE 2: Finished design of traced paper. CONCLUSION This experiment aims to visualize the effect of light on chemical reactions. This concept is explained by photochemistry, the study of chemical reactions, isomerization and physical behavior that may occur under the influence of visible and/or ultraviolet light is called photochemistry. Photochemical reactions are valuable in organic and inorganic chemistry because they proceed differently than thermal reactions. Many thermal reactions have their photochemical counterpart. In the case of photochemical reactions, light provides the activation energy. Simplistically, light is one mechanism for providing the activation energy required for many reactions. Everyday examples include photosynthesis, degradation of plastics or formation of vitamin D with sunlight. REFERENCES P. Atkins and J. de Paula, "Atkins' Physical Chemistry" (8th edition, Freeman 2006), chap.5 Levine, I.N. (2009). Physical Chemistry 6 th Edition. McGraw- Hill Companies, Inc. 2
