4hMANEcellBatLED - Electrochemical Cells LEDs Revised...

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Electrochemical Cells & LEDs Revised 11/10/08 1 ELECTROCHEMICAL CELLS AND LEDs OBJECTIVES For you, the student, to write…. SAFETY Safety goggles and aprons must be worn in lab at all times. Solutions containing NH 3 and Na 2 S must be prepared in the hoods. Ammonia and sulfuric solutions are corrosive and can cause burns and respiratory problems; wash all affected areas thoroughly with cold water. Na 2 S can release toxic H 2 S gas when mixed with acids (tap water in the sink traps is acidic). The odor of H 2 S gas is similar to "rotten eggs". Use a dilute bleach solution to clean any spills containing sulfur. 6 M H 2 SO 4 is corrosive, use gloves while handling. Ventilate the room if the odor is strong and inform the TA so s/he can find the source. INTRODUCTION Electrochemical Cells In this part of the experiment, four “half cells” are created by immersing metal strips of zinc, copper, aluminum, and magnesium in aqueous solutions containing cations of the same element (Zn 2+ , Cu 2+ , Al 3+ , and Mg 2+ ). An electrochemical cell is created when two of these “half cells” are connected by a KCl salt bridge and a wire (the leads from the voltage probe). Six different electrochemical cells can be created from the four half cells above. A positive cell potential is measured when the black lead is connected to the anode and the red lead is connected to the cathode. Cell notation will be used to describe the electrochemical cells. A reduction table will be created by designating copper as the standard electrode. Cu 2+ (aq) + 2 e Æ Cu(s) E = 0.00 V
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Electrochemical Cells & LEDs Revised 11/10/08 2 Lead Acid Battery A typical car battery contains lead (Pb) and lead oxide (PbO 2 ) plates in a sulfuric acid solution. In this part of the experiment a simplified form of such a battery is created by immersing lead plates into a sulfuric acid solution. The electrodes are charged by connecting to a power supply (a 9V battery). During the initial charging, hydrogen and oxygen gas is generated by the electrolysis of water and the lead electrodes become partially coated with PbO 2 . The battery will be discharged by connecting the electrodes to a circuit containing a light emitting diode (LED). During the discharge process PbSO 4 (s) is created at both electrodes. When the battery is recharged, the discharge half-reactions are reversed and the electrolysis of water occurs (as it did during the initial charging process). Light Emitting Diodes In this part of the experiment, the battery created above will be used to light LED semiconductors. The light color (energy) emitted by and voltage drop through the LEDs will be used to determine the band gap size trend for the following LEDs: GaP 1.00 As 0.00 , GaP 0.85 As 0.15 , GaP 0.65 As 0.35 , GaP 0.40 As 0.60 . PROCEDURES
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4hMANEcellBatLED - Electrochemical Cells LEDs Revised...

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