Name: ________________________________ Electrochemical Cells: Virtual Activity Electrochemical cells involve the transfer of electrons from one species to another. In these chemical systems, the...

They are all about a lab


Name: ________________________________ Electrochemical Cells: Virtual Activity Electrochemical cells involve the transfer of electrons from one species to another. In these chemical systems, the species that loses electrons is said to be “oxidized” and the species that gain electrons is said to be “reduced”. A species cannot gain electrons unless another has lost electrons and vice versa. Oxidation and reduction go hand in hand. There are two major types of electrochemical cells: voltaic (also galled galvanic) and electrolytic. Voltaic cells produce electricity by harnessing the energy present in the flowing electrons. These reactions are spontaneous. Electrolytic cells use electrical energy to drive a redox reaction that normally would not occur because it is nonspontaneous. Part I: Standard Cell Potentials (Voltaic Cells) 1. Go to http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/electroChem/voltaicCell10.ht ml Make the following voltaic cells: #1: Cu2+/Cu | | Ag+/Ag #2: Zn/Zn2+ | | Ag+/Ag #3: Zn/Zn2+ | | Cu2+/Cu 2. For each of the above, place the metal in a solution of its own ions. Make sure the cells are set up so that the cell potential is a positive value, indicating that the voltaic cell is set up correctly and the redox reaction is spontaneous. (Hint: In this simulation, the anode is black and the cathode is red.) 3. For each of the three voltaic cells, record the direction of electron flow, determine which electrode is the anode and which is the cathode, and record the cell voltage in the table on the next page. 4. For each electrode, determine whether oxidation or reduction is taking place. Record this in the table. 5. For each electrode, determine whether the electrode is dissolving away (becoming an ion and going in to solution) OR gaining mass (ions in solution are becoming neutral atoms that are deposited on the electrode). Record this in the table. 6. You must click the “Off” switch to reset for the next voltaic cell. Click  here  to  select   metals  for  the  left-­‐ hand  side  of  the  cell   Click  here  to  select  a   solution  for  the  left-­‐ hand  side  of  the  cell   Click  here  to  select   metals  for  the  right-­‐ hand  side  of  the  cell   Click  here  to  select  a   solution  for  the  left-­‐ hand  side  of  the  cell   Part I Data Table Voltaic Cell # Electrodes Direction of electron flow Anode Cathode Eºcell (Volts) 1 Cu and Ag Oxidation or Reduction? Dissolving into solution or Gaining mass? 2 Zn and Ag Oxidation or Reduction? Dissolving into solution or Gaining mass? 3 Cu and Zn Oxidation or Reduction? Dissolving into solution or Gaining mass? Analysis Questions: Part I (show setups for any calculations) 1. What is another name for a voltaic cell? 2. For the first cell, Cu-Ag: (a) Write the oxidation AND reduction half-reactions. Label each as “oxidation” or “reduction”. (b) Write the balanced, net ionic equation for the reaction. 3. For the second cell, Zn-Ag: (a) Write the oxidation AND reduction half-reactions. Label each as “oxidation” or “reduction”. (b) Write the balanced, net ionic equation for the reaction. 4. For the third cell, Zn-Cu: (a) Write the oxidation AND reduction half-reactions. Label each as “oxidation” or “reduction”. (b) Write the balanced, net ionic equation for the reaction. Part II: Electroplating (Electrolytic Cells) 1. Go to http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/electroChem/electrolysis10.ht ml 2. Construct a copper electroplating cell by placing a copper anode and iron cathode in a solution of Cu2+ ions. (anode is red and cathode is black) 3. Record the initial mass of the iron cathode in the data table. 4. Run the simulation at a current of 2.00 amperes at 2.00 V for 5:00 minutes. Record the final mass of the iron cathode. Record in the data table and calculate the mass of copper deposited on the iron. Initial mass of Fe (g) Final mass of Fe (g) Mass of Cu deposited on Fe (g) Analysis Questions: Part III (show setups for any calculations) 1. Is electroplating a spontaneous reaction, or does it require energy? (Look at the voltage) 2. What attracts the Cu onto the Fe electrode? 3. State the direction of electron flow through the circuit. 4. Calculate the moles of copper formed. 5. Write the Cu half reaction that takes place on the Fe electrode as Cu is deposited. 6. How many moles of electrons are transferred when one mole of Cu is formed? 7. Calculate the moles of electrons that ran through this circuit in order for the Cu to form. (Multiply the moles of Cu by the moles of electrons traveling). AP Chemistry – Paper and Thin Layer Chromatography 1. A chromatogram of a single dye is shown here, along with three measurements. How should the Rf value be calculated for the dye? a. ? ?+? b. ? ?+? c. ? ?+?+? d. ? ?+?+? 2. Q is a sample of a pure substance whose Rf value is 0.9 with a given solvent. In the chromatogram shown here, which spot is Q? a. A b. B c. C d. D 3. Ethanol is a very volatile, highly polar solvent. It can be used to separate the dyes in a sample of ink. A student set up a chromatography experiment as shown here. Identify TWO errors that the student made in the set-up. Explain your answers. 4. A student was trying to identify pigments in a plant leaf. She performed a chromatography experiment on a leaf sample (shown below). In her experiment, the stationary phase was silica gel (high polarity) and the mobile phase was a mixture of hexanes and ethyl acetate (low polarity). She also determined the Rf values for 5 pigments using the same conditions. a. Show how to calculate the Rf value for the first spot in her chromatogram. b. Enter the Rf values for each of the four spots in her chromatogram in the table below. Then identify the pigments that are in the leaf sample, if possible. c. Which pigment is the most polar? Explain your choice. 5. Some students set up a chromatogram to analyze an ink sample and after 15 min the colours had separated as shown. Which diagram (A through D) might result if the experiment ran for another 30 min? Rf value Pigment ID Spot 1 Spot 2 Spot 3 Spot 4 Initial Setup After 15 min Which of these could result after 30 min longer?